Archive for the ‘Silverlight’ Category

Glossy Button

The MS Expression Blend tutorials contain a tutorial on creating a glossy button. Well, I like shiny things, so I got into it. The tutorial is very practically oriented, so in this blog post we’ll start with some remarks on lighting practices that might create the illusion of a shiny object on your screen.


With respect to lighting concepts, I will somewhat follow Frank D. Luna here. Factors at play in lighting are directional and wavelength attributes of the light(s) involved and reflective properties of the material the light.


For people, colored light is a compound of Red, Green and Blue light in varying intensities. The relative intensities of these components define the colors we know.

Ambient lighting is lighting of an object by indirect light, light that has been reflected multiple times, and thus has no specific source. In Ambient lighting models, neither the position of the observer nor the position of the light source plays a role. You might think of ambient light as showing the color of an object (dependent on the color of the light, of course).

Diffuse lighting of an object describes the scattering reflections of light coming from a specific source. The smoother the surface, the less diffuse its reflection, the shinier it looks. In Diffuse lighting models, the position of the light source, but not the position of the observer is defined. We could say that diffuse lighting creates a gloss on smooth surfaces.

Specular lighting of an object involves directed light that reflects (mostly) in a specific direction – ‘a cone of reflection’. In Specular lighting both the position of the light source and the observer is relevant – the observer might not see the specular reflection. We might say that specular lighting creates the shine on a smooth surface.

Light sources come in three flavors: parallel light sources, like the sun; point light sources, like a light bulb, and spotlights, like a flashlight.  In 3D models, parallel light has a direction but no source location; light from a point source has a source position and an
intensity that decreases quadratically with distance from the source. It lights objects in all directions. Spotlights have a source position, a specific direction and also attenuation. According to Lambert’s Cosine Law, reflected light intensity depends as the cosine function on the angle at which the light hits a surface, so perceived reflected light intensity depends on both the angle and the distance.


Material properties define which wavelengths will be absorbed and which will be reflected (and to what extent). This defines the color and smoothness properties. Rough material will reflect light diffusely in all directions. If subjected to a strong light source, it will glow brightly, but will have hardly any gloss, and no shine. Conversely a smooth object will have a clear gloss and almost act as a mirror for the specular light (for an observer in an adequate position).

Modeling lighting of a glossy button

In a DirectX or XNA application you can model lighting extensively, and the result will be quite realistic. This realism comes at the price of significant resources, which cannot be spent on ‘just’ a button, so the same effects will have to be simulated by other means. In this section we will first analyze the construction of the glossy button from the tutorial, and then add some more features – for fun and enlightenment.

The Glossy Button Tutorial starts out with an ellipse, the button, that has a gradient color (and a robust edge). The gradient thus covers both ambient and diffuse lighting. A second layer, the gloss, consists of an ellipse that has a white gradient color, running into transparency. It also has a mild blur effect. This ellipse covers about two thirds of the button. The final layer, the shine, is a third ellipse, a much smaller one that also has a gradient white color, moving into transparency. The result is pretty cool, isn’t it?

Had I already mentioned the drop shadow (bottom right)?

Well, although pretty cool, one may have some disturbing questions, like: ‘What exactly is the shape of this button?’, or, ‘Where does the light come from?’ The shape cannot be a sphere, for that the gloss extends too far to the bottom, or alternatively, the shine is too close to the top. Also, it is weird that the drop shadow is bottom right, while the shine is in the middle. I also do not think that this button is very shiny, it doesn’t look it has a top layer of glass, like really shiny things do (I will get into this really shiny stuff in another blog post). Finally, it is strange that the rim has the same color all around the button. So, the conclusion is that the ingredients may be there, but the recipe isn’t quite right.

I have tried to improve a bit on these shortcomings but in the eyes of the reader it might just as well have become worse, so read on ;- ).

The glossy button demo application

The demo application has a number of additional features, the simplest being a text on the button. Also, the size of the button is rather large here, but it can be set differently using Width and Height dependency properties without adversely affecting the visual properties or behavior of the control.

Color picker

The user can pick a color for the button using the color picker. The color you select is the bright color in the gradient. The application adds the dark end of the gradient itself. The rim is also set to the dark color derived from the selected color. The color picker control is part of the CodePlex Silverlight Contrib project.

Follow the mouse pointer

Although I’m not a fan of things on your desktop that follow your mouse pointer, I did provide the option here. It was either follow the mouse pointer or develop a kind of jog/shuttle control to move the three gradients over the surface of the button, and this is quicker. So what you see is that within a certain range around the button, the button gradient, the gloss and the shine all follow the mouse pointer. The button does seem to a spherical shape when you move around.

Proximity color effect

A more experimental addition is that when the mouse pointer comes close to the button, light intensity increases. This means also that for some lighter colors, the color changes if the mouse pointer is over the button. This would agree with the common experience that harsh white light dims or removes color.

Mouse Pressed visual state

When the left mouse button is pressed, a simple animation increases the size of the gloss and shine.

Concluding remarks

After some pondering about some nagging dissatisfaction with the results I realized that a really shiny button also reflects the objects nearby. Reflection is what really makes the difference. So, if you really want to have shiny buttons, you are in for true 3D models in you user experience. Although that seems a far cry, the general use of 3D modeled user interfaces seems to gain momentum now. Just note tendencies like the use of the Kinect, the integration of Silverlight and XNA, the use of 3D in CSS3 and Html5, and, of course 3D video – without glasses even.

On the other hand, shiny buttons that do not reflect are already part of the Apple UX. In that case you see that the buttons are more like colored glass. These subjects, glassy buttons, and 3D user interfaces, will be subjects of upcoming blog posts.

The Windows 8, HTML 5, and Silverlight Rumor Circus

In this blog post an overview of the recent wave of fear and anger across the internet concerning the future of .Net in Windows 8 (could be released Autumn 2012), and why it is all a storm in a teacup.

