path: root/skia/images/SkImageDecoder_libpng.cpp

/* libs/graphics/images/SkImageDecoder_libpng.cpp
**
** Copyright 2006, Google Inc.
**
** Licensed under the Apache License, Version 2.0 (the "License"); 
** you may not use this file except in compliance with the License. 
** You may obtain a copy of the License at 
**
**     http://www.apache.org/licenses/LICENSE-2.0 
**
** Unless required by applicable law or agreed to in writing, software 
** distributed under the License is distributed on an "AS IS" BASIS, 
** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
** See the License for the specific language governing permissions and 
** limitations under the License.
*/

#include "SkImageDecoder.h"
#include "SkColor.h"
#include "SkColorPriv.h"
#include "SkDither.h"
#include "SkMath.h"
#include "SkScaledBitmapSampler.h"
#include "SkStream.h"
#include "SkTemplates.h"
#include "SkUtils.h"

extern "C" {
#include "png.h"
}

class SkPNGImageDecoder : public SkImageDecoder {
public:
    virtual Format getFormat() const {
        return kPNG_Format;
    }
    
protected:
    virtual bool onDecode(SkStream* stream, SkBitmap* bm,
                          SkBitmap::Config pref, Mode);
};

#ifndef png_jmpbuf
#  define png_jmpbuf(png_ptr) ((png_ptr)->jmpbuf)
#endif

#define PNG_BYTES_TO_CHECK 4

/* Automatically clean up after throwing an exception */
struct PNGAutoClean {
    PNGAutoClean(png_structp p, png_infop i): png_ptr(p), info_ptr(i) {}
    ~PNGAutoClean() {
        png_destroy_read_struct(&png_ptr, &info_ptr, png_infopp_NULL);
    }
private:
    png_structp png_ptr;
    png_infop info_ptr;
};

SkImageDecoder* SkImageDecoder_PNG_Factory(SkStream* stream) {
    char buf[PNG_BYTES_TO_CHECK];
    if (stream->read(buf, PNG_BYTES_TO_CHECK) == PNG_BYTES_TO_CHECK &&
            !png_sig_cmp((png_bytep) buf, (png_size_t)0, PNG_BYTES_TO_CHECK)) {
        return SkNEW(SkPNGImageDecoder);
    }
    return NULL;
}

static void sk_read_fn(png_structp png_ptr, png_bytep data, png_size_t length) {
    SkStream* sk_stream = (SkStream*) png_ptr->io_ptr;
    size_t bytes = sk_stream->read(data, length);
    if (bytes != length) {
        png_error(png_ptr, "Read Error!");
    }
}

static int sk_read_user_chunk(png_structp png_ptr, png_unknown_chunkp chunk) {
    SkImageDecoder::Peeker* peeker =
                    (SkImageDecoder::Peeker*)png_get_user_chunk_ptr(png_ptr);
    // peek() returning true means continue decoding
    return peeker->peek((const char*)chunk->name, chunk->data, chunk->size) ?
            1 : -1;
}

static void sk_error_fn(png_structp png_ptr, png_const_charp msg) {
    SkDebugf("------ png error %s\n", msg);
    longjmp(png_jmpbuf(png_ptr), 1);
}

static void skip_src_rows(png_structp png_ptr, uint8_t storage[], int count) {
    for (int i = 0; i < count; i++) {
        uint8_t* tmp = storage;
        png_read_rows(png_ptr, &tmp, png_bytepp_NULL, 1);
    }
}

static bool pos_le(int value, int max) {
    return value > 0 && value <= max;
}

bool SkPNGImageDecoder::onDecode(SkStream* sk_stream, SkBitmap* decodedBitmap,
                                 SkBitmap::Config prefConfig, Mode mode) {
//    SkAutoTrace    apr("SkPNGImageDecoder::onDecode");

    /* Create and initialize the png_struct with the desired error handler
    * functions.  If you want to use the default stderr and longjump method,
    * you can supply NULL for the last three parameters.  We also supply the
    * the compiler header file version, so that we know if the application
    * was compiled with a compatible version of the library.  */
    png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING,
        NULL, sk_error_fn, NULL);
    //   png_voidp user_error_ptr, user_error_fn, user_warning_fn);
    if (png_ptr == NULL) {
        return false;
    }

