Blend.cpp revision 44eb2c00861098dd3e2950d923646814b4cc57c2 
1/*
2 * Copyright (C) 2015 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16#include <renderstate/Blend.h>
17#include "Program.h"
18
19#include "ShadowTessellator.h"
20
21namespace android {
22namespace uirenderer {
23
24/**
25 * Structure mapping Skia xfermodes to OpenGL blending factors.
26 */
27struct Blender {
28    SkXfermode::Mode mode;
29    GLenum src;
30    GLenum dst;
31};
32
33// In this array, the index of each Blender equals the value of the first
34// entry. For instance, gBlends[1] == gBlends[SkXfermode::kSrc_Mode]
35const Blender kBlends[] = {
36    { SkXfermode::kClear_Mode,    GL_ZERO,                GL_ONE_MINUS_SRC_ALPHA },
37    { SkXfermode::kSrc_Mode,      GL_ONE,                 GL_ZERO },
38    { SkXfermode::kDst_Mode,      GL_ZERO,                GL_ONE },
39    { SkXfermode::kSrcOver_Mode,  GL_ONE,                 GL_ONE_MINUS_SRC_ALPHA },
40    { SkXfermode::kDstOver_Mode,  GL_ONE_MINUS_DST_ALPHA, GL_ONE },
41    { SkXfermode::kSrcIn_Mode,    GL_DST_ALPHA,           GL_ZERO },
42    { SkXfermode::kDstIn_Mode,    GL_ZERO,                GL_SRC_ALPHA },
43    { SkXfermode::kSrcOut_Mode,   GL_ONE_MINUS_DST_ALPHA, GL_ZERO },
44    { SkXfermode::kDstOut_Mode,   GL_ZERO,                GL_ONE_MINUS_SRC_ALPHA },
45    { SkXfermode::kSrcATop_Mode,  GL_DST_ALPHA,           GL_ONE_MINUS_SRC_ALPHA },
46    { SkXfermode::kDstATop_Mode,  GL_ONE_MINUS_DST_ALPHA, GL_SRC_ALPHA },
47    { SkXfermode::kXor_Mode,      GL_ONE_MINUS_DST_ALPHA, GL_ONE_MINUS_SRC_ALPHA },
48    { SkXfermode::kPlus_Mode,     GL_ONE,                 GL_ONE },
49    { SkXfermode::kModulate_Mode, GL_ZERO,                GL_SRC_COLOR },
50    { SkXfermode::kScreen_Mode,   GL_ONE,                 GL_ONE_MINUS_SRC_COLOR }
51};
52
53// This array contains the swapped version of each SkXfermode. For instance
54// this array's SrcOver blending mode is actually DstOver. You can refer to
55// createLayer() for more information on the purpose of this array.
56const Blender kBlendsSwap[] = {
57    { SkXfermode::kClear_Mode,    GL_ONE_MINUS_DST_ALPHA, GL_ZERO },
58    { SkXfermode::kSrc_Mode,      GL_ZERO,                GL_ONE },
59    { SkXfermode::kDst_Mode,      GL_ONE,                 GL_ZERO },
60    { SkXfermode::kSrcOver_Mode,  GL_ONE_MINUS_DST_ALPHA, GL_ONE },
61    { SkXfermode::kDstOver_Mode,  GL_ONE,                 GL_ONE_MINUS_SRC_ALPHA },
62    { SkXfermode::kSrcIn_Mode,    GL_ZERO,                GL_SRC_ALPHA },
63    { SkXfermode::kDstIn_Mode,    GL_DST_ALPHA,           GL_ZERO },
64    { SkXfermode::kSrcOut_Mode,   GL_ZERO,                GL_ONE_MINUS_SRC_ALPHA },
65    { SkXfermode::kDstOut_Mode,   GL_ONE_MINUS_DST_ALPHA, GL_ZERO },
66    { SkXfermode::kSrcATop_Mode,  GL_ONE_MINUS_DST_ALPHA, GL_SRC_ALPHA },
67    { SkXfermode::kDstATop_Mode,  GL_DST_ALPHA,           GL_ONE_MINUS_SRC_ALPHA },
68    { SkXfermode::kXor_Mode,      GL_ONE_MINUS_DST_ALPHA, GL_ONE_MINUS_SRC_ALPHA },
69    { SkXfermode::kPlus_Mode,     GL_ONE,                 GL_ONE },
70    { SkXfermode::kModulate_Mode, GL_DST_COLOR,           GL_ZERO },
71    { SkXfermode::kScreen_Mode,   GL_ONE_MINUS_DST_COLOR, GL_ONE }
72};
73
74Blend::Blend()
75    : mEnabled(false)
76    , mSrcMode(GL_ZERO)
77    , mDstMode(GL_ZERO) {
78    // gl blending off by default
79}
80
81void Blend::enable(SkXfermode::Mode mode, bool swapSrcDst) {
82    // enable
83    if (!mEnabled) {
84        glEnable(GL_BLEND);
85        mEnabled = true;
86    }
87
88    // select blend mode
89    GLenum sourceMode = swapSrcDst ? kBlendsSwap[mode].src : kBlends[mode].src;
90    GLenum destMode = swapSrcDst ? kBlendsSwap[mode].dst : kBlends[mode].dst;
91
92    if (sourceMode != mSrcMode || destMode != mSrcMode) {
93        glBlendFunc(sourceMode, destMode);
94        mSrcMode = sourceMode;
95        mDstMode = destMode;
96    }
97}
98
99void Blend::disable() {
100    if (mEnabled) {
101        glDisable(GL_BLEND);
102        mEnabled = false;
103    }
104}
105
106void Blend::invalidate() {
107    syncEnabled();
108    mSrcMode = mDstMode = GL_ZERO;
109}
110
111void Blend::syncEnabled() {
112    if (mEnabled) {
113        glEnable(GL_BLEND);
114    } else {
115        glDisable(GL_BLEND);
116    }
117}
118
119} /* namespace uirenderer */
120} /* namespace android */
121
122