src/images/SkMovie_gif.cpp - platform/external/skia - Gitiles


 /*
  * Copyright 2006 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.
  */


 #include "SkMovie.h"
 #include "SkColor.h"
 #include "SkColorPriv.h"
 #include "SkStream.h"
 #include "SkTemplates.h"
 #include "SkUtils.h"

 #include "gif_lib.h"

 class SkGIFMovie : public SkMovie {
 public:
     SkGIFMovie(SkStream* stream);
     virtual ~SkGIFMovie();

 protected:
     virtual bool onGetInfo(Info*);
     virtual bool onSetTime(SkMSec);
     virtual bool onGetBitmap(SkBitmap*);

 private:
     GifFileType* fGIF;
     int fCurrIndex;
     int fLastDrawIndex;
     SkBitmap fBackup;
 };

 static int Decode(GifFileType* fileType, GifByteType* out, int size) {
     SkStream* stream = (SkStream*) fileType->UserData;
     return (int) stream->read(out, size);
 }

 SkGIFMovie::SkGIFMovie(SkStream* stream)
 {
     fGIF = DGifOpen( stream, Decode );
     if (NULL == fGIF)
         return;

     if (DGifSlurp(fGIF) != GIF_OK)
     {
         DGifCloseFile(fGIF);
         fGIF = NULL;
     }
     fCurrIndex = -1;
     fLastDrawIndex = -1;
 }

 SkGIFMovie::~SkGIFMovie()
 {
     if (fGIF)
         DGifCloseFile(fGIF);
 }

 static SkMSec savedimage_duration(const SavedImage* image)
 {
     for (int j = 0; j < image->ExtensionBlockCount; j++)
     {
         if (image->ExtensionBlocks[j].Function == GRAPHICS_EXT_FUNC_CODE)
         {
             int size = image->ExtensionBlocks[j].ByteCount;
             SkASSERT(size >= 4);
             const uint8_t* b = (const uint8_t*)image->ExtensionBlocks[j].Bytes;
             return ((b[2] << 8) | b[1]) * 10;
         }
     }
     return 0;
 }

 bool SkGIFMovie::onGetInfo(Info* info)
 {
     if (NULL == fGIF)
         return false;

     SkMSec dur = 0;
     for (int i = 0; i < fGIF->ImageCount; i++)
         dur += savedimage_duration(&fGIF->SavedImages[i]);

     info->fDuration = dur;
     info->fWidth = fGIF->SWidth;
     info->fHeight = fGIF->SHeight;
     info->fIsOpaque = false;    // how to compute?
     return true;
 }

 bool SkGIFMovie::onSetTime(SkMSec time)
 {
     if (NULL == fGIF)
         return false;

     SkMSec dur = 0;
     for (int i = 0; i < fGIF->ImageCount; i++)
     {
         dur += savedimage_duration(&fGIF->SavedImages[i]);
         if (dur >= time)
         {
             fCurrIndex = i;
             return fLastDrawIndex != fCurrIndex;
         }
     }
     fCurrIndex = fGIF->ImageCount - 1;
     return true;
 }

 static void copyLine(uint32_t* dst, const unsigned char* src, const ColorMapObject* cmap,
                      int transparent, int width)
 {
     for (; width > 0; width--, src++, dst++) {
         if (*src != transparent) {
             const GifColorType& col = cmap->Colors[*src];
             *dst = SkPackARGB32(0xFF, col.Red, col.Green, col.Blue);
         }
     }
 }

 static void copyInterlaceGroup(SkBitmap* bm, const unsigned char*& src,
                                const ColorMapObject* cmap, int transparent, int copyWidth,
                                int copyHeight, const GifImageDesc& imageDesc, int rowStep,
                                int startRow)
 {
     int row;
     // every 'rowStep'th row, starting with row 'startRow'
     for (row = startRow; row < copyHeight; row += rowStep) {
         uint32_t* dst = bm->getAddr32(imageDesc.Left, imageDesc.Top + row);
         copyLine(dst, src, cmap, transparent, copyWidth);
         src += imageDesc.Width;
     }

     // pad for rest height
     src += imageDesc.Width * ((imageDesc.Height - row + rowStep - 1) / rowStep);
 }

 static void blitInterlace(SkBitmap* bm, const SavedImage* frame, const ColorMapObject* cmap,
                           int transparent)
 {
     int width = bm->width();
     int height = bm->height();
     GifWord copyWidth = frame->ImageDesc.Width;
     if (frame->ImageDesc.Left + copyWidth > width) {
         copyWidth = width - frame->ImageDesc.Left;
     }

