/* 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/. */
// Gradient GPU cache address.
// Packed in to a vector to work around bug 1630356.
flat varying highp ivec2 v_gradient_address;
// Repetition along the gradient stops.
// Packed in to a vector to work around bug 1630356.
flat varying mediump vec2 v_gradient_repeat;
#ifdef WR_FRAGMENT_SHADER
#ifdef WR_FEATURE_DITHERING
vec4 dither(vec4 color) {
const int matrix_mask = 7;
ivec2 pos = ivec2(gl_FragCoord.xy) & ivec2(matrix_mask);
float noise_normalized = (texelFetch(sDither, pos, 0).r * 255.0 + 0.5) / 64.0;
float noise = (noise_normalized - 0.5) / 256.0; // scale down to the unit length
return color + vec4(noise, noise, noise, 0);
}
#else
vec4 dither(vec4 color) {
return color;
}
#endif //WR_FEATURE_DITHERING
#define GRADIENT_ENTRIES 128.0
float clamp_gradient_entry(float offset) {
// Calculate the color entry index to use for this offset:
// offsets < 0 use the first color entry, 0
// offsets from [0, 1) use the color entries in the range of [1, N-1)
// offsets >= 1 use the last color entry, N-1
// so transform the range [0, 1) -> [1, N-1)
// TODO(gw): In the future we might consider making the size of the
// LUT vary based on number / distribution of stops in the gradient.
// Ensure we don't fetch outside the valid range of the LUT.
return clamp(1.0 + offset * GRADIENT_ENTRIES, 0.0, 1.0 + GRADIENT_ENTRIES);
}
vec4 sample_gradient(float offset) {
// Modulo the offset if the gradient repeats.
offset -= floor(offset) * v_gradient_repeat.x;
// Calculate the texel to index into the gradient color entries:
// floor(x) is the gradient color entry index
// fract(x) is the linear filtering factor between start and end
float x = clamp_gradient_entry(offset);
float entry_index = floor(x);
float entry_fract = x - entry_index;
// Fetch the start and end color. There is a [start, end] color per entry.
vec4 texels[2] = fetch_from_gpu_buffer_2f(v_gradient_address.x + 2 * int(entry_index));
// Finally interpolate and apply dithering
return dither(texels[0] + texels[1] * entry_fract);
}
#endif //WR_FRAGMENT_SHADER
