libs/hwui/renderstate/Blend.cpp

/*
 * Copyright (C) 2015 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#include <renderstate/Blend.h>
#include "Program.h"

namespace android {
namespace uirenderer {

/**
 * Structure mapping Skia xfermodes to OpenGL blending factors.
 */
struct Blender {
    SkBlendMode mode;
    GLenum src;
    GLenum dst;
};

// assumptions made by lookup tables in either this file or ProgramCache
static_assert(0 == static_cast<int>(SkBlendMode::kClear), "SkBlendMode enums have changed");
static_assert(1 == static_cast<int>(SkBlendMode::kSrc), "SkBlendMode enums have changed");
static_assert(2 == static_cast<int>(SkBlendMode::kDst), "SkBlendMode enums have changed");
static_assert(3 == static_cast<int>(SkBlendMode::kSrcOver), "SkBlendMode enums have changed");
static_assert(4 == static_cast<int>(SkBlendMode::kDstOver), "SkBlendMode enums have changed");
static_assert(5 == static_cast<int>(SkBlendMode::kSrcIn), "SkBlendMode enums have changed");
static_assert(6 == static_cast<int>(SkBlendMode::kDstIn), "SkBlendMode enums have changed");
static_assert(7 == static_cast<int>(SkBlendMode::kSrcOut), "SkBlendMode enums have changed");
static_assert(8 == static_cast<int>(SkBlendMode::kDstOut), "SkBlendMode enums have changed");
static_assert(9 == static_cast<int>(SkBlendMode::kSrcATop), "SkBlendMode enums have changed");
static_assert(10 == static_cast<int>(SkBlendMode::kDstATop), "SkBlendMode enums have changed");
static_assert(11 == static_cast<int>(SkBlendMode::kXor), "SkBlendMode enums have changed");
static_assert(12 == static_cast<int>(SkBlendMode::kPlus), "SkBlendMode enums have changed");
static_assert(13 == static_cast<int>(SkBlendMode::kModulate), "SkBlendMode enums have changed");
static_assert(14 == static_cast<int>(SkBlendMode::kScreen), "SkBlendMode enums have changed");
static_assert(15 == static_cast<int>(SkBlendMode::kOverlay), "SkBlendMode enums have changed");
static_assert(16 == static_cast<int>(SkBlendMode::kDarken), "SkBlendMode enums have changed");
static_assert(17 == static_cast<int>(SkBlendMode::kLighten), "SkBlendMode enums have changed");

// In this array, the index of each Blender equals the value of the first
// entry. For instance, gBlends[1] == gBlends[SkBlendMode::kSrc]
const Blender kBlends[] = {{SkBlendMode::kClear, GL_ZERO, GL_ONE_MINUS_SRC_ALPHA},
                           {SkBlendMode::kSrc, GL_ONE, GL_ZERO},
                           {SkBlendMode::kDst, GL_ZERO, GL_ONE},
                           {SkBlendMode::kSrcOver, GL_ONE, GL_ONE_MINUS_SRC_ALPHA},
                           {SkBlendMode::kDstOver, GL_ONE_MINUS_DST_ALPHA, GL_ONE},
                           {SkBlendMode::kSrcIn, GL_DST_ALPHA, GL_ZERO},
                           {SkBlendMode::kDstIn, GL_ZERO, GL_SRC_ALPHA},
                           {SkBlendMode::kSrcOut, GL_ONE_MINUS_DST_ALPHA, GL_ZERO},
                           {SkBlendMode::kDstOut, GL_ZERO, GL_ONE_MINUS_SRC_ALPHA},
                           {SkBlendMode::kSrcATop, GL_DST_ALPHA, GL_ONE_MINUS_SRC_ALPHA},
                           {SkBlendMode::kDstATop, GL_ONE_MINUS_DST_ALPHA, GL_SRC_ALPHA},
                           {SkBlendMode::kXor, GL_ONE_MINUS_DST_ALPHA, GL_ONE_MINUS_SRC_ALPHA},
                           {SkBlendMode::kPlus, GL_ONE, GL_ONE},
                           {SkBlendMode::kModulate, GL_ZERO, GL_SRC_COLOR},
                           {SkBlendMode::kScreen, GL_ONE, GL_ONE_MINUS_SRC_COLOR}};