     GifWord copyHeight = frame->ImageDesc.Height;
     if (frame->ImageDesc.Top + copyHeight > height) {
         copyHeight = height - frame->ImageDesc.Top;
     }

     // deinterlace
     const unsigned char* src = (unsigned char*)frame->RasterBits;

     // group 1 - every 8th row, starting with row 0
     copyInterlaceGroup(bm, src, cmap, transparent, copyWidth, copyHeight, frame->ImageDesc, 8, 0);

     // group 2 - every 8th row, starting with row 4
     copyInterlaceGroup(bm, src, cmap, transparent, copyWidth, copyHeight, frame->ImageDesc, 8, 4);

     // group 3 - every 4th row, starting with row 2
     copyInterlaceGroup(bm, src, cmap, transparent, copyWidth, copyHeight, frame->ImageDesc, 4, 2);

     copyInterlaceGroup(bm, src, cmap, transparent, copyWidth, copyHeight, frame->ImageDesc, 2, 1);
 }

 static void blitNormal(SkBitmap* bm, const SavedImage* frame, const ColorMapObject* cmap,
                        int transparent)
 {
     int width = bm->width();
     int height = bm->height();
     const unsigned char* src = (unsigned char*)frame->RasterBits;
     uint32_t* dst = bm->getAddr32(frame->ImageDesc.Left, frame->ImageDesc.Top);
     GifWord copyWidth = frame->ImageDesc.Width;
     if (frame->ImageDesc.Left + copyWidth > width) {
         copyWidth = width - frame->ImageDesc.Left;
     }

     GifWord copyHeight = frame->ImageDesc.Height;
     if (frame->ImageDesc.Top + copyHeight > height) {
         copyHeight = height - frame->ImageDesc.Top;
     }

     int srcPad, dstPad;
     dstPad = width - copyWidth;
     srcPad = frame->ImageDesc.Width - copyWidth;
     for (; copyHeight > 0; copyHeight--) {
         copyLine(dst, src, cmap, transparent, copyWidth);
         src += frame->ImageDesc.Width;
         dst += width;
     }
 }

 static void fillRect(SkBitmap* bm, GifWord left, GifWord top, GifWord width, GifWord height,
                      uint32_t col)
 {
     int bmWidth = bm->width();
     int bmHeight = bm->height();
     uint32_t* dst = bm->getAddr32(left, top);
     GifWord copyWidth = width;
     if (left + copyWidth > bmWidth) {
         copyWidth = bmWidth - left;
     }

     GifWord copyHeight = height;
     if (top + copyHeight > bmHeight) {
         copyHeight = bmHeight - top;
     }

     for (; copyHeight > 0; copyHeight--) {
         sk_memset32(dst, col, copyWidth);
         dst += bmWidth;
     }
 }

 static void drawFrame(SkBitmap* bm, const SavedImage* frame, const ColorMapObject* cmap)
 {
     int transparent = -1;

     for (int i = 0; i < frame->ExtensionBlockCount; ++i) {
         ExtensionBlock* eb = frame->ExtensionBlocks + i;
         if (eb->Function == GRAPHICS_EXT_FUNC_CODE &&
             eb->ByteCount == 4) {
             bool has_transparency = ((eb->Bytes[0] & 1) == 1);
             if (has_transparency) {
                 transparent = (unsigned char)eb->Bytes[3];
             }
         }
     }

     if (frame->ImageDesc.ColorMap != NULL) {
         // use local color table
         cmap = frame->ImageDesc.ColorMap;
     }

     if (cmap == NULL || cmap->ColorCount != (1 << cmap->BitsPerPixel)) {
         SkDEBUGFAIL("bad colortable setup");
         return;
     }

     if (frame->ImageDesc.Interlace) {
         blitInterlace(bm, frame, cmap, transparent);
     } else {
         blitNormal(bm, frame, cmap, transparent);
     }
 }

 static bool checkIfWillBeCleared(const SavedImage* frame)
 {
     for (int i = 0; i < frame->ExtensionBlockCount; ++i) {
         ExtensionBlock* eb = frame->ExtensionBlocks + i;
         if (eb->Function == GRAPHICS_EXT_FUNC_CODE &&
             eb->ByteCount == 4) {
             // check disposal method
             int disposal = ((eb->Bytes[0] >> 2) & 7);
             if (disposal == 2 || disposal == 3) {
                 return true;
             }
         }
     }
     return false;
 }

