src/images/SkImageDecoder_libbmp.cpp

/*
 * Copyright 2007, The Android Open Source Project
 *
 * 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 "bmpdecoderhelper.h"
#include "SkImageDecoder.h"
#include "SkScaledBitmapSampler.h"
#include "SkStream.h"
#include "SkColorPriv.h"
#include "SkTDArray.h"
#include "SkTRegistry.h"

class SkBMPImageDecoder : public SkImageDecoder {
public:
    SkBMPImageDecoder() {}
    
    virtual Format getFormat() const {
        return kBMP_Format;
    }

protected:
    virtual bool onDecode(SkStream* stream, SkBitmap* bm,
                          SkBitmap::Config pref, Mode mode);
};

static SkImageDecoder* Factory(SkStream* stream) {
    static const char kBmpMagic[] = { 'B', 'M' };
    
    size_t len = stream->getLength();
    char buffer[sizeof(kBmpMagic)];
    
    if (len > sizeof(kBmpMagic) &&
            stream->read(buffer, sizeof(kBmpMagic)) == sizeof(kBmpMagic) &&
            !memcmp(buffer, kBmpMagic, sizeof(kBmpMagic))) {
        return SkNEW(SkBMPImageDecoder);
    }
    return NULL;
}

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

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

class SkBmpDecoderCallback : public image_codec::BmpDecoderCallback {
public:
    // we don't copy the bitmap, just remember the pointer
    SkBmpDecoderCallback(bool justBounds) : fJustBounds(justBounds) {}

    // override from BmpDecoderCallback
    virtual uint8* SetSize(int width, int height) {
        fWidth = width;
        fHeight = height;
        if (fJustBounds) {
            return NULL;
        }
        
        fRGB.setCount(width * height * 3);  // 3 == r, g, b
        return fRGB.begin();
    }

    int width() const { return fWidth; }
    int height() const { return fHeight; }
    uint8_t* rgb() const { return fRGB.begin(); }

private:
    SkTDArray<uint8_t> fRGB;
    int fWidth;
    int fHeight;
    bool fJustBounds;
};

bool SkBMPImageDecoder::onDecode(SkStream* stream, SkBitmap* bm,
                                 SkBitmap::Config prefConfig, Mode mode) {

    size_t length = stream->getLength();
    SkAutoMalloc storage(length);
    
    if (stream->read(storage.get(), length) != length) {
        return false;
    }
    
    const bool justBounds = SkImageDecoder::kDecodeBounds_Mode == mode;
    SkBmpDecoderCallback callback(justBounds);

    // Now decode the BMP into callback's rgb() array [r,g,b, r,g,b, ...]
    {
        image_codec::BmpDecoderHelper helper;
        const int max_pixels = 16383*16383; // max width*height
        if (!helper.DecodeImage((const char*)storage.get(), length,
                                max_pixels, &callback)) {
            return false;
        }
    }
    
    // we don't need this anymore, so free it now (before we try to allocate
    // the bitmap's pixels) rather than waiting for its destructor
    storage.free();
    
    int width = callback.width();
    int height = callback.height();
    SkBitmap::Config config = SkBitmap::kARGB_8888_Config;
    
    // only accept prefConfig if it makes sense for us
    if (SkBitmap::kARGB_4444_Config == prefConfig ||
            SkBitmap::kRGB_565_Config == config) {
        config = prefConfig;
    }

    SkScaledBitmapSampler sampler(width, height, getSampleSize());

    bm->setConfig(config, sampler.scaledWidth(), sampler.scaledHeight());
    bm->setIsOpaque(true);
    if (justBounds) {
        return true;
    }

    if (!this->allocPixelRef(bm, NULL)) {
        return false;
    }
    
    SkAutoLockPixels alp(*bm);
    
    if (!sampler.begin(bm, SkScaledBitmapSampler::kRGB, getDitherImage())) {
        return false;
    }

    const int srcRowBytes = width * 3;
    const int dstHeight = sampler.scaledHeight();
    const uint8_t* srcRow = callback.rgb();
    
    srcRow += sampler.srcY0() * srcRowBytes;
    for (int y = 0; y < dstHeight; y++) {
        sampler.next(srcRow);
        srcRow += sampler.srcDY() * srcRowBytes;
    }
    return true;
}