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/* ExpandingRings shader
* Draws a sequence of rings of alternating color. The center
* of all rings is assigned in 'RingCenter' by the Matlab script,
* width of a ring is assigned in 'RingWidth', the radius of the
* outermost ring is assigned in 'Radius', a shift (scrolling offset)
* is assigned in 'Shift'. See ExpandingRingsDemo.m for explanation.
*
*
* Written 2007 by Mario Kleiner, licensed to you under MIT license.
*/
#version 110
uniform vec2 RingCenter;
/* Values passed from vertex shader: */
varying float RingWidth;
varying float Radius;
varying float Shift;
varying vec4 firstColor;
varying vec4 secondColor;
void main()
{
/* Query current output texel position: */
vec2 pos = gl_TexCoord[0].xy;
/* Compute euclidean distance to center of our ring stim: */
float d = distance(pos, RingCenter);
/* If distance greater than maximum radius, discard this pixel: */
if (d > Radius) discard;
/* Convert distance from units of pixels into units of ringwidths, apply shift offset: */
d = floor((d - Shift) / RingWidth);
/* A pixel in an even-numbered ring is drawn in gl_Color, the color assigned in the */
/* Screen('DrawTexture') command as modulateColor, whereas a pixel in an odd-numbered */
/* ring is assigned 'secondColor': */
gl_FragColor = mix(firstColor, secondColor, mod(d,2.0));
}
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