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"

#include "ShadowTessellator.h"

namespace android {
namespace uirenderer {

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

// In this array, the index of each Blender equals the value of the first
// entry. For instance, gBlends[1] == gBlends[SkXfermode::kSrc_Mode]
const Blender kBlends[] = {
    { SkXfermode::kClear_Mode,    GL_ZERO,                GL_ONE_MINUS_SRC_ALPHA },
    { SkXfermode::kSrc_Mode,      GL_ONE,                 GL_ZERO },
    { SkXfermode::kDst_Mode,      GL_ZERO,                GL_ONE },
    { SkXfermode::kSrcOver_Mode,  GL_ONE,                 GL_ONE_MINUS_SRC_ALPHA },
    { SkXfermode::kDstOver_Mode,  GL_ONE_MINUS_DST_ALPHA, GL_ONE },
    { SkXfermode::kSrcIn_Mode,    GL_DST_ALPHA,           GL_ZERO },
    { SkXfermode::kDstIn_Mode,    GL_ZERO,                GL_SRC_ALPHA },
    { SkXfermode::kSrcOut_Mode,   GL_ONE_MINUS_DST_ALPHA, GL_ZERO },
    { SkXfermode::kDstOut_Mode,   GL_ZERO,                GL_ONE_MINUS_SRC_ALPHA },
    { SkXfermode::kSrcATop_Mode,  GL_DST_ALPHA,           GL_ONE_MINUS_SRC_ALPHA },
    { SkXfermode::kDstATop_Mode,  GL_ONE_MINUS_DST_ALPHA, GL_SRC_ALPHA },
    { SkXfermode::kXor_Mode,      GL_ONE_MINUS_DST_ALPHA, GL_ONE_MINUS_SRC_ALPHA },
    { SkXfermode::kPlus_Mode,     GL_ONE,                 GL_ONE },
    { SkXfermode::kModulate_Mode, GL_ZERO,                GL_SRC_COLOR },
    { SkXfermode::kScreen_Mode,   GL_ONE,                 GL_ONE_MINUS_SRC_COLOR }
};

// This array contains the swapped version of each SkXfermode. 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[] = {
    { SkXfermode::kClear_Mode,    GL_ONE_MINUS_DST_ALPHA, GL_ZERO },
    { SkXfermode::kSrc_Mode,      GL_ZERO,                GL_ONE },
    { SkXfermode::kDst_Mode,      GL_ONE,                 GL_ZERO },
    { SkXfermode::kSrcOver_Mode,  GL_ONE_MINUS_DST_ALPHA, GL_ONE },
    { SkXfermode::kDstOver_Mode,  GL_ONE,                 GL_ONE_MINUS_SRC_ALPHA },
    { SkXfermode::kSrcIn_Mode,    GL_ZERO,                GL_SRC_ALPHA },
    { SkXfermode::kDstIn_Mode,    GL_DST_ALPHA,           GL_ZERO },
    { SkXfermode::kSrcOut_Mode,   GL_ZERO,                GL_ONE_MINUS_SRC_ALPHA },
    { SkXfermode::kDstOut_Mode,   GL_ONE_MINUS_DST_ALPHA, GL_ZERO },
    { SkXfermode::kSrcATop_Mode,  GL_ONE_MINUS_DST_ALPHA, GL_SRC_ALPHA },
    { SkXfermode::kDstATop_Mode,  GL_DST_ALPHA,           GL_ONE_MINUS_SRC_ALPHA },
    { SkXfermode::kXor_Mode,      GL_ONE_MINUS_DST_ALPHA, GL_ONE_MINUS_SRC_ALPHA },
    { SkXfermode::kPlus_Mode,     GL_ONE,                 GL_ONE },
    { SkXfermode::kModulate_Mode, GL_DST_COLOR,           GL_ZERO },
    { SkXfermode::kScreen_Mode,   GL_ONE_MINUS_DST_COLOR, GL_ONE }
};

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

void Blend::enable(SkXfermode::Mode mode, bool swapSrcDst) {
    GLenum srcMode;
    GLenum dstMode;
    getFactors(mode, swapSrcDst, &srcMode, &dstMode);
    setFactors(srcMode, dstMode);
}

void Blend::disable() {
    if (mEnabled) {
        glDisable(GL_BLEND);
        mEnabled = false;
    }
}

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

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

void Blend::getFactors(SkXfermode::Mode mode, bool swapSrcDst, GLenum* outSrc, GLenum* outDst) {
    *outSrc = swapSrcDst ? kBlendsSwap[mode].src : kBlends[mode].src;
    *outDst = swapSrcDst ? kBlendsSwap[mode].dst : kBlends[mode].dst;
}

void Blend::setFactors(GLenum srcMode, GLenum dstMode) {
    if (srcMode == GL_ZERO && dstMode == GL_ZERO) {
        disable();
    } else {
        if (!mEnabled) {
            glEnable(GL_BLEND);
            mEnabled = true;
        }

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

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