Blend.cpp revision 216048ffb0a4c41836c6ddb63f9b2e7a64593837 
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// assumptions made by lookup tables in either this file or ProgramCache
34static_assert(0 == SkXfermode::kClear_Mode, "SkXfermode enums have changed");
35static_assert(1 == SkXfermode::kSrc_Mode, "SkXfermode enums have changed");
36static_assert(2 == SkXfermode::kDst_Mode, "SkXfermode enums have changed");
37static_assert(3 == SkXfermode::kSrcOver_Mode, "SkXfermode enums have changed");
38static_assert(4 == SkXfermode::kDstOver_Mode, "SkXfermode enums have changed");
39static_assert(5 == SkXfermode::kSrcIn_Mode, "SkXfermode enums have changed");
40static_assert(6 == SkXfermode::kDstIn_Mode, "SkXfermode enums have changed");
41static_assert(7 == SkXfermode::kSrcOut_Mode, "SkXfermode enums have changed");
42static_assert(8 == SkXfermode::kDstOut_Mode, "SkXfermode enums have changed");
43static_assert(9 == SkXfermode::kSrcATop_Mode, "SkXfermode enums have changed");
44static_assert(10 == SkXfermode::kDstATop_Mode, "SkXfermode enums have changed");
45static_assert(11 == SkXfermode::kXor_Mode, "SkXfermode enums have changed");
46static_assert(12 == SkXfermode::kPlus_Mode, "SkXfermode enums have changed");
47static_assert(13 == SkXfermode::kModulate_Mode, "SkXfermode enums have changed");
48static_assert(14 == SkXfermode::kScreen_Mode, "SkXfermode enums have changed");
49static_assert(15 == SkXfermode::kOverlay_Mode, "SkXfermode enums have changed");
50static_assert(16 == SkXfermode::kDarken_Mode, "SkXfermode enums have changed");
51static_assert(17 == SkXfermode::kLighten_Mode, "SkXfermode enums have changed");
52
53// In this array, the index of each Blender equals the value of the first
54// entry. For instance, gBlends[1] == gBlends[SkXfermode::kSrc_Mode]
55const Blender kBlends[] = {
56    { SkXfermode::kClear_Mode,    GL_ZERO,                GL_ONE_MINUS_SRC_ALPHA },
57    { SkXfermode::kSrc_Mode,      GL_ONE,                 GL_ZERO },
58    { SkXfermode::kDst_Mode,      GL_ZERO,                GL_ONE },
59    { SkXfermode::kSrcOver_Mode,  GL_ONE,                 GL_ONE_MINUS_SRC_ALPHA },
60    { SkXfermode::kDstOver_Mode,  GL_ONE_MINUS_DST_ALPHA, GL_ONE },
61    { SkXfermode::kSrcIn_Mode,    GL_DST_ALPHA,           GL_ZERO },
62    { SkXfermode::kDstIn_Mode,    GL_ZERO,                GL_SRC_ALPHA },
63    { SkXfermode::kSrcOut_Mode,   GL_ONE_MINUS_DST_ALPHA, GL_ZERO },
64    { SkXfermode::kDstOut_Mode,   GL_ZERO,                GL_ONE_MINUS_SRC_ALPHA },
65    { SkXfermode::kSrcATop_Mode,  GL_DST_ALPHA,           GL_ONE_MINUS_SRC_ALPHA },
66    { SkXfermode::kDstATop_Mode,  GL_ONE_MINUS_DST_ALPHA, GL_SRC_ALPHA },
67    { SkXfermode::kXor_Mode,      GL_ONE_MINUS_DST_ALPHA, GL_ONE_MINUS_SRC_ALPHA },
68    { SkXfermode::kPlus_Mode,     GL_ONE,                 GL_ONE },
69    { SkXfermode::kModulate_Mode, GL_ZERO,                GL_SRC_COLOR },
70    { SkXfermode::kScreen_Mode,   GL_ONE,                 GL_ONE_MINUS_SRC_COLOR }
71};
72
73// This array contains the swapped version of each SkXfermode. For instance
74// this array's SrcOver blending mode is actually DstOver. You can refer to
75// createLayer() for more information on the purpose of this array.
