>Psychtoolbox>PsychGLImageProcessing

[id, rect, shader] = CreateProceduralColorGrating(windowPtr, width,
height [, color1=[1 0 0]] [, color2=[0 1 0]] [, radius=0])

A procedural color grating shader that can generate either sinusoidal or
square gratings varying between two colors.

INPUT VALUES:

* width, height = “virtual size” of the GLSL shader.
* color1, color2 = two colors for the grating peaks to vary between. When
running (see ProceduralColorGratingDemo)), you can pass baseColor parameter,
from which color1 and color2 will be modulated via the contrast parameter.
When contrast is 0, then color1 and color2 are the same as baseColor. As
contrast increases each color is mixed with baseColor until at contrast 1
the grating peaks are color1 and color2 exactly. Color mixing uses
OpenGL’s mix command.
* radius = optional hard-edged circular mask sized in pixels.

RETURN VALUES:

* id = texture pointer.
* rect = rect describing the size and shape of the texture.
* shader = the GLSL shader, useful if you want to use glUniform commands to
modify color 1, color2 or radius after texture creation.

DRAWING MODIFIERS:

When drawing this shader using Screen(‘DrawTexture|s’), you can pass
additional values:

* baseColor is the base color from which color1 and color2 are mixed.
* contrast is the mixing amount from baseColor to color1 and color2.
* sigma is a smoothing value, when sigma == -1 a sinusoidal grating is
produced; and when sigma >= 0 a square wave grating is produced using sigma
value of smoothing at the edge.

TEXTURE DETAILS:

Color blending (blending each color to the baseColor, and then blending
with each other) uses GLSL mix function; mix performs a linear
interpolation between x and y using a to weight between them. The return
value is computed as: $x \times (1 - a) + y \times a$. See
http://docs.gl/sl4/mix\ for more details.

Smoothing uses GLSL smoothstep function that uses hermite interpolation.
A small amount of smoothing for squarewave grating edges can reduce
jumping artifacts when squarewave gratings are drifted. See
http://docs.gl/sl4/smoothstep\ for more details.

See also: CreateProceduralSineGrating, CreateProceduralSineSquareGrating