Where and when it started

It all started with the demo of Windows 8 on the AllThingsD Conference (June 1)by Julie Larson-Green and Steven Sinofsky who mentioned that the applications presented were, and further applications could written in Html5 and JavaScript (version 1.8.5, together with CSS 3.0 called the HTML technology stack). Throughout the demo there was no mention of Silverlight or WPF. “This, What Has Not Been Said” tapped into already slumbering fears that HTML5 will compete out Silverlight. Heated reactions followed in discussion groups. See e.g. this one, where the thread was closed by the moderator. Some people, clearly driven by a distinct dislike of the Microsoft company stirred up the fire, as did a journalist of a respected medium.

What it is about

The fear mentioned above is the fear of many developers that costly investments of time and effort will become useless with the release of Windows 8. Of course, if there is only the risk that .Net software would be legacy at the release of Windows 8, investments in .Net and Silverlight software would stop immediately. Not only is there fear, but also dislike. Some developers express the opinion that the HTML5 tech(nology) stack is inferior to Silverlight, and also tedious to work with.

Does it seem justified?

I myself doubt this fear and uproar is justified. The HTML5 tech stack consists of ‘standards’ that are not finished, and have implementations that diverge across browsers, thus forcing web application developers to provide multiple implementations of the same functionality – who would like to pay for that? I know people that sell over the web and implement their web shop in HTML version Long.Ago to guarantee broad accessibility; this is what the Browser Wars have accomplished – people do not like to invest in new versions of the Html tech stack. Microsoft will not make itself dependent on these ‘standards’ it does not control.

Furthermore, Silverlight can do things that the HTML5 tech stack in itself cannot, or never will be allowed to do, if only for security reasons, see e.g. Microsoft’s refusal to support WebGL). Would Microsoft suddenly turn around, embrace this technology and replace its own? Unlikely.

However, Microsoft also didn’t move to take away the fears; they have the Build Conference in September 2011 at which they will tell more. Nevertheless, one might expect some indirect damage control, and it came quickly.

Damage control – differing opinions

First there was the blog post by David Burela referring to analysis of a leaked early Windows 8 build. The conclusion seems to be that software that will be built on top of Windows 8, will be built with .Net and Xaml. A particular group of applications, called ‘immersive’ applications (running within the Windows Shell) can be build using Html5 and JavaScript, much like some types of applications for Vista.

Mary Jo Foley of ZDNet goes further and publishes parts of correspondence with developers who have actually analyzed the early Windows 8 build. The picture that arises from that article is that an improved version of the .Net runtime (referred to as the Windows Runtime) will be central in Windows 8, and is programmable by Xaml in concert with a wide variety of programming languages, i.e. it is like Silverlight / WPF. Within Windows 8, XNA can be used for 3D graphics. Windows 8 apps built using ‘.Net’ should be easy to port to other devices – phones, tablets, etc. say by recompiling and compensating for the form factor. The Html5 apps might depend on the Windows Runtime as well (MD: this would explain the little understood remarks from Microsoft about native support of Html5). WPF and Silverlight may cease to exist as such in Windows 8, but the constituent technologies will be there.

In conclusion, it seems as if Microsoft is creating the facilities to build apps in Windows 8 using the HYML5 tech stack, as an addition to the .Net framework, rather than as a replacement. The motivation to do so, by the way, is to attract more, new developers to the platform. It does not seem to be the case that ‘immersive’ application can be build only in Html5. It seems that ‘Immersive’ is just a namespace, defining an API that is required to build applications which run within the Windows 8 shell.


OK, so software can be built using a variety of .Net languages, among which C++, and the runtime seems to be closer to the metal, thus providing higher performance, because immediate OS layers have been removed.

But there is more. C++ seems to be in what is called a ‘renaissance’. More developers use it in order to gain higher performance, a new specification (C++0x) is on its way, and C++ is recently declared by Google to be the best high performance programming language.

For the next version of Visual Studio (also to be released in 2012) Microsoft announced the AMP Accelerated Massive Parallelism library at the AMD Fusion Developer Summit. AMP promises to provide full C++ access to a heterogeneous set of processors and their memory models. That is to say: you write one program that executes both on a computer with GPU, as well as one without it. Note that GPU’s are not considered to be restricted to rendering graphics. These people consider a GPU a broadly applicable parallel processor (and indeed, there exist Graphics cards without a monitor connector). The demos shown by Sutter and Moth reflect awesome performance; over 1000GFlops.

AMP aims at extreme scalability of single executables, from very simple hardware architectures of a single core processor with dedicated RAM, up to extreme scaling out in Cloud configurations. Sutter showed the aimed for heterogeneity in running an executable on a pc with a multi core CPU with onboard GPU, and also a double separate GPU installed.

My guess is that all this nice stuff also will reflect on the ways software can be build with the evolution of .Net and Xaml on Windows 8.

Pixel Shader Based Expansion

Best animation performance in Silverlight 4 is obtained from the combination of procedural animation and a pixel shader, as reported in a previous blog. A pixel shader is not really meant to be used for spatial manipulation, but in Silverlight 4 vertex and geometry shaders are not available. Also, pixel shaders are limited to Model 2 shaders in Silverlight 4, and only limited data exchange is possible. The question is then, “how far can we push pixel shaders model 2”. Another previous blog post discussed a preliminary version of dispersion. This post is about Expansion. The effect is much like Dispersion, but the implementation is quite different – better if I may say so. Expansion means that a surface, in this case a playing video is divided up in blocks. These blocks then move toward, and seemingly beyond the edges of the surface.

The Pixel Shader

The pixel shader was created using Shazzam. The first step is to reduce the image within its drawing surface, thus creating room for expansion. Expansion is in fact just translation of all the blocks in distinct direction that depend on the location of the block relative to the center of the reduced image.

In the pixel shader below, parameter S is for scaling, reducing, the pixel surface. Parameter N defines the number of blocks along an axis. So if N = 20, expansion concerns 400 blocks. In the demo App I’ve set the maximum for N to 32, which results in 1024 blocks tops. Parameter D defines the distance over which the reduced image is expanded. If the maximum value for D is the number of blocks, all the blocks (if N is even), or all but the center block (N is odd) just ‘move off’ the surface.

