SkImageInfo.cpp revision 615c369777258231054840a88cdb74c68c382485 
1/*
2 * Copyright 2010 Google Inc.
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 */
7
8#include "SkImageInfo.h"
9#include "SkReadBuffer.h"
10#include "SkWriteBuffer.h"
11
12static bool color_type_supports_sRGB(SkColorType colorType) {
13    switch (colorType) {
14        case kRGBA_8888_SkColorType:
15        case kBGRA_8888_SkColorType:
16            return true;
17        default:
18            return false;
19    }
20}
21
22static bool color_type_supports_gamma(SkColorType colorType) {
23    switch (colorType) {
24        case kRGBA_8888_SkColorType:
25        case kBGRA_8888_SkColorType:
26        // case kLuminance ...
27            return true;
28        default:
29            return false;
30    }
31}
32
33static float pin_gamma_to_legal(float gamma) {
34    if (!SkScalarIsFinite(gamma)) {
35        return 1;
36    }
37    // these limits are just made up -- feel free to change them within reason
38    const float min_gamma = 0.01f;
39    const float max_gamma = 4.0;
40    return SkScalarPin(gamma, min_gamma, max_gamma);
41}
42
43SkImageInfo SkImageInfo::MakeSRGB(int width, int height, SkColorType ct, SkAlphaType at) {
44    Profile p = color_type_supports_sRGB(ct) ? kSRGB_Profile : kUnknown_Profile;
45    return SkImageInfo(width, height, ct, at, p, 0);
46}
47
48SkImageInfo SkImageInfo::MakeWithGamma(int width, int height, SkColorType ct, SkAlphaType at,
49                                       float gamma) {
50    Profile p;
51    if (color_type_supports_gamma(ct)) {
52        gamma = pin_gamma_to_legal(gamma);
53        p = kExponential_Profile;
54    } else {
55        p = kUnknown_Profile;
56        gamma = 0;
57    }
58    return SkImageInfo(width, height, ct, at, p, gamma);
59}
60
61bool SkColorTypeValidateAlphaType(SkColorType colorType, SkAlphaType alphaType,
62                                  SkAlphaType* canonical) {
63    switch (colorType) {
64        case kUnknown_SkColorType:
65            alphaType = kIgnore_SkAlphaType;
66            break;
67        case kAlpha_8_SkColorType:
68            if (kUnpremul_SkAlphaType == alphaType) {
69                alphaType = kPremul_SkAlphaType;
70            }
71            // fall-through
72        case kIndex_8_SkColorType:
73        case kARGB_4444_SkColorType:
74        case kRGBA_8888_SkColorType:
75        case kBGRA_8888_SkColorType:
76            if (kIgnore_SkAlphaType == alphaType) {
77                return false;
78            }
79            break;
80        case kRGB_565_SkColorType:
81            alphaType = kOpaque_SkAlphaType;
82            break;
83        default:
84            return false;
85    }
86    if (canonical) {
87        *canonical = alphaType;
88    }
89    return true;
90}
91
92void SkImageInfo::unflatten(SkReadBuffer& buffer) {
93    *this = Unflatten(buffer);
94}
95
96////////////////////////////////////////////////////////////////////////////////////////////
97
98static bool alpha_type_is_valid(SkAlphaType alphaType) {
99    return (alphaType >= 0) && (alphaType <= kLastEnum_SkAlphaType);
100}
101
102static bool color_type_is_valid(SkColorType colorType) {
103    return (colorType >= 0) && (colorType <= kLastEnum_SkColorType);
104}
105
106static float igamma_to_gamma(int gamma3dot9) {
107    return gamma3dot9 / 512.0f;
108}
109
110static unsigned gamma_to_igamma(float gamma) {
111    SkASSERT(gamma >= 0 && gamma < 8);
112    int igamma = SkScalarRoundToInt(gamma * 512);
113    SkASSERT(igamma >= 0 && igamma <= 0xFFF);
114    return igamma;
115}
116
117SkImageInfo SkImageInfo::Unflatten(SkReadBuffer& buffer) {
118    int width = buffer.read32();
119    int height = buffer.read32();
120    uint32_t packed = buffer.read32();
121
122    SkColorType ct = (SkColorType)((packed >> 0) & 0xFF);   // 8 bits for colortype
123    SkAlphaType at = (SkAlphaType)((packed >> 8) & 0xFF);   // 8 bits for alphatype
124    if (!alpha_type_is_valid(at) || !color_type_is_valid(ct)) {
125        return MakeUnknown();
126    }
127
128    // Earlier formats always stored 0 in the upper 16 bits. That corresponds to
129    // days before we had gamma/profile. That happens to correspond to kUnknown_Profile,
130    // which means we can just ignore the gamma value anyways.
131    //
132    int iprofile = ((packed >> 16) & 0xF);  // 4 bits for profile
133
134    switch (iprofile) {
135        case kUnknown_Profile:
136            return Make(width, height, ct, at);
137        case kSRGB_Profile:
138            return MakeSRGB(width, height, ct, at);
139        case kExponential_Profile: {
140            int igamma = packed >> 20;      // 12 bits for gamma 3.9
141            float gamma = igamma_to_gamma(igamma);
142            return MakeWithGamma(width, height, ct, at, gamma);
143        }
144        default:
145            (void)buffer.validate(false);
146            return MakeUnknown();
147    }
148}
149
150void SkImageInfo::flatten(SkWriteBuffer& buffer) const {
151    buffer.write32(fWidth);
152    buffer.write32(fHeight);
153
154    SkASSERT(0 == (fColorType & ~0xFF));    // 8 bits for colortype
155    SkASSERT(0 == (fAlphaType & ~0xFF));    // 8 bits for alphatype
156    SkASSERT(0 == (fProfile & ~0xF));       // 4 bits for profile
157    int igamma = gamma_to_igamma(fGamma);   // 12 bits for gamma (if needed)
158
159    uint32_t packed = (igamma << 20) | (fProfile << 16) | (fAlphaType << 8) | fColorType;
160    buffer.write32(packed);
161}
162