    /* Allocate/initialize the memory for image information. */
    png_infop info_ptr = png_create_info_struct(png_ptr);
    if (info_ptr == NULL) {
        png_destroy_read_struct(&png_ptr, png_infopp_NULL, png_infopp_NULL);
        return false;
    }

    PNGAutoClean autoClean(png_ptr, info_ptr);

    /* Set error handling if you are using the setjmp/longjmp method (this is
    * the normal method of doing things with libpng).  REQUIRED unless you
    * set up your own error handlers in the png_create_read_struct() earlier.
    */
    if (setjmp(png_jmpbuf(png_ptr))) {
        return false;
    }

    /* If you are using replacement read functions, instead of calling
    * png_init_io() here you would call:
    */
    png_set_read_fn(png_ptr, (void *)sk_stream, sk_read_fn);
    /* where user_io_ptr is a structure you want available to the callbacks */
    /* If we have already read some of the signature */
//  png_set_sig_bytes(png_ptr, 0 /* sig_read */ );

    // hookup our peeker so we can see any user-chunks the caller may be interested in
    png_set_keep_unknown_chunks(png_ptr, PNG_HANDLE_CHUNK_ALWAYS, (png_byte*)"", 0);
    if (this->getPeeker()) {
        png_set_read_user_chunk_fn(png_ptr, (png_voidp)this->getPeeker(), sk_read_user_chunk);
    }

    /* The call to png_read_info() gives us all of the information from the
    * PNG file before the first IDAT (image data chunk). */
    png_read_info(png_ptr, info_ptr);
    png_uint_32 origWidth, origHeight;
    int bit_depth, color_type, interlace_type;
    png_get_IHDR(png_ptr, info_ptr, &origWidth, &origHeight, &bit_depth, &color_type,
        &interlace_type, int_p_NULL, int_p_NULL);

    SkBitmap::Config    config;
    bool                hasAlpha = false;
    bool                doDither = this->getDitherImage();
    
    // check for sBIT chunk data, in case we should disable dithering because
    // our data is not truely 8bits per component
    if (doDither) {
#if 0
        SkDebugf("----- sBIT %d %d %d %d\n", info_ptr->sig_bit.red,
                 info_ptr->sig_bit.green, info_ptr->sig_bit.blue,
                 info_ptr->sig_bit.alpha);
#endif
        // 0 seems to indicate no information available
        if (pos_le(info_ptr->sig_bit.red, SK_R16_BITS) &&
                pos_le(info_ptr->sig_bit.green, SK_G16_BITS) &&
                pos_le(info_ptr->sig_bit.blue, SK_B16_BITS)) {
            doDither = false;
        }
    }
    
    if (color_type == PNG_COLOR_TYPE_PALETTE) {
        config = SkBitmap::kIndex8_Config;  // defer sniffing for hasAlpha
    } else {
        png_color_16p   transColor;
        
        png_get_tRNS(png_ptr, info_ptr, NULL, NULL, &transColor);
        
        if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS) ||
                PNG_COLOR_TYPE_RGB_ALPHA == color_type ||
                PNG_COLOR_TYPE_GRAY_ALPHA == color_type) {
            hasAlpha = true;
            config = SkBitmap::kARGB_8888_Config;
        } else {    // we get to choose the config
            config = prefConfig;
            if (config == SkBitmap::kNo_Config) {
                config = SkImageDecoder::GetDeviceConfig();
            }
            if (config != SkBitmap::kRGB_565_Config &&
                    config != SkBitmap::kARGB_4444_Config) {
                config = SkBitmap::kARGB_8888_Config;
            }
        }
    }
    
    if (!this->chooseFromOneChoice(config, origWidth, origHeight)) {
        return false;
    }
    
    const int sampleSize = this->getSampleSize();
    SkScaledBitmapSampler sampler(origWidth, origHeight, sampleSize);

    decodedBitmap->setConfig(config, sampler.scaledWidth(),
                             sampler.scaledHeight(), 0);
    if (SkImageDecoder::kDecodeBounds_Mode == mode) {
        return true;
    }
    