The code has been commented extensively, so should be self explanatory. The big picture is that the reduced, centered and then translated location of the blocks is calculated. Then we test whether a texel is in a bloc, not in an inter block gap. If the test is positive, we sample the unreduced, uncentered and untranslated image for a value to assign to the texel.

sampler2D input : register(s0);

// new HLSL shader

/// <summary>Reduces (S: Scales) the image</summary>
/// <minValue>0.01</minValue>
/// <maxValue>1.0</maxValue>
/// <defaultValue>0.3</defaultValue>
float S : register(C0);

/// <summary>Number of blocks along the X or Y axis</summary>
/// <minValue>1</minValue>
/// <maxValue>10</maxValue>
/// <defaultValue>5</defaultValue>
float N : register(C2);

/// <summary>Displaces (d) the coordinate of the reduced image along the X or Y axis</summary>
/// <minValue>0.0</minValue>
/// <maxValue>10.0</maxValue> // Max should be N
/// <defaultValue>0.2</defaultValue>
float D : register(C1);

float4 main(float2 uv : TEXCOORD) : COLOR
	/* Helpers */
	float4 Background = {0.937f, 0.937f, 0.937f, 1.0f};
	// Length of the side of a block
	float L = S / N;
	// Total displacement within a Period, an inter block gap
	float d = D / N;
	// Period
	float P = L + d;
	// Offset. d is subtracted because a Period also holds a d
	float o = (1.0f - S - D - d) / 2.0f;
	// Minimum coord value
	float Min = d + o;
	// Maximum coord value
	float Max = S + D + o;

	// First filter out the texels that will not sample anyway
	if (uv.x >= Min && uv.x <= Max && uv.y >= Min && uv.y <= Max)
		// i is the index of the block a texel belongs to
		float2 i = floor( float2( (Max - uv.x ) / P , (Max - uv.y ) / P  ));

		// iM is a kind of macro, reduces calculations.
		float2 iM = Max - i * P;
		// if a texel is in a centered block,
		// as opposed to a centered gap
		if (uv.x >= (iM.x - L) && uv.x <= iM.x &&
		    uv.y >= (iM.y - L) && uv.y <= iM.y)
			// sample the source, but first undo the translation
			return tex2D(input, (uv - o - d * (N -i)) / S );
			return Background;
		return Background;

Client Application

The above shader is used in an App that runs a video fragment, and can be explored at my App Shop. The application has controls for image size, number of blocks, and distance. The video used in the application is a fragment of “Big Buck Bunny”, an open source animated video, made using only open source software tools.


Each of the above controls can be animated independently. Animation is implemented using Storyboards for the slider control values. Hence you‘ll see them slide during animation. The App is configured to take advantage of GPU acceleration, where possible. It really needs that for smooth animation. Also the maximum frame rate has been raised to 1000.

Performance Statistics

The animations run at about 225 FPS on my pc. This requires significant effort as from the CPU –about 50% of the processor time. The required memory approaches 2.3Mb.

Pixel Shader Based Panning

Best animation performance in Silverlight 4 is obtained from the combination of procedural animation and a pixel shader, as reported in a previous blog. I know, a pixel shader is not really meant to be used for spatial manipulation. However, in Silverlight 4 vertex and geometry shaders are not available. Also, pixel shaders are limited to Model 2 shaders, and only limited data exchange is possible. The question is then, “how far can we push pixel shaders model 2”. Another previous blog post discussed a preliminary version of dispersion. This post is about Panning. Panning means here that the size and coordinates of a sub frame of, in this case a video, are changed.

The Pixel Shader

The pixel shader was created using Shazzam. The first step is to reduce the image within its drawing surface, thus creating a frame that works as a window through which parts of the video are visible. Panning is in fact just changing the coordinates of this window while correcting for the change in coordinates when sampling the source texture.

In the pixel shader below, the BlockSize in [0, 1], BlockX, and BlockY, both in [0, 1] define the panning window. The Bound function centers the panning window for coordinate values of 0.5. In the Main function, the ‘space’ variable denotes the available space to move the panning window around in. BlockH and BlockV denote the topmost horizontal and leftmost vertical edges of the panning window. We use these to filter input coordinates that sample the color texture. Other texels get assigned the background color of the demo application.

sampler2D input : register(s0);

// new HLSL shader

/// <summary>Size of BLock</summary>
/// <minValue>0.0</minValue>
/// <maxValue>1.0</maxValue>
/// <defaultValue>1.0</defaultValue>
float BlockSize : register(C2);

/// <summary>Horizontal Block selection</summary>
/// <minValue>0.0</minValue>
/// <maxValue>1.0</maxValue>
/// <defaultValue>0.5</defaultValue>
float BlockX : register (C3);

/// <summary>Vertical Block selection</summary>
/// <minValue>0.0</minValue>
/// <maxValue>1.0</maxValue>
/// <defaultValue>0.5</defaultValue>
float BlockY : register (C4);

float2 Bounds(float coord, float space)
	// Scale coordinate to available space
	float blockStart = coord * space;
	return float2(blockStart, blockStart + BlockSize); // 2nd argument is block end

float4 main(float2 uv : TEXCOORD) : COLOR
	/* Helpers */
	// Background Color
	float4 Background = {0.937f, 0.937f, 0.937f, 1.0f};
	// Available space to move around
	float space = 1.0f - BlockSize;

	/* Define Block */
	float2 BlockH = Bounds(BlockX, space);
	float2 BlockV = Bounds(BlockY, space);

	// If uv in BLock, sample
	if (uv.x >= BlockH.x && uv.x <= BlockH.y &&
	    uv.y >= BlockV.x && uv.y <= BlockV.y)
		return tex2D(input, uv);
		return Background;

Client Application

The above shader is used in an App that runs a video fragment, and can be explored at my App Shop. The application has controls for panning window size, X-coordinate and Y-coordinate of the panning window on the video surface. The video used in the application is a fragment of “Big Buck Bunny”, an open source animated video, made using only open source software tools.


Each of the above controls can be animated independently. Animation is implemented using Storyboards for the slider control values. Hence you‘ll see them slide during animation. The App is configured to take advantage of GPU acceleration, where possible. It really needs that for smooth animation. Also the maximum frame rate has been raised to 1000.

Performance Statistics

The animations run at about 270 FPS on my pc. This requires both significant effort from both the GPU as from the CPU – both about 35% of the processor time. The required memory approaches 2.2Mb.