76const Blender kBlendsSwap[] = {
77    { SkXfermode::kClear_Mode,    GL_ONE_MINUS_DST_ALPHA, GL_ZERO },
78    { SkXfermode::kSrc_Mode,      GL_ZERO,                GL_ONE },
79    { SkXfermode::kDst_Mode,      GL_ONE,                 GL_ZERO },
80    { SkXfermode::kSrcOver_Mode,  GL_ONE_MINUS_DST_ALPHA, GL_ONE },
81    { SkXfermode::kDstOver_Mode,  GL_ONE,                 GL_ONE_MINUS_SRC_ALPHA },
82    { SkXfermode::kSrcIn_Mode,    GL_ZERO,                GL_SRC_ALPHA },
83    { SkXfermode::kDstIn_Mode,    GL_DST_ALPHA,           GL_ZERO },
84    { SkXfermode::kSrcOut_Mode,   GL_ZERO,                GL_ONE_MINUS_SRC_ALPHA },
85    { SkXfermode::kDstOut_Mode,   GL_ONE_MINUS_DST_ALPHA, GL_ZERO },
86    { SkXfermode::kSrcATop_Mode,  GL_ONE_MINUS_DST_ALPHA, GL_SRC_ALPHA },
87    { SkXfermode::kDstATop_Mode,  GL_DST_ALPHA,           GL_ONE_MINUS_SRC_ALPHA },
88    { SkXfermode::kXor_Mode,      GL_ONE_MINUS_DST_ALPHA, GL_ONE_MINUS_SRC_ALPHA },
89    { SkXfermode::kPlus_Mode,     GL_ONE,                 GL_ONE },
90    { SkXfermode::kModulate_Mode, GL_DST_COLOR,           GL_ZERO },
91    { SkXfermode::kScreen_Mode,   GL_ONE_MINUS_DST_COLOR, GL_ONE }
92};
93
94Blend::Blend()
95    : mEnabled(false)
96    , mSrcMode(GL_ZERO)
97    , mDstMode(GL_ZERO) {
98    // gl blending off by default
99}
100
101void Blend::enable(SkXfermode::Mode mode, ModeOrderSwap modeUsage) {
102    GLenum srcMode;
103    GLenum dstMode;
104    getFactors(mode, modeUsage, &srcMode, &dstMode);
105    setFactors(srcMode, dstMode);
106}
107
108void Blend::disable() {
109    if (mEnabled) {
110        glDisable(GL_BLEND);
111        mEnabled = false;
112    }
113}
114
115void Blend::invalidate() {
116    syncEnabled();
117    mSrcMode = mDstMode = GL_ZERO;
118}
119
120void Blend::syncEnabled() {
121    if (mEnabled) {
122        glEnable(GL_BLEND);
123    } else {
124        glDisable(GL_BLEND);
125    }
126}
127
128void Blend::getFactors(SkXfermode::Mode mode, ModeOrderSwap modeUsage, GLenum* outSrc, GLenum* outDst) {
129    *outSrc = (modeUsage == ModeOrderSwap::Swap) ? kBlendsSwap[mode].src : kBlends[mode].src;
130    *outDst = (modeUsage == ModeOrderSwap::Swap) ? kBlendsSwap[mode].dst : kBlends[mode].dst;
131}
132
133void Blend::setFactors(GLenum srcMode, GLenum dstMode) {
134    if (srcMode == GL_ZERO && dstMode == GL_ZERO) {
135        disable();
136    } else {
137        if (!mEnabled) {
138            glEnable(GL_BLEND);
139            mEnabled = true;
140        }
141
142        if (srcMode != mSrcMode || dstMode != mDstMode) {
143            glBlendFunc(srcMode, dstMode);
144            mSrcMode = srcMode;
145            mDstMode = dstMode;
146        }
147    }
148}
149
150void Blend::dump() {
151    ALOGD("Blend: enabled %d, func src %d, dst %d", mEnabled, mSrcMode, mDstMode);
152}
153
154} /* namespace uirenderer */
155} /* namespace android */
156
157