add gamma/sRGB to SkImageInfo

src/core/SkImageInfo.cpp

 /*
  * Copyright 2010 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkImageInfo.h"
 #include "SkReadBuffer.h"
 #include "SkWriteBuffer.h"
 
 static bool alpha_type_is_valid(SkAlphaType alphaType) {
     return (alphaType >= 0) && (alphaType <= kLastEnum_SkAlphaType);
 }
 
 static bool color_type_is_valid(SkColorType colorType) {
     return (colorType >= 0) && (colorType <= kLastEnum_SkColorType);
 }
 
+static bool color_type_supports_sRGB(SkColorType colorType) {
+    switch (colorType) {
+        case kRGBA_8888_SkColorType:
+        case kBGRA_8888_SkColorType:
+            return true;
+        default:
+            return false;
+    }
+}
+
+static bool color_type_supports_gamma(SkColorType colorType) {
+    switch (colorType) {
+        case kRGBA_8888_SkColorType:
+        case kBGRA_8888_SkColorType:
+        // case kLuminance ...
+            return true;
+        default:
+            return false;
+    }
+}
+
+static bool pin_gamma_to_legal(float gamma) {
+    if (!SkScalarIsFinite(gamma)) {
+        return 1;
+    }
+    // these limits are just made up -- feel free to change them within reason
+    const float min_gamma = 0.01f;
+    const float max_gamma = 4.0;
+    return SkScalarPin(gamma, min_gamma, max_gamma);
+}
+
+SkImageInfo SkImageInfo::MakeSRGB(int width, int height, SkColorType ct, SkAlphaType at) {
+    Profile p = color_type_supports_sRGB(ct) ? kSRGB_Profile : kUnknown_Profile;
+    return SkImageInfo(width, height, ct, at, p, 0);
+}
+
+SkImageInfo SkImageInfo::MakeWithGamma(int width, int height, SkColorType ct, SkAlphaType at,
+                                       float gamma) {
+    Profile p;
+    if (color_type_supports_gamma(ct)) {
+        gamma = pin_gamma_to_legal(gamma);
+        p = kExponential_Profile;
+    } else {
+        p = kUnknown_Profile;
+        gamma = 0;
+    }
+    return SkImageInfo(width, height, ct, at, p, gamma);
+}
+
 void SkImageInfo::unflatten(SkReadBuffer& buffer) {
     fWidth = buffer.read32();
     fHeight = buffer.read32();
 
     uint32_t packed = buffer.read32();
     SkASSERT(0 == (packed >> 16));
     fAlphaType = (SkAlphaType)((packed >> 8) & 0xFF);
     fColorType = (SkColorType)((packed >> 0) & 0xFF);
     buffer.validate(alpha_type_is_valid(fAlphaType) &&
                     color_type_is_valid(fColorType));
@@ skipping 32 matching lines @@
             alphaType = kOpaque_SkAlphaType;
             break;
         default:
             return false;
     }
     if (canonical) {
         *canonical = alphaType;
     }
     return true;
 }