    // from here down we are concerned with colortables and pixels

    /* tell libpng to strip 16 bit/color files down to 8 bits/color */
    if (bit_depth == 16) {
        png_set_strip_16(png_ptr);
    }
    /* Extract multiple pixels with bit depths of 1, 2, and 4 from a single
    * byte into separate bytes (useful for paletted and grayscale images). */
    if (bit_depth < 8) {
        png_set_packing(png_ptr);
    }
    /* Expand grayscale images to the full 8 bits from 1, 2, or 4 bits/pixel */
    if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8) {
        png_set_gray_1_2_4_to_8(png_ptr);
    }

    /* Make a grayscale image into RGB. */
    if (color_type == PNG_COLOR_TYPE_GRAY ||
            color_type == PNG_COLOR_TYPE_GRAY_ALPHA) {
        png_set_gray_to_rgb(png_ptr);
    }

    // we track if we actually see a non-opaque pixels, since sometimes a PNG sets its colortype
    // to |= PNG_COLOR_MASK_ALPHA, but all of its pixels are in fact opaque. We care, since we
    // draw lots faster if we can flag the bitmap has being opaque
    bool reallyHasAlpha = false;

    SkColorTable* colorTable = NULL;

    if (color_type == PNG_COLOR_TYPE_PALETTE) {
        int num_palette;
        png_colorp palette;
        png_bytep trans;
        int num_trans;

        png_get_PLTE(png_ptr, info_ptr, &palette, &num_palette);
        
        /*  BUGGY IMAGE WORKAROUND
            
            We hit some images (e.g. fruit_.png) who contain bytes that are == colortable_count
            which is a problem since we use the byte as an index. To work around this we grow
            the colortable by 1 (if its < 256) and duplicate the last color into that slot.
        */
        int colorCount = num_palette + (num_palette < 256);

        colorTable = SkNEW_ARGS(SkColorTable, (colorCount));

        SkPMColor* colorPtr = colorTable->lockColors();
        if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS)) {
            png_get_tRNS(png_ptr, info_ptr, &trans, &num_trans, NULL);
            hasAlpha = (num_trans > 0);
        } else {
            num_trans = 0;
            colorTable->setFlags(colorTable->getFlags() | SkColorTable::kColorsAreOpaque_Flag);
        }        
        // check for bad images that might make us crash
        if (num_trans > num_palette) {
            num_trans = num_palette;
        }

        int index = 0;
        int transLessThanFF = 0;

        for (; index < num_trans; index++) {
            transLessThanFF |= (int)*trans - 0xFF;
            *colorPtr++ = SkPreMultiplyARGB(*trans++, palette->red, palette->green, palette->blue);
            palette++;
        }
        reallyHasAlpha |= (transLessThanFF < 0);

        for (; index < num_palette; index++) {
            *colorPtr++ = SkPackARGB32(0xFF, palette->red, palette->green, palette->blue);
            palette++;
        }

        // see BUGGY IMAGE WORKAROUND comment above
        if (num_palette < 256) {
            *colorPtr = colorPtr[-1];
        }
        colorTable->unlockColors(true);
    }
    
    SkAutoUnref aur(colorTable);

    if (!this->allocPixelRef(decodedBitmap, colorTable)) {
        delete colorTable;
        return false;
    }
    
    SkAutoLockPixels alp(*decodedBitmap);

    /* swap the RGBA or GA data to ARGB or AG (or BGRA to ABGR) */
//  if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
//      ; // png_set_swap_alpha(png_ptr);

    /* swap bytes of 16 bit files to least significant byte first */
    //   png_set_swap(png_ptr);

    /* Add filler (or alpha) byte (before/after each RGB triplet) */
    if (color_type == PNG_COLOR_TYPE_RGB || color_type == PNG_COLOR_TYPE_GRAY) {
        png_set_filler(png_ptr, 0xff, PNG_FILLER_AFTER);
    }

    /* Turn on interlace handling.  REQUIRED if you are not using
    * png_read_image().  To see how to handle interlacing passes,
    * see the png_read_row() method below:
    */
    const int number_passes = interlace_type != PNG_INTERLACE_NONE ? 
                        png_set_interlace_handling(png_ptr) : 1;

