Simple PKM image decoder.

src/images/SkImageDecoder_pkm.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 "SkStream.h"
+#include "SkStreamHelpers.h"
+#include "SkTypes.h"
+
+#include "etc1.h"
+
+class SkPKMImageDecoder : public SkImageDecoder {
+public:
+    SkPKMImageDecoder() { }
+
+    virtual Format getFormat() const SK_OVERRIDE {
+        return kPKM_Format;
+    }
+
+protected:
+    virtual bool onDecode(SkStream* stream, SkBitmap* bm, Mode) SK_OVERRIDE;
+
+private:
+    typedef SkImageDecoder INHERITED;
+};
+
+/////////////////////////////////////////////////////////////////////////////////////////
+
+bool SkPKMImageDecoder::onDecode(SkStream* stream, SkBitmap* bm, Mode mode)
+{
+    SkAutoMalloc autoMal;
+    const size_t length = CopyStreamToStorage(&autoMal, stream);
+    if (0 == length) {
+        return false;
+    }
+
+    unsigned char* buf = (unsigned char*)autoMal.get();
+    
+    // Make sure original PKM header is there...
+    SkASSERT(etc1_pkm_is_valid(buf));
+
+    const unsigned short width = etc1_pkm_get_width(buf);
+    const unsigned short height = etc1_pkm_get_height(buf);
+
+    // should we allow the Chooser (if present) to pick a config for us???
+    if (!this->chooseFromOneChoice(SkBitmap::kARGB_8888_Config, width, height)) {
+        return false;
+    }
+    
+    bm->setConfig(SkBitmap::kARGB_8888_Config, width, height, 0, kOpaque_SkAlphaType);
+    if (SkImageDecoder::kDecodeBounds_Mode == mode) {
+        return true;
+    }
+    
+    if (!this->allocPixelRef(bm, NULL)) {
+        return false;
+    }
+    
+    // Lock the pixels, since we're about to write to them...
+    SkAutoLockPixels alp(*bm);
+    
+    // Advance buffer past the header
+    buf += ETC_PKM_HEADER_SIZE;
+    
+    // ETC1 Data is encoded as RGB pixels, so we should extract it as such
+    int nPixels = width * height;
+    SkAutoMalloc outRGBData(nPixels * 3);
+    etc1_byte *outRGBDataPtr = reinterpret_cast<etc1_byte *>(outRGBData.get());
+    
+    // Decode ETC1
+    if (etc1_decode_image(buf, outRGBDataPtr, width, height, 3, width*3)) {
+        return false;
+    }
+
+    // Set each of the pixels...
+    const uint8_t *src = reinterpret_cast<uint8_t *>(outRGBDataPtr);
+    uint8_t *dst = reinterpret_cast<uint8_t *>(bm->getPixels());
+    for (int i = 0; i < width*height; ++i) {
+        *dst++ = src[2]; // B
+        *dst++ = src[1]; // G
+        *dst++ = src[0]; // R
+        *dst++ = 0xFF; // Opaque alpha...
+        src += 3;
+    }
+    
+    return true;
+}
+
+/////////////////////////////////////////////////////////////////////////////////////////
+DEFINE_DECODER_CREATOR(PKMImageDecoder);
+/////////////////////////////////////////////////////////////////////////////////////////
+
+static bool is_pkm(SkStreamRewindable* stream) {
+    // Read the PKM header and make sure it's valid.
+    unsigned char buf[ETC_PKM_HEADER_SIZE];
+    if (stream->read((void*)buf, ETC_PKM_HEADER_SIZE) != ETC_PKM_HEADER_SIZE) {
+        return false;
+    }
+
+    return etc1_pkm_is_valid(buf);
+}
+
+static SkImageDecoder* sk_libpkm_dfactory(SkStreamRewindable* stream) {
+    if (is_pkm(stream)) {
+        return SkNEW(SkPKMImageDecoder);
+    }
+    return NULL;
+}
+
+static SkImageDecoder_DecodeReg gReg(sk_libpkm_dfactory);
+
+static SkImageDecoder::Format get_format_pkm(SkStreamRewindable* stream) {
+    if (is_pkm(stream)) {
+        return SkImageDecoder::kPKM_Format;
+    }
+    return SkImageDecoder::kUnknown_Format;
+}
+
+static SkImageDecoder_FormatReg gFormatReg(get_format_pkm);