HLSL and Pixel Shaders for XAML Developers

Chapter 8. The Zen of Shader Programming

Zen of Pixel Programming

Now that you have the HLSL language concepts firmly in hand, let’s consider how to use them in common scenarios. This final chapter explores the essential subjects that every shader developer needs to know.

Sampling a Pixel Color

Examine the main function signature in any shader code (Example 8-1).

Example 8-1. Sampling pixel color in shader

sampler2D input : register(S0);
float4 main(float2 uv : TEXCOORD) : COLOR
{

  float4 color;
  color= tex2D( input , uv.xy);

  return color;
}

The parameter passed into the function is typed as float2. It represents the x and y coordinates of the current pixel. As each pixel is processed by the shader, the float2 parameter provides access to the current location. So what do you do with that information?

A common task is to use the coordinate to determine the current pixel color. To accomplish this task requires the talents of the tex2D function. I looked up the definition of the text2D function in the DirectX documentation and it states:

“Samples a 2D texture.”

If the documentation writer was looking to accolades for the shortest answer, this little nugget is a prizewinner. Short, maybe, but not very useful. Let me try.

The tex2D function performs a texture lookup. In other words, it examines a given texture (a pointer to an image) and returns the color value at the specified location. There are other texture functions (tex1D and tex3D) available, but for now we’ll stay with the 2D version. The ...