    /* Optional call to gamma correct and add the background to the palette
    * and update info structure.  REQUIRED if you are expecting libpng to
    * update the palette for you (ie you selected such a transform above).
    */
    png_read_update_info(png_ptr, info_ptr);

    if (SkBitmap::kIndex8_Config == config && 1 == sampleSize) {
        for (int i = 0; i < number_passes; i++) {
            for (png_uint_32 y = 0; y < origHeight; y++) {
                uint8_t* bmRow = decodedBitmap->getAddr8(0, y);
                png_read_rows(png_ptr, &bmRow, png_bytepp_NULL, 1);
            }
        }
    } else {
        SkScaledBitmapSampler::SrcConfig sc;
        int srcBytesPerPixel = 4;
        
        if (SkBitmap::kIndex8_Config == config) {
            sc = SkScaledBitmapSampler::kIndex;
            srcBytesPerPixel = 1;
        } else if (hasAlpha) {
            sc = SkScaledBitmapSampler::kRGBA;
        } else {
            sc = SkScaledBitmapSampler::kRGBX;
        }

        SkAutoMalloc storage(origWidth * srcBytesPerPixel);
        const int height = decodedBitmap->height();

        for (int i = 0; i < number_passes; i++) {
            if (!sampler.begin(decodedBitmap, sc, doDither)) {
                return false;
            }

            uint8_t* srcRow = (uint8_t*)storage.get();
            skip_src_rows(png_ptr, srcRow, sampler.srcY0());

            for (int y = 0; y < height; y++) {
                uint8_t* tmp = srcRow;
                png_read_rows(png_ptr, &tmp, png_bytepp_NULL, 1);
                reallyHasAlpha |= sampler.next(srcRow);
                if (y < height - 1) {
                    skip_src_rows(png_ptr, srcRow, sampler.srcDY() - 1);
                }
            }
            
            // skip the rest of the rows (if any)
            png_uint_32 read = (height - 1) * sampler.srcDY() +
                               sampler.srcY0() + 1;
            SkASSERT(read <= origHeight);
            skip_src_rows(png_ptr, srcRow, origHeight - read);
        }

        if (hasAlpha && !reallyHasAlpha) {
            SkDEBUGF(("Image doesn't really have alpha [%d %d]\n",
                      origWidth, origHeight));
        }
    }

    /* read rest of file, and get additional chunks in info_ptr - REQUIRED */
    png_read_end(png_ptr, info_ptr);

    decodedBitmap->setIsOpaque(!reallyHasAlpha);
    return true;
}

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

#ifdef SK_SUPPORT_IMAGE_ENCODE

#include "SkColorPriv.h"
#include "SkUnPreMultiply.h"

static void sk_write_fn(png_structp png_ptr, png_bytep data, png_size_t len) {
    SkWStream* sk_stream = (SkWStream*)png_ptr->io_ptr;
    if (!sk_stream->write(data, len)) {
        png_error(png_ptr, "sk_write_fn Error!");
    }
}

typedef void (*transform_scanline_proc)(const char* SK_RESTRICT src,
                                        int width, char* SK_RESTRICT dst);

static void transform_scanline_565(const char* SK_RESTRICT src, int width,
                                   char* SK_RESTRICT dst) {
    const uint16_t* SK_RESTRICT srcP = (const uint16_t*)src;    
    for (int i = 0; i < width; i++) {
        unsigned c = *srcP++;
        *dst++ = SkPacked16ToR32(c);
        *dst++ = SkPacked16ToG32(c);
        *dst++ = SkPacked16ToB32(c);
    }
}

static void transform_scanline_888(const char* SK_RESTRICT src, int width,
                                   char* SK_RESTRICT dst) {
    const SkPMColor* SK_RESTRICT srcP = (const SkPMColor*)src;    
    for (int i = 0; i < width; i++) {
        SkPMColor c = *srcP++;
        *dst++ = SkGetPackedR32(c);
        *dst++ = SkGetPackedG32(c);
        *dst++ = SkGetPackedB32(c);
    }
}

static void transform_scanline_444(const char* SK_RESTRICT src, int width,
                                   char* SK_RESTRICT dst) {
    const SkPMColor16* SK_RESTRICT srcP = (const SkPMColor16*)src;    
    for (int i = 0; i < width; i++) {
        SkPMColor16 c = *srcP++;
        *dst++ = SkPacked4444ToR32(c);
        *dst++ = SkPacked4444ToG32(c);
        *dst++ = SkPacked4444ToB32(c);
    }
}

