pngimagereader.java

java1.6众多例子参考

    private static void decodeSubFilter(byte[] curr, int coff, int count,
                                        int bpp) {
        for (int i = bpp; i < count; i++) {
            int val;

            val = curr[i + coff] & 0xff;
            val += curr[i + coff - bpp] & 0xff;

            curr[i + coff] = (byte)val;
        }
    }

    private static void decodeUpFilter(byte[] curr, int coff,
                                       byte[] prev, int poff,
                                       int count) {
        for (int i = 0; i < count; i++) {
            int raw = curr[i + coff] & 0xff;
            int prior = prev[i + poff] & 0xff;

            curr[i + coff] = (byte)(raw + prior);
        }
    }

    private static void decodeAverageFilter(byte[] curr, int coff,
                                            byte[] prev, int poff,
                                            int count, int bpp) {
        int raw, priorPixel, priorRow;

        for (int i = 0; i < bpp; i++) {
            raw = curr[i + coff] & 0xff;
            priorRow = prev[i + poff] & 0xff;
            
            curr[i + coff] = (byte)(raw + priorRow/2);
        }

        for (int i = bpp; i < count; i++) {
            raw = curr[i + coff] & 0xff;
            priorPixel = curr[i + coff - bpp] & 0xff;
            priorRow = prev[i + poff] & 0xff;
            
            curr[i + coff] = (byte)(raw + (priorPixel + priorRow)/2);
        }
    }

    private static int paethPredictor(int a, int b, int c) {
        int p = a + b - c;
        int pa = Math.abs(p - a);
        int pb = Math.abs(p - b);
        int pc = Math.abs(p - c);

        if ((pa <= pb) && (pa <= pc)) {
            return a;
        } else if (pb <= pc) {
            return b;
        } else {
            return c;
        }
    } 

    private static void decodePaethFilter(byte[] curr, int coff,
                                          byte[] prev, int poff,
                                          int count, int bpp) {
        int raw, priorPixel, priorRow, priorRowPixel;

        for (int i = 0; i < bpp; i++) {
            raw = curr[i + coff] & 0xff;
            priorRow = prev[i + poff] & 0xff;

            curr[i + coff] = (byte)(raw + priorRow);
        }

        for (int i = bpp; i < count; i++) {
            raw = curr[i + coff] & 0xff;
            priorPixel = curr[i + coff - bpp] & 0xff;
            priorRow = prev[i + poff] & 0xff;
            priorRowPixel = prev[i + poff - bpp] & 0xff;

            curr[i + coff] = (byte)(raw + paethPredictor(priorPixel,
                                                         priorRow,
                                                         priorRowPixel));
        }
    }

    private static final int[][] bandOffsets = {
        null,
        { 0 }, // G
        { 0, 1 }, // GA in GA order
        { 0, 1, 2 }, // RGB in RGB order
        { 0, 1, 2, 3 } // RGBA in RGBA order
    };

    private WritableRaster createRaster(int width, int height, int bands,
                                        int scanlineStride,
                                        int bitDepth) {

        DataBuffer dataBuffer;
        WritableRaster ras = null;
        Point origin = new Point(0, 0);
        if ((bitDepth < 8) && (bands == 1)) {
            dataBuffer = new DataBufferByte(height*scanlineStride);
            ras = Raster.createPackedRaster(dataBuffer,
                                            width, height,
                                            bitDepth,
                                            origin);
        } else if (bitDepth <= 8) {
            dataBuffer = new DataBufferByte(height*scanlineStride);
            ras = Raster.createInterleavedRaster(dataBuffer,
                                                 width, height,
                                                 scanlineStride,
                                                 bands,
                                                 bandOffsets[bands],
                                                 origin);
        } else {
            dataBuffer = new DataBufferUShort(height*scanlineStride);
            ras = Raster.createInterleavedRaster(dataBuffer,
                                                 width, height,
                                                 scanlineStride,
                                                 bands,
                                                 bandOffsets[bands],
                                                 origin);
        }

        return ras;
    }

    private void skipPass(int passWidth, int passHeight)
        throws IOException, IIOException  {
        if ((passWidth == 0) || (passHeight == 0)) {
            return;
        }

        int inputBands = inputBandsForColorType[metadata.IHDR_colorType];
        int bytesPerRow = (inputBands*passWidth*metadata.IHDR_bitDepth + 7)/8;

        // Read the image row-by-row
        for (int srcY = 0; srcY < passHeight; srcY++) {
            // Skip filter byte and the remaining row bytes
            pixelStream.skipBytes(1 + bytesPerRow);

            // If read has been aborted, just return
            // processReadAborted will be called later
            if (abortRequested()) {
                return;
            }
        }
    }

    private void updateImageProgress(int newPixels) {
        pixelsDone += newPixels;
        processImageProgress(100.0F*pixelsDone/totalPixels);
    }

    private void decodePass(int passNum,
                            int xStart, int yStart,
                            int xStep, int yStep,
                            int passWidth, int passHeight) throws IOException {

        if ((passWidth == 0) || (passHeight == 0)) {
            return;
        }

        WritableRaster imRas = theImage.getWritableTile(0, 0);
        int dstMinX = imRas.getMinX();
        int dstMaxX = dstMinX + imRas.getWidth() - 1;
        int dstMinY = imRas.getMinY();
        int dstMaxY = dstMinY + imRas.getHeight() - 1;