Pixel Shader Based Translation

Best animation performance in Silverlight 4 is obtained from the combination of procedural animation and a pixel shader, as reported in a previous blog. I know, a pixel shader is not really meant to be used for spatial manipulation. However, in Silverlight 4 vertex and geometry shaders are not available. Also, pixel shaders are limited to Model 2 shaders, and only limited data exchange is possible. The question is then, “how far can we push pixel shaders model 2” Another previous blog post discussed a preliminary version of dispersion, which is fairly complicated. This post is about translation. Translation means here that the coordinates in the 2-dimensional plane of a reduced image, in this case a video, are changed.

The Pixel Shader

The pixel shader was created using Shazzam. The first step is to reduce the image within its drawing surface, thus creating the room required for translation. Translation is in fact just changing the coordinates of the reduced images while correcting for the change in coordinates when sampling the source texture.

The pixel shader below, the if statement does the filtering. Left and Right are parameterized offset and cutoff values. The offset ‘Left’ is also used to correct for the displacement in sampling. Sampling is done by the ‘tex2d’ function.

sampler2D input : register(s0);

// new HLSL shader

/// <summary>Reduces the image</summary>
/// <minValue>0.01</minValue>
/// <maxValue>1.0</maxValue>
/// <defaultValue>0.33</defaultValue>
float Scale : register(C0);

/// <summary>Changes the coordinate of the reduced image along the X axis</summary>
/// <minValue>0.0</minValue>
/// <maxValue>1.0</maxValue>
/// <defaultValue>0.5</defaultValue>
float OriginX : register(C1);

/// <summary>Changes the coordinate of the reduced image along the Y axis</summary>
/// <minValue>0.0</minValue>
/// <maxValue>1.0</maxValue>
/// <defaultValue>0.5</defaultValue>
float OriginY : register(C2);

float4 main(float2 uv : TEXCOORD) : COLOR
	float4 Background = {0.937f, 0.937f, 0.937f, 1.0f};
	float2 Origin = {OriginX, OriginY};
	// Reduce nr. of computations
	float halfScale = 0.5 * Scale;
	float2 Left = Origin - halfScale;
	float2 Right = Origin + halfScale;

	// Filter out texels that do not sample (the correct location)
	if (uv.x >= Left.x && uv.x <= Right.x && uv.y >= Left.y && uv.y <= Right.y)
		return tex2D(input, (uv - Left) / Scale);
		return Background;

Client Application

The above shader is used in an App that runs a video fragmant, and can be explored
at my App Shop. The application has controls for video surface reduction, translation along the X-axis, and translation along the Y-axis. The video used in the application is a fragment of “Big Buck Bunny”, an open source animated video, made using only open source software tools.


Each of the above controls can be animated independently. Animation is implemented suing Storyboards for the slider control values. Hence you‘ll see them slide during animation. I didn’t use procedural animation, since, as discussed in the aforementioned previous blog post, is hindered by the implementation of the MediaElement.

The App is configured to take advantage of GPU acceleration, where possible. It really needs that for smooth animation. Also the maximum frame rate has been raised to 1000.

Performance Statistics

The animations run at about 250 FPS on my pc. This requires both significant effort from both the GPU as from the CPU. The required memory reaches a little over 3.5Mb.

Spatial Transformation by Pixel Shader

As reported in a previous blog, best animation performance in Silverlight 4 is obtained from the combination of procedural animation and a pixel shader. A pixel shader is meant to be used for the manipulation of colors and transparency, resulting also in lightning and structural effects that can be expressed pixel wise.

A pixel shader is not really meant to be used for spatial manipulation – spatial information is hard to come by, but see e.g. this discussion on the ShaderEffect.DdxUvDdyUvRegisterIndex property. Vertex shaders and geometry shaders exist to filter, scale, translate, rotate and filter vertices and topological primitives respectively. Another limitation of the use of shaders in Silverlight 4 is that only model 2 pixel shaders can be used, so that only 64 arithmetic slots are available. Finally, you can apply only one pixel shader to a UIElement.

In order to explore the limitations on spatial manipulation and the number of arithmetic slots, I decided to build a Silverlight 4 application that does some spatial manipulation of a playing video by means of procedural animation and a pixel shader. Well, this is also my first encounter with pixel shaders, so I gathered that a real challenge would show me many sides of pixel shaders (and indeed, no disappointments here).

The manipulation consists of two steps. First the video surface is reduced in size in order to create some space for the second step. In the second step, the video is divided up in a (large) number of rectangles which drift apart – disperse, while reducing in size. The second step is animated.

To be frank, I’m not very excited about the results so far. It definitely needs improvement, but I need some time and a well defined starting point for further elaboration.

The completed application

You can explore the completed application, called ‘Dispersion Demo’ in my App Shop. The application is controlled by 4 parameters:

  1. Initial Reduction. This parameter reduces the video surface. The higher the value, the greater the reduction.
  2. Dispersion. The Dispersion parameter controls the amount of dispersion of the blocks. If you set both Initial Reduction and Dispersion to 1, you can see the untouched video.
  3. Resolution. The Resolution is a measure for the number of blocks along both the X-axis, and the Y-axis.
  4. Duration. Controls the duration of the dispersion animation.

The application also has three buttons to Start, Stop, and Pause the animation of the Dispersion. The idea is that you first select an initial Reduction and a Resolution and then click Start to animate the Dispersion.

The video used in the application is a fragment of “Big Buck Bunny”, an open source animated video, made using only open source software tools (and an astonishing amount of talent).

Performance statistics

The use of some procedural animation and the pixel shader results on my pc in a frame rate of about 198 FPS, and a footprint of about 2Mb video memory. This is good (though ~400FPS would be exciting), and leaves plenty of time for other manipulations of the video image.