static void transform_scanline_8888(const char* SK_RESTRICT src, int width,
                                    char* SK_RESTRICT dst) {
    const SkPMColor* SK_RESTRICT srcP = (const SkPMColor*)src;
    const SkUnPreMultiply::Scale* SK_RESTRICT table = 
                                              SkUnPreMultiply::GetScaleTable();

    for (int i = 0; i < width; i++) {
        SkPMColor c = *srcP++;
        unsigned a = SkGetPackedA32(c);
        unsigned r = SkGetPackedR32(c);
        unsigned g = SkGetPackedG32(c);
        unsigned b = SkGetPackedB32(c);

        if (0 != a && 255 != a) {
            SkUnPreMultiply::Scale scale = table[a];
            r = SkUnPreMultiply::ApplyScale(scale, r);
            g = SkUnPreMultiply::ApplyScale(scale, g);
            b = SkUnPreMultiply::ApplyScale(scale, b);
        }
        *dst++ = r;
        *dst++ = g;
        *dst++ = b;
        *dst++ = a;
    }
}

static void transform_scanline_4444(const char* SK_RESTRICT src, int width,
                                    char* SK_RESTRICT dst) {
    const SkPMColor16* SK_RESTRICT srcP = (const SkPMColor16*)src;
    const SkUnPreMultiply::Scale* SK_RESTRICT table = 
                                              SkUnPreMultiply::GetScaleTable();

    for (int i = 0; i < width; i++) {
        SkPMColor16 c = *srcP++;
        unsigned a = SkPacked4444ToA32(c);
        unsigned r = SkPacked4444ToR32(c);
        unsigned g = SkPacked4444ToG32(c);
        unsigned b = SkPacked4444ToB32(c);

        if (0 != a && 255 != a) {
            SkUnPreMultiply::Scale scale = table[a];
            r = SkUnPreMultiply::ApplyScale(scale, r);
            g = SkUnPreMultiply::ApplyScale(scale, g);
            b = SkUnPreMultiply::ApplyScale(scale, b);
        }
        *dst++ = r;
        *dst++ = g;
        *dst++ = b;
        *dst++ = a;
    }
}

static transform_scanline_proc choose_proc(SkBitmap::Config config,
                                           bool hasAlpha) {
    static const struct {
        SkBitmap::Config        fConfig;
        bool                    fHasAlpha;
        transform_scanline_proc fProc;
    } gMap[] = {
        { SkBitmap::kRGB_565_Config,    false,  transform_scanline_565 },
        { SkBitmap::kARGB_8888_Config,  false,  transform_scanline_888 },
        { SkBitmap::kARGB_8888_Config,  true,   transform_scanline_8888 },
        { SkBitmap::kARGB_4444_Config,  false,  transform_scanline_444 },
        { SkBitmap::kARGB_4444_Config,  true,   transform_scanline_4444 },
    };

    for (int i = SK_ARRAY_COUNT(gMap) - 1; i >= 0; --i) {
        if (gMap[i].fConfig == config && gMap[i].fHasAlpha == hasAlpha) {
            return gMap[i].fProc;
        }
    }
    sk_throw();
    return NULL;
}

class SkPNGImageEncoder : public SkImageEncoder {
protected:
    virtual bool onEncode(SkWStream* stream, const SkBitmap& bm, int quality);
};

bool SkPNGImageEncoder::onEncode(SkWStream* stream, const SkBitmap& bitmap,
                                 int /*quality*/) {
    SkBitmap::Config config = bitmap.getConfig();

    const bool hasAlpha = !bitmap.isOpaque();
    png_color_8 sig_bit;

    switch (config) {
        case SkBitmap::kARGB_8888_Config:
            sig_bit.red = 8;
            sig_bit.green = 8;
            sig_bit.blue = 8;
            sig_bit.alpha = hasAlpha ? 8 : 0;
            break;
        case SkBitmap::kARGB_4444_Config:
            sig_bit.red = 4;
            sig_bit.green = 4;
            sig_bit.blue = 4;
            sig_bit.alpha = hasAlpha ? 4 : 0;
            break;
        case SkBitmap::kRGB_565_Config:
            sig_bit.red = 5;
            sig_bit.green = 6;
            sig_bit.blue = 5;
            sig_bit.alpha = 0;
            break;
        default:
            SkDEBUGF(("SkPNGImageEncoder::onEncode can't encode %d config\n",
                      config));
            return false;
    }