 static void getTransparencyAndDisposalMethod(const SavedImage* frame, bool* trans, int* disposal)
 {
     *trans = false;
     *disposal = 0;
     for (int i = 0; i < frame->ExtensionBlockCount; ++i) {
         ExtensionBlock* eb = frame->ExtensionBlocks + i;
         if (eb->Function == GRAPHICS_EXT_FUNC_CODE &&
             eb->ByteCount == 4) {
             *trans = ((eb->Bytes[0] & 1) == 1);
             *disposal = ((eb->Bytes[0] >> 2) & 7);
         }
     }
 }

 // return true if area of 'target' is completely covers area of 'covered'
 static bool checkIfCover(const SavedImage* target, const SavedImage* covered)
 {
     if (target->ImageDesc.Left <= covered->ImageDesc.Left
         && covered->ImageDesc.Left + covered->ImageDesc.Width <=
                target->ImageDesc.Left + target->ImageDesc.Width
         && target->ImageDesc.Top <= covered->ImageDesc.Top
         && covered->ImageDesc.Top + covered->ImageDesc.Height <=
                target->ImageDesc.Top + target->ImageDesc.Height) {
         return true;
     }
     return false;
 }

 static void disposeFrameIfNeeded(SkBitmap* bm, const SavedImage* cur, const SavedImage* next,
                                  SkBitmap* backup, SkColor color)
 {
     // We can skip disposal process if next frame is not transparent
     // and completely covers current area
     bool curTrans;
     int curDisposal;
     getTransparencyAndDisposalMethod(cur, &curTrans, &curDisposal);
     bool nextTrans;
     int nextDisposal;
     getTransparencyAndDisposalMethod(next, &nextTrans, &nextDisposal);
     if ((curDisposal == 2 || curDisposal == 3)
         && (nextTrans || !checkIfCover(next, cur))) {
         switch (curDisposal) {
         // restore to background color
         // -> 'background' means background under this image.
         case 2:
             fillRect(bm, cur->ImageDesc.Left, cur->ImageDesc.Top,
                      cur->ImageDesc.Width, cur->ImageDesc.Height,
                      color);
             break;

         // restore to previous
         case 3:
             bm->swap(*backup);
             break;
         }
     }

     // Save current image if next frame's disposal method == 3
     if (nextDisposal == 3) {
         const uint32_t* src = bm->getAddr32(0, 0);
         uint32_t* dst = backup->getAddr32(0, 0);
         int cnt = bm->width() * bm->height();
         memcpy(dst, src, cnt*sizeof(uint32_t));
     }
 }

 bool SkGIFMovie::onGetBitmap(SkBitmap* bm)
 {
     const GifFileType* gif = fGIF;
     if (NULL == gif)
         return false;

     if (gif->ImageCount < 1) {
         return false;
     }

     const int width = gif->SWidth;
     const int height = gif->SHeight;
     if (width <= 0 || height <= 0) {
         return false;
     }

     // no need to draw
     if (fLastDrawIndex >= 0 && fLastDrawIndex == fCurrIndex) {
         return true;
     }

     int startIndex = fLastDrawIndex + 1;
     if (fLastDrawIndex < 0 || !bm->readyToDraw()) {
         // first time

         startIndex = 0;

         // create bitmap
         bm->setConfig(SkBitmap::kARGB_8888_Config, width, height, 0);
         if (!bm->allocPixels(NULL)) {
             return false;
         }
         // create bitmap for backup
         fBackup.setConfig(SkBitmap::kARGB_8888_Config, width, height, 0);
         if (!fBackup.allocPixels(NULL)) {
             return false;
         }
     } else if (startIndex > fCurrIndex) {
         // rewind to 1st frame for repeat
         startIndex = 0;
     }

     int lastIndex = fCurrIndex;
     if (lastIndex < 0) {
         // first time
         lastIndex = 0;
     } else if (lastIndex > fGIF->ImageCount - 1) {
         // this block must not be reached.
         lastIndex = fGIF->ImageCount - 1;
     }