The pixel shader

The pixel shader was created using Shazzam, an absolutely fabulous tool, and perfect for the job. The pixel shader shown below centers the image or video snapshot and reduces it. Then it enlarges it again according to the Dispersion factor. The farther away from the center, the larger the gaps are between the blocks displaying video, and the smaller the blocks themselves are.

sampler2D input : register(s0);

// new HLSL shader

/// <summary>Reduces image to starting point.</summary>
/// <minValue>1.0</minValue>
/// <maxValue>20.0</maxValue>
/// <defaultValue>10.0</defaultValue>
float Scale : register(C0);

/// <summary>Expands / enlarges the image.</summary>
/// <minValue>1</minValue>
/// <maxValue>20</maxValue>
/// <defaultValue>6</defaultValue>
float Dispersion : register(C1); //Dispersion should never get bigger than Scale!!!

/// <summary>Measure for number of blocks</summary>
/// <minValue>100</minValue>
/// <maxValue>800</maxValue>
/// <defaultValue>200</defaultValue>
float Resolution : register(C2);

float4 main(float2 uv : TEXCOORD) : COLOR
       float ratio = Dispersion / Scale;
       float offset = (1 - ratio) / 2;
       float cutoff = 1 - offset;
       float center = 0.5;
       float4 background = {0.937f, 0.937f, 0.937f, 1.0f}; // Same as demo program's Grid

       float2 dispersed = (uv - offset)  / ratio;
       float2 limit = 4 * (abs(uv - center) * (Dispersion - 1) / (Scale - 1)) - 1;

       if(uv.x >= offset && uv.x <= cutoff && uv.y >= offset && uv.y <= cutoff)
             if (sin(dispersed.x * Resolution) > limit.x &&
                 sin(dispersed.y * Resolution) > limit.y)
                    return tex2D(input, dispersed);
             else return background;
       else return background;

In the code above, the outer “if” does the scaling and centering. The sine function and Limit variable take care of the gaps and block size. See the graph below, the Limit rises to cut off increasingly many values of the sine, thus creating smaller blocks and larger gaps.

Evaluation of limitations

Although this is a solution for the challenge set, it is not the solution. This solution uses scaling for dispersion, but what you really would like to have is a translation per block of pixels that disperse. Needing this reveals another limitation: in Silverlight 4 you cannot provide your pixel shader with an array of structs that define your blocks layout, hence it is very hard to identify the block a certain pixel belongs to, and thus what its translation vector is.

At this point I had the idea to code the block layout into a texture which is made available to the pixel shader (you can have up to three extra textures (PNG images) in your pixel shader. To create such a lookup map you have to create a writeable bitmap with the values you want, then convert this to a PNG image as Andy Beaulieu shows, using Joe Stegman’s PNG encoder. The hard part will be the encoding (and decoding in the shader). You have at your disposal 4 unsigned bytes, and you will have to encode 2D translation vectors that also consist of negative numbers. The encoding / decoding will involve a signed – unsigned conversion, and the encoding shorts (16 bit integers) as 2 bytes. This will, of course, be a feasible but tedious chore.

A better move would be to invest some effort in getting acquainted with Silverlight 5 Beta’s integration with XNA, by which also vertex shaders come available.

As far as the limit of 64 arithmetic slots concern, it seems that one absolutely must hit it. But then, it always seems possible to rethink and simplify your code, thus reducing its size. This limitation turned out not very prohibitive.

Procedural animation

The above pixel shader is integrated in the Silverlight application using the C# code generated by Shazzam. Then when implementing procedural animation, another limitation came up concerning manipulating videos.

The initial plan was to display the video using a collection of WriteableBitmaps that could be manipulated using the high performance extensions from the WriteableBitmapEx library. However, it turns out that to take a snapshot from a MediaElement, you have to create a new WriteableBitmap per snapshot. This is expensive since we now have to create at least about 30 WriteableBitmaps per second. Indeed, running the Dispersion application (at 198 FPS) sets the CPU load to about 50% at my pc. This is not really what we are looking for.

A way out is to implement the abstract MediaStreamSource class, both for the vision part as well as for the sound part of the video to be exposed. By the looks of it, this seems to be quite a challenge. However, Pete Brown has provided examples for both video and sound. And there is also the CodePlex project that provides the ManagedMediaHelpers. So, we add this challenge to the list.

Another experiment might be to see if the XNA sound and video facilities can be accessed when exploiting the Silverlight – XNA integration in Silverlight 5.


The challenge set turned out to be very instructive. I’ve learned a lot about writing pixel shaders, though there will be much more to learn. No doubt about that.

It is absolutely true that spatial manipulation is hard in pixel shaders :-), the main cause being the extraordinary effort required to provide the shader with sufficient data, or sufficiently elaborate data. The current shader needs improvement, the next challenge in writing shaders will address Silverlight 5 (beta) and XNA.

I noticed that you can achieve a lot in pixel shaders using trigonometry, and (no doubt) the math of signals.

Finally, in order to really do procedural animation on surfaces playing parts of a video, you seem to need to either implement MediaStreamSource or get use the XNA media facilities.

Silverlight massive animation performance

As it turns out, Storyboard animations in Silverlight have limited performance capability. Presumably this system has been designed for ease of use and developer / designer productivity. If you want to create massive amounts of animations, like for instance in particle systems, you soon hit the performance limits of the rendering, graphics, animation subsystem.

Hey, that’s interesting!

Of course, now we want to know what the performance limits are, and how we can get around them. When I first hit the aforementioned performance limits, I had no clue as to how to improve performance. In this article you will find some articles I found on the World Wide Web concerning the subject. Great stuff. Some solutions found are about 20 times faster than others, and current developments of Silverlight 5 seems to promise to take it a step further.

Growing trees

The first article encountered was How I let the trees grow by Peter Kuhn. He describes how he ran into performance problems creating a tree that grows by splitting branches into smaller branches, terminating in leaves. At some point he finds his software trying to render over 20k paths, which is ‘massive’ enough to create performance problems. The solution is found in the use of the WriteableBitmapEx CodePlex project. The WriteableBitmapEx contains (among others) a fast Blit operation for copy operations (claimed to be 20-30 times faster than the standard Silverlight operation – I believe it). You can draw on Bitmaps that are not shown yet, thus prepare images for the screen, and then quickly shove them into vision when ready. The (in browser – IE9) solution presented performs well.

What we do not get from this article are clear figures about standard Silverlight performance and improved performance. So let’s discuss another article.