    SkAutoLockPixels alp(bitmap);
    if (NULL == bitmap.getPixels()) {
        return false;
    }
    
    png_structp png_ptr;
    png_infop info_ptr;

    png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, sk_error_fn,
                                      NULL);
    if (NULL == png_ptr) {
        return false;
    }

    info_ptr = png_create_info_struct(png_ptr);
    if (NULL == info_ptr) {
        png_destroy_write_struct(&png_ptr,  png_infopp_NULL);
        return false;
    }

    /* Set error handling.  REQUIRED if you aren't supplying your own
    * error handling functions in the png_create_write_struct() call.
    */
    if (setjmp(png_jmpbuf(png_ptr))) {
        png_destroy_write_struct(&png_ptr, &info_ptr);
        return false;
    }

    png_set_write_fn(png_ptr, (void*)stream, sk_write_fn, png_flush_ptr_NULL);

    /* Set the image information here.  Width and height are up to 2^31,
    * bit_depth is one of 1, 2, 4, 8, or 16, but valid values also depend on
    * the color_type selected. color_type is one of PNG_COLOR_TYPE_GRAY,
    * PNG_COLOR_TYPE_GRAY_ALPHA, PNG_COLOR_TYPE_PALETTE, PNG_COLOR_TYPE_RGB,
    * or PNG_COLOR_TYPE_RGB_ALPHA.  interlace is either PNG_INTERLACE_NONE or
    * PNG_INTERLACE_ADAM7, and the compression_type and filter_type MUST
    * currently be PNG_COMPRESSION_TYPE_BASE and PNG_FILTER_TYPE_BASE. REQUIRED
    */

    png_set_IHDR(png_ptr, info_ptr, bitmap.width(), bitmap.height(), 8,
                 hasAlpha ? PNG_COLOR_TYPE_RGB_ALPHA : PNG_COLOR_TYPE_RGB,
                 PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_BASE,
                 PNG_FILTER_TYPE_BASE);

#if 0   // need to support this some day <reed>
    /* set the palette if there is one.  REQUIRED for indexed-color images */
    palette = (png_colorp)png_malloc(png_ptr, PNG_MAX_PALETTE_LENGTH
             * png_sizeof (png_color));
    /* ... set palette colors ... */
    png_set_PLTE(png_ptr, info_ptr, palette, PNG_MAX_PALETTE_LENGTH);
    /* You must not free palette here, because png_set_PLTE only makes a link to
      the palette that you malloced.  Wait until you are about to destroy
      the png structure. */
#endif

    png_set_sBIT(png_ptr, info_ptr, &sig_bit);
    png_write_info(png_ptr, info_ptr);

    const char* srcImage = (const char*)bitmap.getPixels();
    SkAutoSMalloc<1024> rowStorage(bitmap.width() << 2);
    char* storage = (char*)rowStorage.get();
    transform_scanline_proc proc = choose_proc(config, hasAlpha);

    for (int y = 0; y < bitmap.height(); y++) {
        png_bytep row_ptr = (png_bytep)storage;
        proc(srcImage, bitmap.width(), storage);
        png_write_rows(png_ptr, &row_ptr, 1);
        srcImage += bitmap.rowBytes();
    }

    png_write_end(png_ptr, info_ptr);

#if 0
    /* If you png_malloced a palette, free it here (don't free info_ptr->palette,
      as recommended in versions 1.0.5m and earlier of this example; if
      libpng mallocs info_ptr->palette, libpng will free it).  If you
      allocated it with malloc() instead of png_malloc(), use free() instead
      of png_free(). */
    png_free(png_ptr, palette);
#endif

    /* clean up after the write, and free any memory allocated */
    png_destroy_write_struct(&png_ptr, &info_ptr);
    return true;
}

SkImageEncoder* SkImageEncoder_PNG_Factory();
SkImageEncoder* SkImageEncoder_PNG_Factory() {
    return SkNEW(SkPNGImageEncoder);
}

#endif /* SK_SUPPORT_IMAGE_ENCODE */