     SkColor bgColor = SkPackARGB32(0, 0, 0, 0);
     if (gif->SColorMap != NULL) {
         const GifColorType& col = gif->SColorMap->Colors[fGIF->SBackGroundColor];
         bgColor = SkColorSetARGB(0xFF, col.Red, col.Green, col.Blue);
     }

     static SkColor paintingColor = SkPackARGB32(0, 0, 0, 0);
     // draw each frames - not intelligent way
     for (int i = startIndex; i <= lastIndex; i++) {
         const SavedImage* cur = &fGIF->SavedImages[i];
         if (i == 0) {
             bool trans;
             int disposal;
             getTransparencyAndDisposalMethod(cur, &trans, &disposal);
             if (!trans && gif->SColorMap != NULL) {
                 paintingColor = bgColor;
             } else {
                 paintingColor = SkColorSetARGB(0, 0, 0, 0);
             }

             bm->eraseColor(paintingColor);
             fBackup.eraseColor(paintingColor);
         } else {
             // Dispose previous frame before move to next frame.
             const SavedImage* prev = &fGIF->SavedImages[i-1];
             disposeFrameIfNeeded(bm, prev, cur, &fBackup, paintingColor);
         }

         // Draw frame
         // We can skip this process if this index is not last and disposal
         // method == 2 or method == 3
         if (i == lastIndex || !checkIfWillBeCleared(cur)) {
             drawFrame(bm, cur, gif->SColorMap);
         }
     }

     // save index
     fLastDrawIndex = lastIndex;
     return true;
 }

 ///////////////////////////////////////////////////////////////////////////////

 #include "SkTRegistry.h"

 SkMovie* Factory(SkStream* stream) {
     char buf[GIF_STAMP_LEN];
     if (stream->read(buf, GIF_STAMP_LEN) == GIF_STAMP_LEN) {
         if (memcmp(GIF_STAMP,   buf, GIF_STAMP_LEN) == 0 ||
                 memcmp(GIF87_STAMP, buf, GIF_STAMP_LEN) == 0 ||
                 memcmp(GIF89_STAMP, buf, GIF_STAMP_LEN) == 0) {
             // must rewind here, since our construct wants to re-read the data
             stream->rewind();
             return SkNEW_ARGS(SkGIFMovie, (stream));
         }
     }
     return NULL;
 }

 static SkTRegistry<SkMovie*, SkStream*> gReg(Factory);

	/*
	* Copyright 2006 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.
	*/


	#include "SkMovie.h"
	#include "SkColor.h"
	#include "SkColorPriv.h"
	#include "SkStream.h"
	#include "SkTemplates.h"
	#include "SkUtils.h"

	#include "gif_lib.h"

	class SkGIFMovie : public SkMovie {
	public:
	SkGIFMovie(SkStream* stream);
	virtual ~SkGIFMovie();

	protected:
	virtual bool onGetInfo(Info*);
	virtual bool onSetTime(SkMSec);
	virtual bool onGetBitmap(SkBitmap*);

	private:
	GifFileType* fGIF;
	int fCurrIndex;
	int fLastDrawIndex;
	SkBitmap fBackup;
	};

	static int Decode(GifFileType* fileType, GifByteType* out, int size) {
	SkStream* stream = (SkStream*) fileType->UserData;
	return (int) stream->read(out, size);
	}

	SkGIFMovie::SkGIFMovie(SkStream* stream)
	{
	fGIF = DGifOpen( stream, Decode );
	if (NULL == fGIF)
	return;

	if (DGifSlurp(fGIF) != GIF_OK)
	{
	DGifCloseFile(fGIF);
	fGIF = NULL;
	}
	fCurrIndex = -1;
	fLastDrawIndex = -1;
	}

	SkGIFMovie::~SkGIFMovie()
	{
	if (fGIF)
	DGifCloseFile(fGIF);
	}

	static SkMSec savedimage_duration(const SavedImage* image)
	{
	for (int j = 0; j < image->ExtensionBlockCount; j++)
	{
	if (image->ExtensionBlocks[j].Function == GRAPHICS_EXT_FUNC_CODE)
	{
	int size = image->ExtensionBlocks[j].ByteCount;
	SkASSERT(size >= 4);
	const uint8_t* b = (const uint8_t*)image->ExtensionBlocks[j].Bytes;
	return ((b[2] << 8) \| b[1]) * 10;
	}
	}
	return 0;
	}

	bool SkGIFMovie::onGetInfo(Info* info)
	{
	if (NULL == fGIF)
	return false;