Procedural animations

The WriteableBitmapEx CodePlex project contains a reference to Advanced Animation: Animating 15,000 Visuals in Silverlight by Eric Klimczak. He tells us that if we want to animate ~50 objects concurrently, we need additional performance measures over Storyboards and Timelines. The main performance measures he employs extend the ones mentioned above with: “procedural animations”.

In Procedural Animation within the context of Silverlight you code an Update() and Draw() Loop that is driven by the Windows.Media.CompositionTarget.Rendering event. Essentially, you now code the new position, color, or any other attribute, in the Update() method, and Blit it to the render target in the Draw() method – thus putting it on screen.

This works very well! Eric Klimczak has provided source code with his article, among which a program that animates moving particles that respond quickly to mouse actions (in browser).

For 3000 particles the program renders at ~200 frames per second (FPS), tops, and 15.000(!) particles are rendered at a still pleasant 36 – 46 FPS. I’ve used the Silverlight FPS counter for all Silverlight programs in this article in order to get comparable measurements. See the fps counter in the status bar of the IE screenshot below.

Curiously, there is no maxFrameRate setting in his code. About this maxFrameRate setting the Silverlight documentation writes:A value of approximately 60 frames-per-second should be reliable on all platforms. The 1000 and 30000 frames-per-second range is where the maximum frame rate could differ between platforms”. So, the obvious step is to set the maxFrameRate to 1.000 – both in code as well as in the html host, which showed a factor 3 performance increase compared to the original article software, for the 3K particle case (screenshot above). The Silverlight Documentation also states that the enableGPUAcceleration setting doesn’t work for the WriteableBitmap, so I skipped that one.

It seems to me that this approach solves most problems. However, procedural animation – a gaming software approach – opens the door to other, even more apt approaches.

Note that this approach does not employ the GPU. All rendering is done using the CPU.

Pixel shaders

An approach that takes performance a step further is Silverlight 3 WriteableBitmap Performance Follow-Up by René Schulte. In this article a number of approaches are compared. All approaches yield comparable results, except the pixel shader approach, which yields a factor ~20 better performance compared to the WriteableBitmap (WOW!).

How does it work? UIElement descendants have an Effect property. You can create custom Effects using a pixel shader written in HLSL (a .fx file) which you compile using e.g. fxc.exe – the DirectX HLSL compiler, or Shazzam. The compiled shader effect is loaded as a resource by a descendant of the ShaderEffect class. The article by René Schulte uses a custom derived class thereby showing how to transfer data into the shader during program execution. The loaded shader should be attached to the UIElement’s Effect Property. The shader will be executed for each pixel to be rendered. This gives you great control over the UIElement. You can modify many attributes of each pixel, for instance color and opacity. Do not forget that dropshadows are implemented as shaders, so you can also duplicate the UIElement visual.

According to René Schulte, the program / pixel shader is not executed on the GPU. That may have been true for Silverlight 3, but in Silverlight 4 it is absolutely possible to put the GPU to work. So, with a bit of tweaking the code here and there we find a maximum performance of >450 FPS.

I’ve registered the GPU invocation for specific tasks using the Catalyst utility of my graphics card, see the fields ‘GPU Clock’ and ‘Memory Clock’ at the bottom of the screen shot below. Regular values are 157 and 300 respectively.

Silverlight 5 Beta and XNA

Recently (April 13th 2011), Silverlight 5 Beta was released. It includes the DrawingSurface control which is a gateway into XNA functionality. A little experimenting reveals that like XNA the default drawing frequency is at 60 FPS, and you can’t seem to get it up by recurring calls to the OnDraw() event handler.

In Silverlight the frequency is raised as described above. In XNA the default of 60 FPS can be lifted by setting both the Game’s object ‘IsFixedTimeStep’ property and the GraphicsDeviceManager’s ‘SynchronizeWithVerticalRetrace’ property to false.

From the MIX demo video it is clear that performance is very good, however, at 60 FPS within Silverlight.  The performce step is ‘made’ by the shaders and realized on the GPU. It is currently not clear to me how to measure that performance, so this exercise ends here for now.

Non Silverlight performance

What performance can we expect? Is Silverlight slow, despite the extra tricks? What is the promise hidden in Silverlight 5? We now know that for demanding graphics we can turn to the integration of Silverlight with XNA. XNA, in turn is built upon DirectX.

Below you’ll find a screenshot of a DirectX11 particle demo. For 16K particles (reminiscent of the 15K in the above particle demo) we see a performance of ~620 FPS (not measured with the same frame counter as with the other programs, however), immediately requiring maximum performance from the GPU. For 8K particles performance rises to ~1175 FPS.

One conclusion I would like to draw here is that this performance correlates to the performance of the pixel shader used as a custom Effect. So, we may conclude that the real performance enhancement lies with the use of shaders.

Will this performance hold up in XNA? Yes, a particle simulation in XNA (from the XNA community, with small adaptation) brings us a ~1000 FPS performance, see screenshot.


The above is an exploration of techniques and approaches to realize massive animation performance in Silverlight. It is not a methodological, comparative study. A more rigorous investigation into performance (of what exactly?) might be subject for a later article that builds on the findings presented here.

Here we have learnt that in order to have massive animation in Silverlight we use the WriteableBitmap, the Blit operation from the WriteableBitmapEx Codeplex project, Procedural Animation programming, and pixel shaders (do not forget the enableGPUAcceleration setting, when applicable). We have seen that the exposure of XNA, built on DirectX, in Silverlight will most likely bring us further performance improvements.

Today we can have a very powerful massive animation performance of around 400-500 FPS, and the future is bright.

Rebuilding the App Shop

During the past couple of weeks I’ve rebuilt my App Shop, the portal that backs up posts in this blog with demo applications, where I keep solutions to problems I’ve built for the community, and other items of my portfolio. The App Shop is now a pure Silverlight application; you can access it only if you have Silverlight 4+ installed on your computer. This blog and the Silverlight community pages are the broadly accessible entrance to my work and portfolio.

So, anything worth mentioning about this rebuilt portal? Well, I like to think so. If one builds a portal like this, there are a number of requirements that need careful, integrated implementation. These requirements, concerning Compositionality, Navigation, MVVM implementation, and Blendability, will be discussed below.



