Checking for valid colorType, alphaType, colorSpace in SkCodec

src/codec/SkCodecPriv.h

 /*
  * Copyright 2015 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkCodecPriv_DEFINED
 #define SkCodecPriv_DEFINED
 
@@ skipping 89 matching lines @@
                 break;
             default:
                 // We cannot decode a non-opaque image to opaque (or unknown)
                 return false;
         }
     }
     return true;
 }
 
 /*
+ * Original version of conversion_possible that does not account for color spaces.
+ * Used by codecs that have not been updated to support color spaces.
+ * This is not synonymous with decoding in "legacy mode".  Codecs should be able

[scroggo, 2016/09/08 16:33:11]

I vote we use a different name. Conversion possible ignore color space? (With
underscores) Maybe too lengthy,...

[msarett, 2016/09/08 16:49:45]

Works for me - also removed this part of the comment.

+ * to support decodes in "legacy mode" and in "color correct modes".  Codecs that
+ * still use this function ignore color spaces and always decode in "legacy mode".
+ *
  * Most of our codecs support the same conversions:
  * - opaque to any alpha type
  * - 565 only if opaque
  * - premul to unpremul and vice versa
- * - always support N32
+ * - always support RGBA, BGRA
  * - otherwise match the src color type
  */
-static inline bool conversion_possible(const SkImageInfo& dst, const SkImageInfo& src) {
+static inline bool legacy_conversion_possible(const SkImageInfo& dst, const SkImageInfo& src) {
     // Ensure the alpha type is valid
     if (!valid_alpha(dst.alphaType(), src.alphaType())) {
         return false;
     }
 
     // Check for supported color types
     switch (dst.colorType()) {
         case kRGBA_8888_SkColorType:
         case kBGRA_8888_SkColorType:
             return true;
@@ skipping 200 matching lines @@
     // We never perform a color xform in legacy mode.
     bool isLegacy = nullptr == dstInfo.colorSpace();
 
     return !isLegacy && (needsPremul || isF16 || srcDstNotEqual);
 }
 
 static inline SkAlphaType select_alpha_xform(SkAlphaType dstAlphaType, SkAlphaType srcAlphaType) {
     return (kOpaque_SkAlphaType == srcAlphaType) ? kOpaque_SkAlphaType : dstAlphaType;
 }
 
+/*
+ * Alpha Type Conversions
+ * - kOpaque to kOpaque, kUnpremul, kPremul is valid
+ * - kUnpremul to kUnpremul, kPremul is valid
+ *
+ * Color Type Conversions
+ * - Always support kRGBA_8888, kBGRA_8888
+ * - Support kRGBA_F16 when there is a linear dst color space
+ * - Support kIndex8 if it matches the src
+ * - Support k565, kGray8 if kOpaque and color correction is not required
+ */
+static inline bool conversion_possible(const SkImageInfo& dst, const SkImageInfo& src) {
+    // Ensure the alpha type is valid.
+    if (!valid_alpha(dst.alphaType(), src.alphaType())) {
+        return false;
+    }
+
+    // Check for supported color types.
+    switch (dst.colorType()) {
+        case kRGBA_8888_SkColorType:
+        case kBGRA_8888_SkColorType:
+            return true;
+        case kRGBA_F16_SkColorType:
+            return dst.colorSpace() && dst.colorSpace()->gammaIsLinear();
+        case kIndex_8_SkColorType:
+            return kIndex_8_SkColorType == src.colorType();
+        case kRGB_565_SkColorType:
+        case kGray_8_SkColorType:
+            return kOpaque_SkAlphaType == src.alphaType() && !needs_color_xform(dst, src);
+        default:
+            return false;
+    }
+}
+
 #endif // SkCodecPriv_DEFINED