change pixel-serializer to support reencoding existing data

src/images/SkImageDecoder_ktx.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkColorPriv.h"
 #include "SkImageDecoder.h"
 #include "SkPixelRef.h"
@@ skipping 234 matching lines @@
 // will repurpose the existing ETC1 data into a KTX file. If the data contains
 // KTX data, then we simply return a copy of the same data. For all other files,
 // the underlying KTX library tries to do its best to encode the appropriate
 // data specified by the bitmap based on the config. (i.e. kAlpha8_Config will
 // be represented as a full resolution 8-bit image dump with the appropriate
 // OpenGL defines in the header).
 
 class SkKTXImageEncoder : public SkImageEncoder {
 protected:
     bool onEncode(SkWStream* stream, const SkBitmap& bm, int quality) override;
+    SkData* onReencodeData(SkData*) override;
 
 private:
     virtual bool encodePKM(SkWStream* stream, const SkData *data);
     typedef SkImageEncoder INHERITED;
 };
 
+SkData* SkKTXImageEncoder::onReencodeData(SkData* encoded) {
+    const uint8_t* bytes = encoded->bytes();
+    if (etc1_pkm_is_valid(bytes)) {
+        SkDynamicMemoryWStream stream;
+        if (this->encodePKM(&stream, encoded)) {
+            return stream.copyToData();
+        }
+    }
+    // Is it a KTX file??
+    if (SkKTXFile::is_ktx(bytes)) {
+        return SkRef(encoded);
+    }
+    return nullptr;
+}
+
 bool SkKTXImageEncoder::onEncode(SkWStream* stream, const SkBitmap& bitmap, int) {
     if (!bitmap.pixelRef()) {
         return false;
     }
-    SkAutoDataUnref data(bitmap.pixelRef()->refEncodedData());
 
-    // Is this even encoded data?
-    if (data) {
-        const uint8_t *bytes = data->bytes();
-        if (etc1_pkm_is_valid(bytes)) {
-            return this->encodePKM(stream, data);
+    SkAutoDataUnref encoded(bitmap.pixelRef()->refEncodedData());
+    if (encoded) {
+        SkAutoDataUnref reencoded(this->onReencodeData(encoded));
+        if (reencoded) {
+            return stream->write(reencoded->bytes(), reencoded->size());
         }
-
-        // Is it a KTX file??
-        if (SkKTXFile::is_ktx(bytes)) {
-            return stream->write(bytes, data->size());
-        }
-        
-        // If it's neither a KTX nor a PKM, then we need to
-        // get at the actual pixels, so fall through and decompress...
     }
-
     return SkKTXFile::WriteBitmapToKTX(stream, bitmap);
 }
 
 bool SkKTXImageEncoder::encodePKM(SkWStream* stream, const SkData *data) {
     const uint8_t* bytes = data->bytes();
     SkASSERT(etc1_pkm_is_valid(bytes));
 
     etc1_uint32 width = etc1_pkm_get_width(bytes);
     etc1_uint32 height = etc1_pkm_get_height(bytes);
 
@@ skipping 28 matching lines @@
     return SkImageDecoder::kUnknown_Format;
 }
 
 SkImageEncoder* sk_libktx_efactory(SkImageEncoder::Type t) {
     return (SkImageEncoder::kKTX_Type == t) ? new SkKTXImageEncoder : nullptr;
 }
 
 static SkImageDecoder_DecodeReg gReg(sk_libktx_dfactory);
 static SkImageDecoder_FormatReg gFormatReg(get_format_ktx);
 static SkImageEncoder_EncodeReg gEReg(sk_libktx_efactory);