MakeTextureDrawShader

Psychtoolbox › PsychGLImageProcessing

glsl = MakeTextureDrawShader(windowPtr, shadertype [, backgroundColorOffset = [0,0,0,0]]);

Create a special GLSL shader that can apply some special image processing
operations that modify the normal drawing of textures via
Screen('DrawTexture(s)'). Return a handle 'glsl' to the shader.

The created shader can be attached to specific textures via passing the
returned 'glsl' argument as the optional 'textureShader' argument for the
Screen('MakeTexture', ....., textureShader); function. It can be also
applied on a per-draw basis by passing the 'glsl' handle as optional
'textureShader' argument to the Screen('DrawTexture(s)', ...); function.

Mandatory arguments:

'windowPtr' A handle to the onscreen window to which the shader should be
associated.

'shadertype' A name string that defines the type of shader / image
processing operation to apply. It can be one of the following:

- 'SeparateAlphaChannel': Alpha values are looked up at the regular
locations defined via the 'srcRect' parameter in a Screen('DrawTexture')
call. RGB color values are looked up at srcRect, offset by some (dx,dy)
offset, as provided by the 'auxParameters' vector [dx, dy, 0, 0].
Providing non-zero offset values for dx and dy allows to "shift" or
"scroll" the RGB or Luminance image inside a texture during drawing,
while keeping the alpha image at a fixed location, solely defined by
'srcRect'. This is mostly useful if you want to draw some drifting
stimulus with a fixed alpha channel mask applied, ie., the color image
should move, but the alpha mask should stay fixed.

- 'PremultipliedAlphaChannel': Like 'SeparateAlphaChannel', but the alpha
value is not written to the framebuffer, but premultiplied to the RGB
color pixel before writeout.

'backgroundColorOffset' Optional, defaults to [0 0 0 0]. A RGBA offset
color to add to the final RGBA colors of the drawn texture, prior to
drawing it.