	SkMSec dur = 0;
	for (int i = 0; i < fGIF->ImageCount; i++)
	dur += savedimage_duration(&fGIF->SavedImages[i]);

	info->fDuration = dur;
	info->fWidth = fGIF->SWidth;
	info->fHeight = fGIF->SHeight;
	info->fIsOpaque = false; // how to compute?
	return true;
	}

	bool SkGIFMovie::onSetTime(SkMSec time)
	{
	if (NULL == fGIF)
	return false;

	SkMSec dur = 0;
	for (int i = 0; i < fGIF->ImageCount; i++)
	{
	dur += savedimage_duration(&fGIF->SavedImages[i]);
	if (dur >= time)
	{
	fCurrIndex = i;
	return fLastDrawIndex != fCurrIndex;
	}
	}
	fCurrIndex = fGIF->ImageCount - 1;
	return true;
	}

	static void copyLine(uint32_t* dst, const unsigned char* src, const ColorMapObject* cmap,
	int transparent, int width)
	{
	for (; width > 0; width--, src++, dst++) {
	if (*src != transparent) {
	const GifColorType& col = cmap->Colors[*src];
	*dst = SkPackARGB32(0xFF, col.Red, col.Green, col.Blue);
	}
	}
	}

	static void copyInterlaceGroup(SkBitmap* bm, const unsigned char*& src,
	const ColorMapObject* cmap, int transparent, int copyWidth,
	int copyHeight, const GifImageDesc& imageDesc, int rowStep,
	int startRow)
	{
	int row;
	// every 'rowStep'th row, starting with row 'startRow'
	for (row = startRow; row < copyHeight; row += rowStep) {
	uint32_t* dst = bm->getAddr32(imageDesc.Left, imageDesc.Top + row);
	copyLine(dst, src, cmap, transparent, copyWidth);
	src += imageDesc.Width;
	}

	// pad for rest height
	src += imageDesc.Width * ((imageDesc.Height - row + rowStep - 1) / rowStep);
	}

	static void blitInterlace(SkBitmap* bm, const SavedImage* frame, const ColorMapObject* cmap,
	int transparent)
	{
	int width = bm->width();
	int height = bm->height();
	GifWord copyWidth = frame->ImageDesc.Width;
	if (frame->ImageDesc.Left + copyWidth > width) {
	copyWidth = width - frame->ImageDesc.Left;
	}

	GifWord copyHeight = frame->ImageDesc.Height;
	if (frame->ImageDesc.Top + copyHeight > height) {
	copyHeight = height - frame->ImageDesc.Top;
	}

	// deinterlace
	const unsigned char* src = (unsigned char*)frame->RasterBits;

	// group 1 - every 8th row, starting with row 0
	copyInterlaceGroup(bm, src, cmap, transparent, copyWidth, copyHeight, frame->ImageDesc, 8, 0);

	// group 2 - every 8th row, starting with row 4
	copyInterlaceGroup(bm, src, cmap, transparent, copyWidth, copyHeight, frame->ImageDesc, 8, 4);

	// group 3 - every 4th row, starting with row 2
	copyInterlaceGroup(bm, src, cmap, transparent, copyWidth, copyHeight, frame->ImageDesc, 4, 2);

	copyInterlaceGroup(bm, src, cmap, transparent, copyWidth, copyHeight, frame->ImageDesc, 2, 1);
	}

	static void blitNormal(SkBitmap* bm, const SavedImage* frame, const ColorMapObject* cmap,
	int transparent)
	{
	int width = bm->width();
	int height = bm->height();
	const unsigned char* src = (unsigned char*)frame->RasterBits;
	uint32_t* dst = bm->getAddr32(frame->ImageDesc.Left, frame->ImageDesc.Top);
	GifWord copyWidth = frame->ImageDesc.Width;
	if (frame->ImageDesc.Left + copyWidth > width) {
	copyWidth = width - frame->ImageDesc.Left;
	}

	GifWord copyHeight = frame->ImageDesc.Height;
	if (frame->ImageDesc.Top + copyHeight > height) {
	copyHeight = height - frame->ImageDesc.Top;
	}

	int srcPad, dstPad;
	dstPad = width - copyWidth;
	srcPad = frame->ImageDesc.Width - copyWidth;
	for (; copyHeight > 0; copyHeight--) {
	copyLine(dst, src, cmap, transparent, copyWidth);
	src += frame->ImageDesc.Width;
	dst += width;
	}
	}

	static void fillRect(SkBitmap* bm, GifWord left, GifWord top, GifWord width, GifWord height,
	uint32_t col)
	{
	int bmWidth = bm->width();
	int bmHeight = bm->height();
	uint32_t* dst = bm->getAddr32(left, top);
	GifWord copyWidth = width;
	if (left + copyWidth > bmWidth) {
	copyWidth = bmWidth - left;
	}

