Support more swizzles to 565 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 35 matching lines @@
                 break;
             default:
                 // We cannot decode a non-opaque image to opaque (or unknown)
                 return false;
         }
     }
     return true;
 }
 
 /*
+ * Most of our codecs support the same conversions:
+ * - profileType must be the same
+ * - opaque only to opaque (and 565 only if opaque)
+ * - premul to unpremul and vice versa
+ * - always support N32
+ * - otherwise match the src color type
+ */
+static bool conversion_possible(const SkImageInfo& dst, const SkImageInfo& src) {
+    if (dst.profileType() != src.profileType()) {
+        return false;
+    }
+
+    // Ensure the alpha type is valid
+    if (!valid_alpha(dst.alphaType(), src.alphaType())) {
+        return false;
+    }
+
+    // Check for supported color types
+    switch (dst.colorType()) {
+        case kN32_SkColorType:
+            return true;
+        case kRGB_565_SkColorType:
+            return src.alphaType() == kOpaque_SkAlphaType;
+        default:
+            return dst.colorType() == src.colorType();
+    }
+}
+
+/*
  * If there is a color table, get a pointer to the colors, otherwise return NULL
  */
 static const SkPMColor* get_color_ptr(SkColorTable* colorTable) {
      return NULL != colorTable ? colorTable->readColors() : NULL;
 }
 
 /*
  *
  * Copy the codec color table back to the client when kIndex8 color type is requested
  */
@@ skipping 72 matching lines @@
 #endif
 }
 
 #ifdef SK_PRINT_CODEC_MESSAGES
     #define SkCodecPrintf SkDebugf
 #else
     #define SkCodecPrintf(...)
 #endif
 
 #endif // SkCodecPriv_DEFINED