Revert of Delete SkImageDecoder

src/images/SkImageDecoder_ktx.cpp

Index: src/images/SkImageDecoder_ktx.cpp
diff --git a/src/images/SkImageDecoder_ktx.cpp b/src/images/SkImageDecoder_ktx.cpp
index 79f0293c2a0de42d9842173b46d61c1507657076..156674565c0dff6c91adfed7331a02d16d558797 100644
--- a/src/images/SkImageDecoder_ktx.cpp
+++ b/src/images/SkImageDecoder_ktx.cpp
@@ -6,9 +6,10 @@
  */
 
 #include "SkColorPriv.h"
-#include "SkImageEncoder.h"
+#include "SkImageDecoder.h"
 #include "SkImageGenerator.h"
 #include "SkPixelRef.h"
+#include "SkScaledBitmapSampler.h"
 #include "SkStream.h"
 #include "SkStreamPriv.h"
 #include "SkTypes.h"
@@ -16,13 +17,229 @@
 #include "ktx.h"
 #include "etc1.h"
 
-///////////////////////////////////////////////////////////////////////////////
-
-// KTX Image Encoder
-//
+/////////////////////////////////////////////////////////////////////////////////////////
+
+
+/////////////////////////////////////////////////////////////////////////////////////////
+
+// KTX Image decoder
+// ---
 // KTX is a general texture data storage file format ratified by the Khronos Group. As an
 // overview, a KTX file contains all of the appropriate values needed to fully specify a
 // texture in an OpenGL application, including the use of compressed data.
+//
+// This decoder is meant to be used with an SkDiscardablePixelRef so that GPU backends
+// can sniff the data before creating a texture. If they encounter a compressed format
+// that they understand, they can then upload the data directly to the GPU. Otherwise,
+// they will decode the data into a format that Skia supports.
+
+class SkKTXImageDecoder : public SkImageDecoder {
+public:
+    SkKTXImageDecoder() { }
+
+    Format getFormat() const override {
+        return kKTX_Format;
+    }
+
+protected:
+    Result onDecode(SkStream* stream, SkBitmap* bm, Mode) override;
+
+private:
+    typedef SkImageDecoder INHERITED;
+};
+
+SkImageDecoder::Result SkKTXImageDecoder::onDecode(SkStream* stream, SkBitmap* bm, Mode mode) {
+    // TODO: Implement SkStream::copyToData() that's cheap for memory and file streams
+    auto data = SkCopyStreamToData(stream);
+    if (nullptr == data) {
+        return kFailure;
+    }
+
+    SkKTXFile ktxFile(data.get());
+    if (!ktxFile.valid()) {
+        return kFailure;
+    }
+
+    const unsigned short width = ktxFile.width();
+    const unsigned short height = ktxFile.height();
+
+    // Set a flag if our source is premultiplied alpha
+    const SkString premulKey("KTXPremultipliedAlpha");
+    const bool bSrcIsPremul = ktxFile.getValueForKey(premulKey) == SkString("True");
+
+    // Setup the sampler...
+    SkScaledBitmapSampler sampler(width, height, this->getSampleSize());
+
+    // Determine the alpha of the bitmap...
+    SkAlphaType alphaType = kOpaque_SkAlphaType;
+    if (ktxFile.isRGBA8()) {
+        if (this->getRequireUnpremultipliedColors()) {
+            alphaType = kUnpremul_SkAlphaType;
+            // If the client wants unpremul colors and we only have
+            // premul, then we cannot honor their wish.
+            if (bSrcIsPremul) {
+                return kFailure;
+            }
+        } else {
+            alphaType = kPremul_SkAlphaType;
+        }
+    }
+
+    // Search through the compressed formats to see if the KTX file is holding
+    // compressed data
+    bool ktxIsCompressed = false;
+    SkTextureCompressor::Format ktxCompressedFormat;
+    for (int i = 0; i < SkTextureCompressor::kFormatCnt; ++i) {
+        SkTextureCompressor::Format fmt = static_cast<SkTextureCompressor::Format>(i);
+        if (ktxFile.isCompressedFormat(fmt)) {
+            ktxIsCompressed = true;
+            ktxCompressedFormat = fmt;
+            break;
+        }
+    }
+
+    // If the compressed format is a grayscale image, then setup the bitmap properly...
+    bool isCompressedAlpha = ktxIsCompressed &&
+        ((SkTextureCompressor::kLATC_Format == ktxCompressedFormat) ||
+         (SkTextureCompressor::kR11_EAC_Format == ktxCompressedFormat));
+
+    // Set the image dimensions and underlying pixel type.
+    if (isCompressedAlpha) {
+        const int w = sampler.scaledWidth();
+        const int h = sampler.scaledHeight();
+        bm->setInfo(SkImageInfo::MakeA8(w, h));
+    } else {
+        const int w = sampler.scaledWidth();
+        const int h = sampler.scaledHeight();
+        bm->setInfo(SkImageInfo::MakeN32(w, h, alphaType));
+    }
+    
+    if (SkImageDecoder::kDecodeBounds_Mode == mode) {
+        return kSuccess;
+    }
+
+    // If we've made it this far, then we know how to grok the data.
+    if (!this->allocPixelRef(bm, nullptr)) {
+        return kFailure;
+    }
+
+    // Lock the pixels, since we're about to write to them...
+    SkAutoLockPixels alp(*bm);
+
+    if (isCompressedAlpha) {
+        if (!sampler.begin(bm, SkScaledBitmapSampler::kGray, *this)) {
