src/gpu/gradients/GrTiledGradientEffect.fp

/*
 * Copyright 2018 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

// Provides tiling for the repeat or mirror modes.

in fragmentProcessor colorizer;
in fragmentProcessor gradLayout;

layout(key) in bool mirror;
layout(key) in bool makePremul;
// Trust the creator that this matches the color spec of the gradient
in bool colorsAreOpaque;
layout(key) in bool layoutPreservesOpacity;

half4 main() {
    half4 t = sample(gradLayout);

    if (!layoutPreservesOpacity && t.y < 0) {
        // layout has rejected this fragment (rely on sksl to remove this branch if the layout FP
        // preserves opacity is false)
        return half4(0);
    } else {
        @if (mirror) {
            half t_1 = t.x - 1;
            half tiled_t = t_1 - 2 * floor(t_1 * 0.5) - 1;
            if (sk_Caps.mustDoOpBetweenFloorAndAbs) {
                // At this point the expected value of tiled_t should between -1 and 1, so this
                // clamp has no effect other than to break up the floor and abs calls and make sure
                // the compiler doesn't merge them back together.
                tiled_t = clamp(tiled_t, -1, 1);
            }
            t.x = abs(tiled_t);
        } else {
            // Simple repeat mode
            t.x = fract(t.x);
        }

        // Always sample from (x, 0), discarding y, since the layout FP can use y as a side-channel.
        @if (!makePremul) {
            return sample(colorizer, t.x0);
        } else {
            half4 outColor = sample(colorizer, t.x0);
            return outColor * outColor.aaa1;
        }
    }
}

//////////////////////////////////////////////////////////////////////////////

// If the layout does not preserve opacity, remove the opaque optimization,
// but otherwise respect the provided color opacity state.
@optimizationFlags {
    kCompatibleWithCoverageAsAlpha_OptimizationFlag |
    (colorsAreOpaque && layoutPreservesOpacity ? kPreservesOpaqueInput_OptimizationFlag
                                               : kNone_OptimizationFlags)
}

@make{
    static std::unique_ptr<GrFragmentProcessor> Make(
            std::unique_ptr<GrFragmentProcessor> colorizer,
            std::unique_ptr<GrFragmentProcessor> gradLayout,
            bool mirror,
            bool makePremul,
            bool colorsAreOpaque) {
        bool layoutPreservesOpacity = gradLayout->preservesOpaqueInput();
        return std::unique_ptr<GrFragmentProcessor>(new GrTiledGradientEffect(
                std::move(colorizer), std::move(gradLayout), mirror, makePremul, colorsAreOpaque,
                layoutPreservesOpacity));
    }
}