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manual derivatives calculation for radial stim;

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lgtst 2022-10-07 23:21:31 +01:00
parent 934d5c91a7
commit 0d9ca6ba14
2 changed files with 14 additions and 6 deletions
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4
src/visual/GratingStim.js
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@ -2,7 +2,7 @@
* Grating Stimulus.
*
* @author Nikita Agafonov
* @version 2021.2.3
* @version 2022.3.0
* @copyright (c) 2017-2020 Ilixa Ltd. (http://ilixa.com) (c) 2020-2022 Open Science Tools Ltd. (https://opensciencetools.org)
* @license Distributed under the terms of the MIT License
*/
@ -380,6 +380,8 @@ export class GratingStim extends VisualStim
shader: radialStimWGL1,
uniforms: {
uFreq: 20.0,
uStep: .0017,
uDX: 1.,
uPhase: 0.0,
uColor: [1., 1., 1.],
uAlpha: 1.0

16
src/visual/shaders/wgl1/radialShader.frag
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@ -7,7 +7,6 @@
* @description Creates 2d radial grating image. Based on https://www.shadertoy.com/view/wtjGzt
* @usedby GratingStim.js
*/
precision mediump float;
varying vec2 vUvs;
@ -16,20 +15,27 @@ uniform float uFreq;
uniform float uPhase;
uniform vec3 uColor;
uniform float uAlpha;
uniform float uStep;
uniform float uDX;
#define M_PI 3.14159265358979
#define PI2 2.* M_PI
float aastep(float x) { // --- antialiased step(.5)
float w = fwidth(x); // pixel width. NB: x must not be discontinuous or factor discont out
float aastep(float x, float w) { // --- antialiased step(.5)
return smoothstep(.7,-.7,(abs(fract(x-.25)-.5)-.25)/w); // just use (offseted) smooth squares
}
void main() {
vec2 uv = vUvs * 2. - 1.;
float v = uFreq * atan(uv.y, uv.x) / 6.28;
// WGL1 has dFdx, dFdy and fwidth() defined as part of OES_standard_derivatives extension.
// BUT using this extension fails due to how currently used version of PIXI goes about shader program compilation.
// Calculating derivatives manually instead.
float dF_dx = (uFreq * (atan(uv.y, uv.x + uStep) - atan(uv.y, uv.x - uStep)) / 6.28) / uDX;
float dF_dy = (uFreq * (atan(uv.y + uStep, uv.x) - atan(uv.y - uStep, uv.x)) / 6.28) / uDX;
float w = abs(dF_dx) + abs(dF_dy);
// converting first to [-1, 1] space to get the proper color functionality
// then back to [0, 1]
float v = uFreq * atan(uv.y, uv.x) / 6.28;
float s = aastep(v) * 2. - 1.;
float s = aastep(v, w) * 2. - 1.;
gl_FragColor = vec4(vec3(s) * uColor * .5 + .5, 1.0) * uAlpha;
}