Initial KTX file decoder

src/utils/SkKTXFile.h

+
+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+
+#ifndef SkKTXFile_DEFINED
+#define SkKTXFile_DEFINED
+
+#include "SkTypes.h"
+#include "SkTDArray.h"
+#include "SkString.h"
+
+class SkStreamRewindable;
+
+// KTX Image File
+// ---
+// 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.
+//
+// A full format specification can be found here:
+// http://www.khronos.org/opengles/sdk/tools/KTX/file_format_spec/
+
+class SkKTXFile {
+public:
+    // The ownership of the data remains with the caller. This class is intended
+    // to be used as a logical wrapper around the data in order to properly
+    // access the pixels.

[hal.canary, 2014/06/03 15:41:58]

Alternatively, you could take and ref an SkData here.  Will the normal use case
always have a SkData availible?

[krajcevski, 2014/06/03 18:56:29]

Hrm, this is a good suggestion. It gets rid of my worries that the underlying
data will get freed while this object still lives.

Done.

+    SkKTXFile(const uint8_t* data, size_t dataLen)
+        : fSwapBytes(false)
+    {
+        fValid = this->readKTXFile(data, dataLen);
+    }
+
+    bool valid() const { return fValid; }
+
+    int width() const { return static_cast<int>(fHeader.fPixelWidth); }
+    int height() const { return static_cast<int>(fHeader.fPixelHeight); }
+
+    const uint8_t *pixelData(int mipmap = 0) const {
+        SkASSERT(!this->valid() || mipmap < fPixelData.count());
+        return this->valid() ? fPixelData[mipmap].data() : NULL;
+    }
+
+    int numMipmaps() const { return static_cast<int>(fHeader.fNumberOfMipmapLevels); }
+
+    bool isETC1() const;
+    bool isRGBA8() const;
+    bool isRGB8() const;
+
+    static bool is_ktx(const uint8_t *data);
+    static bool is_ktx(SkStreamRewindable* stream);
+
+private:
+
+    // This header captures all of the data that describes the format
+    // of the image data in a KTX file.
+    struct Header {
+        uint32_t fGLType;
+        uint32_t fGLTypeSize;
+        uint32_t fGLFormat;
+        uint32_t fGLInternalFormat;
+        uint32_t fGLBaseInternalFormat;
+        uint32_t fPixelWidth;
+        uint32_t fPixelHeight;
+        uint32_t fPixelDepth;
+        uint32_t fNumberOfArrayElements;
+        uint32_t fNumberOfFaces;
+        uint32_t fNumberOfMipmapLevels;
+        uint32_t fBytesOfKeyValueData;
+
+        Header() { memset(this, 0, sizeof(*this)); }
+        void swapBytes();
+    } fHeader;
+
+    // A Key Value pair stored in the KTX file. There may be
+    // arbitrarily many of these.
+    class KeyValue {
+    public:
+        KeyValue(size_t size) : fDataSz(size) { }
+        bool readKeyAndValue(const uint8_t *data);
+    
+    private:
+        const size_t fDataSz;
+        SkString fKey;
+        SkString fValue;
+    };
+
+    // The pixel data for a single mipmap level in an image. Based on how
+    // the rest of the data is stored, this may be compressed, a cubemap, etc.
+    // The header will describe the format of this data.
+    class PixelData {
+    public:
+        PixelData(const uint8_t *ptr, size_t sz) : fDataSz(sz), fDataPtr(ptr) { }
+        const uint8_t *data() const { return fDataPtr; }
+        size_t dataSize() const { return fDataSz; }
+    private:
+        const size_t fDataSz;
+        const uint8_t *fDataPtr;
+    };
+
+    bool readKTXFile(const uint8_t *data, size_t dataLen);
+
+    SkTDArray<KeyValue> fKeyValuePairs;
+    SkTDArray<PixelData> fPixelData;
+    bool fValid;
+
+    // If the endianness of the platform is different than the file,
+    // then we need to do proper byte swapping.
+    bool fSwapBytes;
+
+    // Read an integer from a buffer, advance the buffer, and swap
+    // bytes if fSwapBytes is set
+    uint32_t readInt(const uint8_t** buf, size_t* bytesLeft) const;
+};
+
+#endif  // SkKTXFile_DEFINED