// This array contains the swapped version of each SkBlendMode. For instance
// this array's SrcOver blending mode is actually DstOver. You can refer to
// createLayer() for more information on the purpose of this array.
const Blender kBlendsSwap[] = {{SkBlendMode::kClear, GL_ONE_MINUS_DST_ALPHA, GL_ZERO},
                               {SkBlendMode::kSrc, GL_ZERO, GL_ONE},
                               {SkBlendMode::kDst, GL_ONE, GL_ZERO},
                               {SkBlendMode::kSrcOver, GL_ONE_MINUS_DST_ALPHA, GL_ONE},
                               {SkBlendMode::kDstOver, GL_ONE, GL_ONE_MINUS_SRC_ALPHA},
                               {SkBlendMode::kSrcIn, GL_ZERO, GL_SRC_ALPHA},
                               {SkBlendMode::kDstIn, GL_DST_ALPHA, GL_ZERO},
                               {SkBlendMode::kSrcOut, GL_ZERO, GL_ONE_MINUS_SRC_ALPHA},
                               {SkBlendMode::kDstOut, GL_ONE_MINUS_DST_ALPHA, GL_ZERO},
                               {SkBlendMode::kSrcATop, GL_ONE_MINUS_DST_ALPHA, GL_SRC_ALPHA},
                               {SkBlendMode::kDstATop, GL_DST_ALPHA, GL_ONE_MINUS_SRC_ALPHA},
                               {SkBlendMode::kXor, GL_ONE_MINUS_DST_ALPHA, GL_ONE_MINUS_SRC_ALPHA},
                               {SkBlendMode::kPlus, GL_ONE, GL_ONE},
                               {SkBlendMode::kModulate, GL_DST_COLOR, GL_ZERO},
                               {SkBlendMode::kScreen, GL_ONE_MINUS_DST_COLOR, GL_ONE}};

Blend::Blend() : mEnabled(false), mSrcMode(GL_ZERO), mDstMode(GL_ZERO) {
    // gl blending off by default
}

void Blend::invalidate() {
    syncEnabled();
    mSrcMode = mDstMode = GL_ZERO;
}

void Blend::syncEnabled() {
    if (mEnabled) {
        glEnable(GL_BLEND);
    } else {
        glDisable(GL_BLEND);
    }
}

void Blend::getFactors(SkBlendMode mode, ModeOrderSwap modeUsage, GLenum* outSrc, GLenum* outDst) {
    int index = static_cast<int>(mode);
    *outSrc = (modeUsage == ModeOrderSwap::Swap) ? kBlendsSwap[index].src : kBlends[index].src;
    *outDst = (modeUsage == ModeOrderSwap::Swap) ? kBlendsSwap[index].dst : kBlends[index].dst;
}

void Blend::setFactors(GLenum srcMode, GLenum dstMode) {
    if ((srcMode == GL_ZERO || srcMode == GL_ONE) && dstMode == GL_ZERO) {
        // disable blending
        if (mEnabled) {
            glDisable(GL_BLEND);
            mEnabled = false;
        }
    } else {
        // enable blending
        if (!mEnabled) {
            glEnable(GL_BLEND);
            mEnabled = true;
        }

        if (srcMode != mSrcMode || dstMode != mDstMode) {
            glBlendFunc(srcMode, dstMode);
            mSrcMode = srcMode;
            mDstMode = dstMode;
        }
    }
}

void Blend::dump() {
    ALOGD("Blend: enabled %d, func src %d, dst %d", mEnabled, mSrcMode, mDstMode);
}

} /* namespace uirenderer */
} /* namespace android */