Reasons why you want your Silverlight application to be composed of small components that are downloaded selectively only if they are required (and cached after that) are abundant. The web server that hosts the App Shop, for instance, is located at my home. Measurements show that the upload speed from my home to an Internet Backbone is 0.8Mbits/s. So if you request the portal to show an App, that App just has to be small, or streamed, in order to provide an acceptable download experience.

Despite the slow upload connection to the World Wide Web, visitors of the portal should have a first view of the portal quickly. So, the portal has to start from a small initial component.

The App Shop also has to be easily extensible, where easy also means ‘without recompilation’. Since this is an App Shop you might expect that Apps will be added to it at a regular basis. Since this whole portal is about the Apps, and only about the portal itself in as far as it is a (going to be) showcase of a portal that I could build, it should not take much effort to add Apps to it.

A final compositionality requirement is that shared assemblies, such as the Silverlight System assemblies should be downloaded only once, then reused by further downloaded components.


Navigation requires a master page and components one can load into the uniform environment the Master provides. In an extensible portal, you also want the navigation functionality to be extensible without compilation.


Blendability means Editable in MS Expression Blend. This is a requirement I’ve learned from Laurent Bugnion. It was a major design theme in his MVVM-Light toolkit, and he is right. Blend is a fine design environment for Silverlight applications. It definitely allows you to scale up your design results. That is: while working in Blend, you generate an enormous and amorphous amount of XAML, so much one might wonder if it is feasible to do this all by hand, or in Visual Studio. Examination of the XAML code will show you in such cases that it is not obviously or overly bloated – some even call it efficient code.

So, being able to use Blend allows you to create at least one level higher up designs than if precluded its use by the design of your software system.

Implements MVVM

One way to preclude the use of Blend is to implement MVVM (Model View ViewModel) in a clumsy way. Connecting a ViewModel to a View as a resource that acts as the DataContext is a right way.

To be honest, I’ve had my doubts about this requirement. Implementing MVVM adds much extra complexity, just to be able to test the code automatically. Nevertheless, it’s good to have this technique in your developer’s toolbox. So, that’s why we have MVVM in this not very complex application.



Or, the Managed Extensibility Framework. This is really cool stuff. MEF is a very versatile compositionality framework. It works by attributing types as exports, that are subsequently discovered by MEF. Instantiations of exported types are inserted at variable declarations that are attributed as imports. For a real good introduction into MEF for Silverlight see the Hello MEF blog post series by Glenn Block.

Notably, a component that imports a class doesn’t need to know anything about the imported class. The import is guaranteed to implement a contract (interface) as specified by the importing class, or MEF will not insert it as an import. Components that are attributed as Exports can depend on Imports themselves. Developing software using MEF is a bit like Primordial Soup programming. You specify the interfaces or dependencies between the components and objects without wondering for a single moment how the required objects get at the desired locations.

Given the way MEF works, it can be applied in IoC / DI (Inversion of Control / Dependency Injection) scenario’s, for pure compositionality of course, for navigation in Silverlight, and for the implementation of MVVM. This last application of MEF relieves one of the task of manually maintaining the relation between a View and a ViewModel, while maintaining Blendability.


As indicated above, MVVM is a very important software development pattern. Its main advantage is that it allows for automated unit testing, hence test driven development. A developer should have mastered this technique. Implementing MVVM is usually supported by a toolkit. The MVVM-Light toolkit by Laurent Bugnion is at the time of writing the dominant MVVM toolkit.

The MVVM-Light Toolkit is popular and respectable, but after having done some trials with it, I didn’t like it after all. The “why” lies mainly with the global ViewModel locator, an implementation of the Service Locator pattern. It is global, and as noticed by others, introduces a separate source of maintenance effort. John Papa and Glenn Block have provided an alternative based on MEF that I do have used. The MVVM-Light toolkit does, however, provide a facility to handle events generated by the View, in the ViewModel. This facility is the RelayCommand, an addition to the MVVM-Light Toolkit based on work by Josh Smith.

Ok, only ButtonBase children have commands. For events form other controls you can use the EventTrigger from the Interactivity library for e.g. the Loaded event of the UserControl like so.

    <i:EventTrigger EventName="Loaded">
        <i:InvokeCommandAction Command="{Binding NavigateTo}" commandParameter="NextPage"/>

The NavigateTo command referenced in the code above is implemented as a RelayCommand in the ViewModel. The road from the ViewModel to the View is always by DataBinding


Attaching a ViewModel to a View as a resource preserves Blendability: the possibility to edit the View in Expression Blend, and finding in Blend that the ViewModel is attached as the DataSource and is accessible as such. When using a MEF ViewModel locator following the article by Papa and Block, Blendability is also preserved. Moreover, one of the goodies of using MEF is that the style defined for the App shop automatically permeates through to the Catalogue and its items, to the Master window, and to all the Apps loaded into the Master. Of course locally specified styles are preserved.

Architecture of the App Shop

So, now that we now about the requirements and the technology used, what does the structure of the App Shop looks like?

The portal consists of a main window that holds the logo, which acts as the Home button, and some small buttons, collectively referred to as the “small prints” at the bottom that concern legal aspects, contact information, and maintenance of visitor profiles (to be implemented 🙂 ).

This main window holds at any time one of two components:

– The App Shop Catalogue which presents the available Apps

– The App Master Window that provides a uniform context for all Apps in the shop.


Typically the user selects an App from the catalogue, by clicking on its icon, and the portal navigates to the Master window which loads the selected App. Information concerning the selected App is stored in the application level resource dictionary during transition, which (indeed) is abused as a kind of session variable, much like the Session in ASP.Net.

The Catalogue consists of a number of buttons, each holding an image and a caption identifying the App it represents. The images are loaded from a directory at the web server, the information about the Apps is loaded from an XML file, also at the web server.

To deploy an App, it suffices to add a catalog record to the XML file, to add an image to the image directory and to add the App to the App directory. No recompilation of the portal required. The App needs to have one or more MEF “Export” Attributes added, so has to be rebuilt.