	GifWord copyHeight = height;
	if (top + copyHeight > bmHeight) {
	copyHeight = bmHeight - top;
	}

	for (; copyHeight > 0; copyHeight--) {
	sk_memset32(dst, col, copyWidth);
	dst += bmWidth;
	}
	}

	static void drawFrame(SkBitmap* bm, const SavedImage* frame, const ColorMapObject* cmap)
	{
	int transparent = -1;

	for (int i = 0; i < frame->ExtensionBlockCount; ++i) {
	ExtensionBlock* eb = frame->ExtensionBlocks + i;
	if (eb->Function == GRAPHICS_EXT_FUNC_CODE &&
	eb->ByteCount == 4) {
	bool has_transparency = ((eb->Bytes[0] & 1) == 1);
	if (has_transparency) {
	transparent = (unsigned char)eb->Bytes[3];
	}
	}
	}

	if (frame->ImageDesc.ColorMap != NULL) {
	// use local color table
	cmap = frame->ImageDesc.ColorMap;
	}

	if (cmap == NULL \|\| cmap->ColorCount != (1 << cmap->BitsPerPixel)) {
	SkDEBUGFAIL("bad colortable setup");
	return;
	}

	if (frame->ImageDesc.Interlace) {
	blitInterlace(bm, frame, cmap, transparent);
	} else {
	blitNormal(bm, frame, cmap, transparent);
	}
	}

	static bool checkIfWillBeCleared(const SavedImage* frame)
	{
	for (int i = 0; i < frame->ExtensionBlockCount; ++i) {
	ExtensionBlock* eb = frame->ExtensionBlocks + i;
	if (eb->Function == GRAPHICS_EXT_FUNC_CODE &&
	eb->ByteCount == 4) {
	// check disposal method
	int disposal = ((eb->Bytes[0] >> 2) & 7);
	if (disposal == 2 \|\| disposal == 3) {
	return true;
	}
	}
	}
	return false;
	}

	static void getTransparencyAndDisposalMethod(const SavedImage* frame, bool* trans, int* disposal)
	{
	*trans = false;
	*disposal = 0;
	for (int i = 0; i < frame->ExtensionBlockCount; ++i) {
	ExtensionBlock* eb = frame->ExtensionBlocks + i;
	if (eb->Function == GRAPHICS_EXT_FUNC_CODE &&
	eb->ByteCount == 4) {
	*trans = ((eb->Bytes[0] & 1) == 1);
	*disposal = ((eb->Bytes[0] >> 2) & 7);
	}
	}
	}

	// return true if area of 'target' is completely covers area of 'covered'
	static bool checkIfCover(const SavedImage* target, const SavedImage* covered)
	{
	if (target->ImageDesc.Left <= covered->ImageDesc.Left
	&& covered->ImageDesc.Left + covered->ImageDesc.Width <=
	target->ImageDesc.Left + target->ImageDesc.Width
	&& target->ImageDesc.Top <= covered->ImageDesc.Top
	&& covered->ImageDesc.Top + covered->ImageDesc.Height <=
	target->ImageDesc.Top + target->ImageDesc.Height) {
	return true;
	}
	return false;
	}

	static void disposeFrameIfNeeded(SkBitmap* bm, const SavedImage* cur, const SavedImage* next,
	SkBitmap* backup, SkColor color)
	{
	// We can skip disposal process if next frame is not transparent
	// and completely covers current area
	bool curTrans;
	int curDisposal;
	getTransparencyAndDisposalMethod(cur, &curTrans, &curDisposal);
	bool nextTrans;
	int nextDisposal;
	getTransparencyAndDisposalMethod(next, &nextTrans, &nextDisposal);
	if ((curDisposal == 2 \|\| curDisposal == 3)
	&& (nextTrans \|\| !checkIfCover(next, cur))) {
	switch (curDisposal) {
	// restore to background color
	// -> 'background' means background under this image.
	case 2:
	fillRect(bm, cur->ImageDesc.Left, cur->ImageDesc.Top,
	cur->ImageDesc.Width, cur->ImageDesc.Height,
	color);
	break;

