Code_for_developing_Lightworks_effects

Here we collect code to create Lightworks.fx effects.

View project on GitHub

Shaders

Example of a simple shader

This code rotates the texture by 180 °:

float4 ps_main (float2 uv : TEXCOORD1) : COLOR 
{ 
   return tex2D (InputSampler, 1.0 - uv); 
}

Name of the Pixel Shaders:

float4 ps_main We recommend using the prefix ps_ for each shader, which makes it clear what it is.
In the example above ps_main.
Note: This name must also be entered outside the shader in the corresponding entry in the “Techniques” section.

Texture coordinates:

float4 ps_main (float2 uv : TEXCOORD1) : COLOR`

The (float2 uv : TEXCOORD1) inside the parenthesis defines uv to be the coordinates of the texture.
This float2 variable contains the components x and y that determine the position of the output texel to be calculated.
Because the texture consists of many texels, uv will assume different values.
(float2 uv: TEXCOORD1) causes the GPU to do this fully automatically.

more details

Description of the above example code:

    return tex2D (InputSampler, 1.0 - uv);
  • return expects a float4 RGBA value, which is returned to the “Techniques”.
  • tex2D (.. is a function call. This standard CG function is already implemented globally for all effects.
  • InputSampler, It is the first parameter passed to the tex2D function. The sampler specified here must exist outside the shader, further up in the effect code. This sampler will read and preprocess the RGBA value of a texture.
  • 1.0 - uv The result of this calculation is the second parameter passed to the tex2D function and thus also to the sampler. This float2 value tells the samper the sample position. Because this calculation deviates the sampler position from the position of the output pixel, the rotation is achieved at 180 °. This is done by mirroring the texture on both the right and bottom edge of the frame.
    • 1.0 This value corresponds to the right frame edge and the bottom frame edge. details
    • - uv For details about this position variable, see above.

Take parameters from the “Technique”:

jwrl wrote:

[…] you can also pass parameters other than texture coordinates to your shaders.
Here’s an example from my SuperBlur effect.
This does five passes through the same shader, each time with different parameters.

float4 ps_main (float2 uv : TEXCOORD1, uniform sampler blurSampler, uniform float blurRadius) : COLOR

These parameters (the actual sampler name and the variable value) must be entered in the “Techniques”.

For more information see lwks.com post # 147395 on page 5

Programming and GPU load or shader limits:

jwrl wrote:

Also conditional statements aren’t particularly efficient.
They will always carry out both branches of the condition, then discard the result they don’t need. For this reason I will usually try and structure them so that I can force an exit as the sole result of the true condition. In normal programming this is definitely not the best practice, but here it’s a good idea if you can do it. It also means that there is no else condition.

Finally loops will always be unrolled at compile time at least in the Windows compiler. I’m unsure about that for the other two. This has implications for just how much you can build into a loop.