When an App is selected from the catalogue, the Catalogue is unloaded, the Main window loads the Master, and the Master loads the App. The App is retrieved from the web server, at that point and not before. Apps that have been retrieved once are cached by the web browser, as are shared libraries. When preparing an App for use in the portal care is taken not to copy in libraries into the xap file that are already present at the client.


The Binding System

The Blog Post by Papa and Block mentions a bug in the binding system – and provides a work around. The bug has not been resolved yet, at the time of writing this article. The articulation of the bug is incorrect, by the way. The text states that DataBinding will occur at most 6 times. In reality, DataBinding will occur exactly 6 times, for each binding (where 1 time would suffice).


Although Apps can be added to the App Shop without rebuilding and redeploying the entire postal, I find myself doing just that nevertheless. The reason is that I like to keep the portal and Apps source code together in a single solution.

And Now…

Well, now it is easy to maintain and extend the portal, it is time to add Apps, of course, to Load the portal into Expression Blend and give it a much more sophisticated design and User Experience, and to add some more technical features. To be continued!

A Silverlight Deep Zoom Exercise

Silverlight DeepZoom allows you to create a set of (one or more) pictures that load very quickly, and allow for intensive zooming. The technology is based on the creation of a set of images of various resolutions that are being loaded in a sequence from low res to high. This gives you the experience that a picture is loaded in little time, and that the resolution still improves in the few seconds after the picture is first shown. I’ve done an exercise to get the trick into my bag. Doing nothing new, by the way.

But then I wanted to deploy the project onto my test server. That put me in an awkward situation. Silverlight deployment is by Zip files called xap files. If you add the picture collection to the xap, you pass by the intention of DeepZoom that you don’t need to wait for large images to be downloaded before you can see them. So you want to add them to the web application that hosts the Silverlight application. It turned out that WebDeploy overwrites the images every time you redeploy. So the question became: How to add the DeepZoom image collection to the hosting web application in such a way that:

i. The Silverlight application can find it.

ii. WebDeploy deploys it for you.

iii. You don’t deploy it as a resource with your Silverlight application.

The trick that does it is to simply add the directory with the image collection to your hosting web application’s ClientBin directory. Then click the show all files button in your VS2010 project, and finally right click the bleak icon for your image collection and select “Include In Project”. See the screen shots below.

You can play around with the Deep Zoom exercise at my App Shop. Zooming in and out is by rolling your mouse wheel (sorry if you don’t have any 😉 ). Zooming in aims at the mouse pointer location. You can also drag the image around with the mouse and enjoy the nice inertia animation.

Above you see the DZC (Deep Zoom Collection) Source folder represented by bleak icons. Right clicking the Source folder gives you the image below.

Now you can publish your web application safely and easily using WebDeploy.

– Is that all?

– Yes, that’s all.

– But, that’s trivial!

– Yes, it is. But it is also a problem many people struggle hard with, and don’t get it done.

Rotating Video Panel

Posted: February 10, 2011 in Silverlight
Tags: , , ,

Silverlight Sample: Rotating Video Panel

Edit 2011-07-07: A wet floor effect has been added to the app. This includes a two-color background and an upside down reflection of the rotating video. You can check it out at the App Shop .

As an exercise in media handling and animation, I built a rotating video panel. This is not an original work, it is based on the rotating video panel by Sean Christman (CraftyMind), you can find it here (opens a new window or tab). Note that while rotating, texts are mirrored when we look at the rear site of the panel.

To me, it is of some relevance that when migrating someone else’s work to Silverlight, the stone is thrown a bit further. In this particular example the extra distance is small: the rotating panel scales with the size of the window if you change it.

Another nice feature, but that is typically Silverlight, is that you can install this panel on your pc as a small application, and run it offline also. Just right click the rotating panel, choose install from the menu, and follow the instructions. To uninstall it again, run the installed application, click it with your right mouse button, and choose uninstall.

An aspect that presents a nicety for me is that the Silverlight code is much shorter than the 145 lines of Html5 code that were required for the original work. The xaml below is all it takes to realize the rotating video panel, anything above “<Grid.Resources>” is generated code.

<UserControl x:Class="SpinningVideoPanel.MainPage"
    d:DesignHeight="600" d:DesignWidth="600">

    <Grid x:Name="LayoutRoot" Background="White" Margin="150,0,150,150" MinWidth="100" MinHeight="100">
            <Storyboard x:Name="rotationStoryBoard1" RepeatBehavior="Forever"
                        Storyboard.TargetName="rotation1" Storyboard.TargetProperty="RotationY">
                <DoubleAnimation From="0" To="360" Duration="0:0:10"/>
            <BitmapCache RenderAtScale="4" />
            <RowDefinition Height="50*" />
            <RowDefinition Height="175*" />
            <RowDefinition Height="75*" />
            <PlaneProjection RotationY="360" x:Name="rotation1" />
        <Border BorderThickness="5" BorderBrush="Salmon" HorizontalAlignment="Center" VerticalAlignment="Center" >
            <TextBlock Name="textBlock1" Text="Watch the Video" VerticalAlignment="Center" HorizontalAlignment="Center" Margin="5" />
        <Border BorderThickness="1" BorderBrush="Black" Grid.Row="1">
            <MediaElement x:Name="mediaElement1" Source="Silverlight_540p20s.mp4" AutoPlay="True" Grid.Row="1"  Stretch="Fill" MediaEnded="mediaElement1_MediaEnded"/>
        <Rectangle Grid.Row="2" Name="rectangle2" Stroke="Black" StrokeThickness="1" VerticalAlignment="Bottom" Height="1" Margin="0,0,0,20">
                <BlurEffect Radius="3"/>

The C# code below starts and repeats the video.

using System.Windows;
using System.Windows.Controls;

namespace SpinningVideoPanel
    public partial class MainPage : UserControl
        public MainPage()

            Loaded += new RoutedEventHandler(MainPage_Loaded);

        void MainPage_Loaded(object sender, RoutedEventArgs e)

        private void mediaElement1_MediaEnded(object sender, RoutedEventArgs e)

Configuration settings promote GPU utilization, in case a suitable graphics card is present in the client computer.

You can see the rotating video panel in action in my App Shop here.