	// restore to previous
	case 3:
	bm->swap(*backup);
	break;
	}
	}

	// Save current image if next frame's disposal method == 3
	if (nextDisposal == 3) {
	const uint32_t* src = bm->getAddr32(0, 0);
	uint32_t* dst = backup->getAddr32(0, 0);
	int cnt = bm->width() * bm->height();
	memcpy(dst, src, cnt*sizeof(uint32_t));
	}
	}

	bool SkGIFMovie::onGetBitmap(SkBitmap* bm)
	{
	const GifFileType* gif = fGIF;
	if (NULL == gif)
	return false;

	if (gif->ImageCount < 1) {
	return false;
	}

	const int width = gif->SWidth;
	const int height = gif->SHeight;
	if (width <= 0 \|\| height <= 0) {
	return false;
	}

	// no need to draw
	if (fLastDrawIndex >= 0 && fLastDrawIndex == fCurrIndex) {
	return true;
	}

	int startIndex = fLastDrawIndex + 1;
	if (fLastDrawIndex < 0 \|\| !bm->readyToDraw()) {
	// first time

	startIndex = 0;

	// create bitmap
	bm->setConfig(SkBitmap::kARGB_8888_Config, width, height, 0);
	if (!bm->allocPixels(NULL)) {
	return false;
	}
	// create bitmap for backup
	fBackup.setConfig(SkBitmap::kARGB_8888_Config, width, height, 0);
	if (!fBackup.allocPixels(NULL)) {
	return false;
	}
	} else if (startIndex > fCurrIndex) {
	// rewind to 1st frame for repeat
	startIndex = 0;
	}

	int lastIndex = fCurrIndex;
	if (lastIndex < 0) {
	// first time
	lastIndex = 0;
	} else if (lastIndex > fGIF->ImageCount - 1) {
	// this block must not be reached.
	lastIndex = fGIF->ImageCount - 1;
	}

	SkColor bgColor = SkPackARGB32(0, 0, 0, 0);
	if (gif->SColorMap != NULL) {
	const GifColorType& col = gif->SColorMap->Colors[fGIF->SBackGroundColor];
	bgColor = SkColorSetARGB(0xFF, col.Red, col.Green, col.Blue);
	}

	static SkColor paintingColor = SkPackARGB32(0, 0, 0, 0);
	// draw each frames - not intelligent way
	for (int i = startIndex; i <= lastIndex; i++) {
	const SavedImage* cur = &fGIF->SavedImages[i];
	if (i == 0) {
	bool trans;
	int disposal;
	getTransparencyAndDisposalMethod(cur, &trans, &disposal);
	if (!trans && gif->SColorMap != NULL) {
	paintingColor = bgColor;
	} else {
	paintingColor = SkColorSetARGB(0, 0, 0, 0);
	}

	bm->eraseColor(paintingColor);
	fBackup.eraseColor(paintingColor);
	} else {
	// Dispose previous frame before move to next frame.
	const SavedImage* prev = &fGIF->SavedImages[i-1];
	disposeFrameIfNeeded(bm, prev, cur, &fBackup, paintingColor);
	}

	// Draw frame
	// We can skip this process if this index is not last and disposal
	// method == 2 or method == 3
	if (i == lastIndex \|\| !checkIfWillBeCleared(cur)) {
	drawFrame(bm, cur, gif->SColorMap);
	}
	}

	// save index
	fLastDrawIndex = lastIndex;
	return true;
	}

	///////////////////////////////////////////////////////////////////////////////

	#include "SkTRegistry.h"

	SkMovie* Factory(SkStream* stream) {
	char buf[GIF_STAMP_LEN];
	if (stream->read(buf, GIF_STAMP_LEN) == GIF_STAMP_LEN) {
	if (memcmp(GIF_STAMP, buf, GIF_STAMP_LEN) == 0 \|\|
	memcmp(GIF87_STAMP, buf, GIF_STAMP_LEN) == 0 \|\|
	memcmp(GIF89_STAMP, buf, GIF_STAMP_LEN) == 0) {
	// must rewind here, since our construct wants to re-read the data
	stream->rewind();
	return SkNEW_ARGS(SkGIFMovie, (stream));
	}
	}
	return NULL;
	}

	static SkTRegistry<SkMovie, SkStream> gReg(Factory);