gecko-dev/gfx/webrender/res/ps_radial_gradient.fs.glsl

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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
uniform sampler2D sGradients;
void main(void) {
vec2 cd = vEndCenter - vStartCenter;
vec2 pd = vPos - vStartCenter;
float rd = vEndRadius - vStartRadius;
// Solve for t in length(t * cd - pd) = vStartRadius + t * rd
// using a quadratic equation in form of At^2 - 2Bt + C = 0
float A = dot(cd, cd) - rd * rd;
float B = dot(pd, cd) + vStartRadius * rd;
float C = dot(pd, pd) - vStartRadius * vStartRadius;
float x;
if (A == 0.0) {
// Since A is 0, just solve for -2Bt + C = 0
if (B == 0.0) {
discard;
}
float t = 0.5 * C / B;
if (vStartRadius + rd * t >= 0.0) {
x = t;
} else {
discard;
}
} else {
float discr = B * B - A * C;
if (discr < 0.0) {
discard;
}
discr = sqrt(discr);
float t0 = (B + discr) / A;
float t1 = (B - discr) / A;
if (vStartRadius + rd * t0 >= 0.0) {
x = t0;
} else if (vStartRadius + rd * t1 >= 0.0) {
x = t1;
} else {
discard;
}
}
vec2 texture_size = vec2(textureSize(sGradients, 0));
// Either saturate or modulo the offset depending on repeat mode, then scale to number of
// gradient color entries (texture width / 2).
x = mix(clamp(x, 0.0, 1.0), fract(x), vGradientRepeat) * 0.5 * texture_size.x;
// Start at the center of first color in the nearest 2-color entry, then offset with the
// fractional remainder to interpolate between the colors. Rely on texture clamping when
// outside of valid range.
x = 2.0 * floor(x) + 0.5 + fract(x);
// Normalize the texture coordates so we can use texture() for bilinear filtering.
oFragColor = texture(sGradients, vec2(x, vGradientIndex) / texture_size);
}