src/gpu/glsl/GrGLSLXferProcessor.cpp

/*
 * Copyright 2014 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "src/gpu/glsl/GrGLSLXferProcessor.h"

#include "src/gpu/GrShaderCaps.h"
#include "src/gpu/GrTexture.h"
#include "src/gpu/GrXferProcessor.h"
#include "src/gpu/glsl/GrGLSLFragmentShaderBuilder.h"
#include "src/gpu/glsl/GrGLSLProgramDataManager.h"
#include "src/gpu/glsl/GrGLSLUniformHandler.h"

// This is only called for cases where we are doing LCD coverage and not using in shader blending.
// For these cases we assume the the src alpha is 1, thus we can just use the max for the alpha
// coverage since src alpha will always be greater than or equal to dst alpha.
static void adjust_for_lcd_coverage(GrGLSLXPFragmentBuilder* fragBuilder,
                                    const char* srcCoverage,
                                    const GrXferProcessor& proc) {
    if (srcCoverage && proc.isLCD()) {
        fragBuilder->codeAppendf("%s.a = max(max(%s.r, %s.g), %s.b);",
                                 srcCoverage, srcCoverage, srcCoverage, srcCoverage);
    }
}

void GrGLSLXferProcessor::emitCode(const EmitArgs& args) {
    if (!args.fXP.willReadDstColor()) {
        adjust_for_lcd_coverage(args.fXPFragBuilder, args.fInputCoverage, args.fXP);
        this->emitOutputsForBlendState(args);
    } else {
        GrGLSLXPFragmentBuilder* fragBuilder = args.fXPFragBuilder;
        GrGLSLUniformHandler* uniformHandler = args.fUniformHandler;
        const char* dstColor = fragBuilder->dstColor();

        bool needsLocalOutColor = false;

        if (args.fDstTextureSamplerHandle.isValid()) {
            if (args.fInputCoverage) {
                // We don't think any shaders actually output negative coverage, but just as a
                // safety check for floating point precision errors, we compare with <= here. We
                // just check the RGB values of the coverage, since the alpha may not have been set
                // when using LCD. If we are using single-channel coverage, alpha will be equal to
                // RGB anyway.
                //
                // The discard here also helps for batching text-draws together, which need to read
                // from a dst copy for blends. However, this only helps the case where the outer
                // bounding boxes of each letter overlap and not two actually parts of the text.
                fragBuilder->codeAppendf("if (all(lessThanEqual(%s.rgb, half3(0)))) {"
                                         "    discard;"
                                         "}", args.fInputCoverage);
            }
        } else {
            needsLocalOutColor = args.fShaderCaps->requiresLocalOutputColorForFBFetch();
        }

        const char* outColor = "_localColorOut";
        if (!needsLocalOutColor) {
            outColor = args.fOutputPrimary;
        } else {
            fragBuilder->codeAppendf("half4 %s;", outColor);
        }

        this->emitBlendCodeForDstRead(fragBuilder,
                                      uniformHandler,
                                      args.fInputColor,
                                      args.fInputCoverage,
                                      dstColor,
                                      outColor,
                                      args.fOutputSecondary,
                                      args.fXP);
        if (needsLocalOutColor) {
            fragBuilder->codeAppendf("%s = %s;", args.fOutputPrimary, outColor);
        }
    }

    // Swizzle the fragment shader outputs if necessary.
    this->emitWriteSwizzle(args.fXPFragBuilder, args.fWriteSwizzle, args.fOutputPrimary,
                           args.fOutputSecondary);
}

void GrGLSLXferProcessor::emitWriteSwizzle(GrGLSLXPFragmentBuilder* x,
                                           const GrSwizzle& swizzle,
                                           const char* outColor,
                                           const char* outColorSecondary) const {
    if (GrSwizzle::RGBA() != swizzle) {
        x->codeAppendf("%s = %s.%s;", outColor, outColor, swizzle.asString().c_str());
        if (outColorSecondary) {
            x->codeAppendf("%s = %s.%s;", outColorSecondary, outColorSecondary,
                           swizzle.asString().c_str());
        }
    }
}

void GrGLSLXferProcessor::setData(const GrGLSLProgramDataManager& pdm, const GrXferProcessor& xp) {
    this->onSetData(pdm, xp);
}

void GrGLSLXferProcessor::DefaultCoverageModulation(GrGLSLXPFragmentBuilder* fragBuilder,
                                                    const char* srcCoverage,
                                                    const char* dstColor,
                                                    const char* outColor,
                                                    const char* outColorSecondary,
                                                    const GrXferProcessor& proc) {
    if (srcCoverage) {
        if (proc.isLCD()) {
            fragBuilder->codeAppendf("half3 lerpRGB = mix(%s.aaa, %s.aaa, %s.rgb);",
                                     dstColor, outColor, srcCoverage);
        }
        fragBuilder->codeAppendf("%s = %s * %s + (half4(1.0) - %s) * %s;",
                                 outColor, srcCoverage, outColor, srcCoverage, dstColor);
        if (proc.isLCD()) {
            fragBuilder->codeAppendf("%s.a = max(max(lerpRGB.r, lerpRGB.b), lerpRGB.g);", outColor);
        }
    }
}