Add gamma/sRGB tag to SkImageInfo

src/core/SkImageInfo.cpp

Index: src/core/SkImageInfo.cpp
diff --git a/src/core/SkImageInfo.cpp b/src/core/SkImageInfo.cpp
index e61cd7d45f398c115f36d4332744f65d95e2fdad..44fd808dc85a28c533bfd0a339face99262c3784 100644
--- a/src/core/SkImageInfo.cpp
+++ b/src/core/SkImageInfo.cpp
@@ -9,34 +9,53 @@
 #include "SkReadBuffer.h"
 #include "SkWriteBuffer.h"
 
-static bool alpha_type_is_valid(SkAlphaType alphaType) {
-    return (alphaType >= 0) && (alphaType <= kLastEnum_SkAlphaType);
+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_is_valid(SkColorType colorType) {
-    return (colorType >= 0) && (colorType <= kLastEnum_SkColorType);
+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;
+    }
 }
 
-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));
+static float 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);
 }
 
-void SkImageInfo::flatten(SkWriteBuffer& buffer) const {
-    buffer.write32(fWidth);
-    buffer.write32(fHeight);
+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);
+}
 
-    SkASSERT(0 == (fAlphaType & ~0xFF));
-    SkASSERT(0 == (fColorType & ~0xFF));
-    uint32_t packed = (fAlphaType << 8) | fColorType;
-    buffer.write32(packed);
+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);
 }
 
 bool SkColorTypeValidateAlphaType(SkColorType colorType, SkAlphaType alphaType,
@@ -69,3 +88,74 @@ bool SkColorTypeValidateAlphaType(SkColorType colorType, SkAlphaType alphaType,
     }
     return true;
 }
+
+void SkImageInfo::unflatten(SkReadBuffer& buffer) {
+    *this = Unflatten(buffer);
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////
+
+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 float igamma_to_gamma(int gamma3dot9) {
+    return gamma3dot9 / 512.0f;
+}
+
+static unsigned gamma_to_igamma(float gamma) {
+    SkASSERT(gamma >= 0 && gamma < 8);
+    int igamma = SkScalarRoundToInt(gamma * 512);
+    SkASSERT(igamma >= 0 && igamma <= 0xFFF);
+    return igamma;
+}
+
+SkImageInfo SkImageInfo::Unflatten(SkReadBuffer& buffer) {
+    int width = buffer.read32();
+    int height = buffer.read32();
+    uint32_t packed = buffer.read32();
+    
+    SkColorType ct = (SkColorType)((packed >> 0) & 0xFF);   // 8 bits for colortype
+    SkAlphaType at = (SkAlphaType)((packed >> 8) & 0xFF);   // 8 bits for alphatype
+    if (!alpha_type_is_valid(at) || !color_type_is_valid(ct)) {
+        return MakeUnknown();
+    }
+
+    // Earlier formats always stored 0 in the upper 16 bits. That corresponds to
+    // days before we had gamma/profile. That happens to correspond to kUnknown_Profile,
+    // which means we can just ignore the gamma value anyways.
+    //
+    int iprofile = ((packed >> 16) & 0xF);  // 4 bits for profile
+    
+    switch (iprofile) {
+        case kUnknown_Profile:
+            return Make(width, height, ct, at);
+        case kSRGB_Profile:
+            return MakeSRGB(width, height, ct, at);
+        case kExponential_Profile: {
+            int igamma = packed >> 20;      // 12 bits for gamma 3.9
+            float gamma = igamma_to_gamma(igamma);
+            return MakeWithGamma(width, height, ct, at, gamma);
+        }
+        default:
+            (void)buffer.validate(false);
+            return MakeUnknown();
+    }
+}
+
+void SkImageInfo::flatten(SkWriteBuffer& buffer) const {
+    buffer.write32(fWidth);
+    buffer.write32(fHeight);
+    
+    SkASSERT(0 == (fColorType & ~0xFF));    // 8 bits for colortype
+    SkASSERT(0 == (fAlphaType & ~0xFF));    // 8 bits for alphatype
+    SkASSERT(0 == (fProfile & ~0xF));       // 4 bits for profile
+    int igamma = gamma_to_igamma(fGamma);   // 12 bits for gamma (if needed)
+ 
+    uint32_t packed = (igamma << 20) | (fProfile << 16) | (fAlphaType << 8) | fColorType;
+    buffer.write32(packed);
+}