1 files changed, 63 insertions, 0 deletions
diff --git a/gfx/wr/webrender/res/gradient.glsl b/gfx/wr/webrender/res/gradient.glsl
new file mode 100644
index 0000000000..103059fdf9
--- /dev/null
+++ b/gfx/wr/webrender/res/gradient.glsl
@@ -0,0 +1,63 @@
+/* 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_FS_ADDRESS ivec2 v_gradient_address;
+// Repetition along the gradient stops.
+// Packed in to a vector to work around bug 1630356.
+flat varying 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_2(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