+            return kFailure;
+        }
+
+        // Alpha data is only a single byte per pixel.
+        int nPixels = width * height;
+        SkAutoMalloc outRGBData(nPixels);
+        uint8_t *outRGBDataPtr = reinterpret_cast<uint8_t *>(outRGBData.get());
+
+        // Decode the compressed format
+        const uint8_t *buf = reinterpret_cast<const uint8_t *>(ktxFile.pixelData());
+        if (!SkTextureCompressor::DecompressBufferFromFormat(
+                outRGBDataPtr, width, buf, width, height, ktxCompressedFormat)) {
+            return kFailure;
+        }
+
+        // Set each of the pixels...
+        const int srcRowBytes = width;
+        const int dstHeight = sampler.scaledHeight();
+        const uint8_t *srcRow = reinterpret_cast<uint8_t *>(outRGBDataPtr);
+        srcRow += sampler.srcY0() * srcRowBytes;
+        for (int y = 0; y < dstHeight; ++y) {
+            sampler.next(srcRow);
+            srcRow += sampler.srcDY() * srcRowBytes;
+        }
+
+        return kSuccess;
+
+    } else if (ktxFile.isCompressedFormat(SkTextureCompressor::kETC1_Format)) {
+        if (!sampler.begin(bm, SkScaledBitmapSampler::kRGB, *this)) {
+            return kFailure;
+        }
+
+        // ETC1 Data is encoded as RGB pixels, so we should extract it as such
+        int nPixels = width * height;
+        SkAutoMalloc outRGBData(nPixels * 3);
+        uint8_t *outRGBDataPtr = reinterpret_cast<uint8_t *>(outRGBData.get());
+
+        // Decode ETC1
+        const uint8_t *buf = reinterpret_cast<const uint8_t *>(ktxFile.pixelData());
+        if (!SkTextureCompressor::DecompressBufferFromFormat(
+                outRGBDataPtr, width*3, buf, width, height, SkTextureCompressor::kETC1_Format)) {
+            return kFailure;
+        }
+
+        // Set each of the pixels...
+        const int srcRowBytes = width * 3;
+        const int dstHeight = sampler.scaledHeight();
+        const uint8_t *srcRow = reinterpret_cast<uint8_t *>(outRGBDataPtr);
+        srcRow += sampler.srcY0() * srcRowBytes;
+        for (int y = 0; y < dstHeight; ++y) {
+            sampler.next(srcRow);
+            srcRow += sampler.srcDY() * srcRowBytes;
+        }
+
+        return kSuccess;
+
+    } else if (ktxFile.isRGB8()) {
+
+        // Uncompressed RGB data (without alpha)
+        if (!sampler.begin(bm, SkScaledBitmapSampler::kRGB, *this)) {
+            return kFailure;
+        }
+
+        // Just need to read RGB pixels
+        const int srcRowBytes = width * 3;
+        const int dstHeight = sampler.scaledHeight();
+        const uint8_t *srcRow = reinterpret_cast<const uint8_t *>(ktxFile.pixelData());
+        srcRow += sampler.srcY0() * srcRowBytes;
+        for (int y = 0; y < dstHeight; ++y) {
+            sampler.next(srcRow);
+            srcRow += sampler.srcDY() * srcRowBytes;
+        }
+
+        return kSuccess;
+
+    } else if (ktxFile.isRGBA8()) {
+
+        // Uncompressed RGBA data
+
+        // If we know that the image contains premultiplied alpha, then
+        // we need to turn off the premultiplier
+        SkScaledBitmapSampler::Options opts (*this);
+        if (bSrcIsPremul) {
+            SkASSERT(bm->alphaType() == kPremul_SkAlphaType);
+            SkASSERT(!this->getRequireUnpremultipliedColors());
+
+            opts.fPremultiplyAlpha = false;
+        } 
+
+        if (!sampler.begin(bm, SkScaledBitmapSampler::kRGBA, opts)) {
+            return kFailure;
+        }
+
+        // Just need to read RGBA pixels
+        const int srcRowBytes = width * 4;
+        const int dstHeight = sampler.scaledHeight();
+        const uint8_t *srcRow = reinterpret_cast<const uint8_t *>(ktxFile.pixelData());
+        srcRow += sampler.srcY0() * srcRowBytes;
+        for (int y = 0; y < dstHeight; ++y) {
+            sampler.next(srcRow);
+            srcRow += sampler.srcDY() * srcRowBytes;
+        }
+
+        return kSuccess;
+    }
+
+    return kFailure;
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+// KTX Image Encoder
 //
 // This encoder takes a best guess at how to encode the bitmap passed to it. If
 // there is an installed discardable pixel ref with existing PKM data, then we
@@ -87,11 +304,28 @@
 }
 
 /////////////////////////////////////////////////////////////////////////////////////////
+DEFINE_DECODER_CREATOR(KTXImageDecoder);
 DEFINE_ENCODER_CREATOR(KTXImageEncoder);
 /////////////////////////////////////////////////////////////////////////////////////////
 
+static SkImageDecoder* sk_libktx_dfactory(SkStreamRewindable* stream) {
+    if (SkKTXFile::is_ktx(stream)) {
+        return new SkKTXImageDecoder;
+    }
+    return nullptr;
+}
+
+static SkImageDecoder::Format get_format_ktx(SkStreamRewindable* stream) {
+    if (SkKTXFile::is_ktx(stream)) {
+        return SkImageDecoder::kKTX_Format;
+    }
+    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);