>Psychtoolbox>PsychGLImageProcessing

[noiseid, noiserect] = CreateProceduralNoise(windowPtr, width, height [, noiseType=’ClassicPerlin’][, backgroundColorOffset =(0,0,0,0)][, param1][, param2, …])

Creates a procedural texture that allows to draw random noise stimulus patches
in a very fast and efficient manner on modern graphics hardware.

This works on GPU’s with support for the OpenGL shading language and
vertex- and fragment shaders. See ProceduralNoiseDemo for examples on how to use this function.

Parameters and their meaning:

‘windowPtr’ A handle to the onscreen window.

‘width’ x ‘height’ The maximum 2D size (in pixels) of the noise patch.

‘noiseType’ Name of the noise function to use, defaults to ‘ClassicPerlin’.
The following types of noise are currently supported:

• ‘Perlin’: Generates Perlin noise, which is approximately gaussian
  distributed.

• ‘ClassicPerlin’: Like Perlin, but with the classic implementation.

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

‘param1’ … ‘paramN’ - Parameters specific to the noise function.

The function returns a procedural texture handle ‘noiseid’ that you can
pass to the Screen(‘DrawTexture(s)’, windowPtr, noiseid, …) functions
like any other texture handle. The ‘noiserect’ is a rectangle which
describes the size of the noise texture support.

A typical invocation to draw a single noise patch may look like this:

Screen(‘DrawTexture’, windowPtr, noiseid, [], dstRect, [], [], [],
modulateColor, [], [], [contrast, seed, 0, 0]);

Draws the patch ‘noiseid’ into window ‘windowPtr’, at position ‘dstRect’,
or in the center if ‘dstRect’ is set to []. Make sure ‘dstRect’ has the
size of ‘noiserect’ to avoid spatial distortions! You could do, e.g.,
dstRect = OffsetRect(noiserect, xc, yc) to place the patch centered at
screen position (xc,yc).

‘modulateColor’ is the base color of the noise patch - it defaults to
white, ie. the noise has only luminance, but no color. If you’d set it to
[255 0 0] you’d get a reddish noise.

‘contrast’ is the amplitude of your patch in intensity units - A factor
that is multiplied to the random number before converting the
value into a color value. ‘contrast’ may be a bit of a misleading term
here…

‘seed’ Defines the random seed for drawing of a pseudo-random patch.

Make sure to use the Screen(‘DrawTextures’, …); function properly,
instead of the Screen(‘DrawTexture’, …); function, if you want to draw
many different patches simultaneously - this is much faster!