        // Determine which pixels will be updated in this pass
        int[] vals =
          ReaderUtil.computeUpdatedPixels(sourceRegion,
                                          destinationOffset,
                                          dstMinX, dstMinY,
                                          dstMaxX, dstMaxY,
                                          sourceXSubsampling,
                                          sourceYSubsampling,
                                          xStart, yStart,
                                          passWidth, passHeight,
                                          xStep, yStep);
        int updateMinX = vals[0];
        int updateMinY = vals[1];
        int updateWidth = vals[2];
        int updateXStep = vals[4];
        int updateYStep = vals[5];

        int bitDepth = metadata.IHDR_bitDepth;
        int inputBands = inputBandsForColorType[metadata.IHDR_colorType];
        int bytesPerPixel = (bitDepth == 16) ? 2 : 1; 
        bytesPerPixel *= inputBands;
        
        int bytesPerRow = (inputBands*passWidth*bitDepth + 7)/8;
        int eltsPerRow = (bitDepth == 16) ? bytesPerRow/2 : bytesPerRow;

        // If no pixels need updating, just skip the input data 
        if (updateWidth == 0) {
            for (int srcY = 0; srcY < passHeight; srcY++) {
                // Update count of pixels read
                updateImageProgress(passWidth);
                // Skip filter byte and the remaining row bytes
                pixelStream.skipBytes(1 + bytesPerRow);
            }
            return;
        }
        
        // Backwards map from destination pixels
        // (dstX = updateMinX + k*updateXStep)
        // to source pixels (sourceX), and then
        // to offset and skip in passRow (srcX and srcXStep)  
        int sourceX = 
            (updateMinX - destinationOffset.x)*sourceXSubsampling +
            sourceRegion.x;
        int srcX = (sourceX - xStart)/xStep;
        
        // Compute the step factor in the source 
        int srcXStep = updateXStep*sourceXSubsampling/xStep;

        byte[] byteData = null;
        short[] shortData = null;
        byte[] curr = new byte[bytesPerRow];
        byte[] prior = new byte[bytesPerRow];

        // Create a 1-row tall Raster to hold the data
        WritableRaster passRow = createRaster(passWidth, 1, inputBands,
                                              eltsPerRow,
                                              bitDepth);
        
        // Create an array suitable for holding one pixel
        int[] ps = passRow.getPixel(0, 0, (int[])null);
        
        DataBuffer dataBuffer = passRow.getDataBuffer();
        int type = dataBuffer.getDataType();
        if (type == DataBuffer.TYPE_BYTE) {
            byteData = ((DataBufferByte)dataBuffer).getData();
        } else {
            shortData = ((DataBufferUShort)dataBuffer).getData();
        }
        
        processPassStarted(theImage,
                           passNum,
                           sourceMinProgressivePass,
                           sourceMaxProgressivePass,
                           updateMinX, updateMinY,
                           updateXStep, updateYStep,
                           destinationBands);
        
        // Handle source and destination bands
        if (sourceBands != null) {
            passRow = passRow.createWritableChild(0, 0,
                                                  passRow.getWidth(), 1,
                                                  0, 0,
                                                  sourceBands);
        }
        if (destinationBands != null) {
            imRas = imRas.createWritableChild(0, 0,
                                              imRas.getWidth(),
                                              imRas.getHeight(),
                                              0, 0,
                                              destinationBands);
        }

        // Determine if all of the relevant output bands have the
        // same bit depth as the source data
        boolean adjustBitDepths = false;
        int[] outputSampleSize = imRas.getSampleModel().getSampleSize();
        int numBands = outputSampleSize.length;
        for (int b = 0; b < numBands; b++) {
            if (outputSampleSize[b] != bitDepth) {
                adjustBitDepths = true;
                break;
            }
        }

        // If the bit depths differ, create a lookup table per band to perform
        // the conversion
        int[][] scale = null;
        if (adjustBitDepths) {
            int maxInSample = (1 << bitDepth) - 1;
            int halfMaxInSample = maxInSample/2;
            scale = new int[numBands][];
            for (int b = 0; b < numBands; b++) {
                int maxOutSample = (1 << outputSampleSize[b]) - 1;
                scale[b] = new int[maxInSample + 1];
                for (int s = 0; s <= maxInSample; s++) {
                    scale[b][s] =
                        (s*maxOutSample + halfMaxInSample)/maxInSample;
                }
            }
        }

        // Limit passRow to relevant area for the case where we
        // will can setRect to copy a contiguous span
        boolean useSetRect = srcXStep == 1 &&
            updateXStep == 1 &&
            !adjustBitDepths;
        if (useSetRect) {
            passRow = passRow.createWritableChild(srcX, 0,
                                                  updateWidth, 1, 
                                                  0, 0,
                                                  null);
        }

        // Decode the (sub)image row-by-row
        for (int srcY = 0; srcY < passHeight; srcY++) {
            // Update count of pixels read
            updateImageProgress(passWidth);
            
            // Read the filter type byte and a row of data
            int filter = pixelStream.read();
            try {
                // Swap curr and prior
                byte[] tmp = prior;
                prior = curr;
                curr = tmp;

                pixelStream.readFully(curr, 0, bytesPerRow);
            } catch (java.util.zip.ZipException ze) {
                // TODO - throw a more meaningful exception
                throw ze;
            }

            switch (filter) {
            case PNG_FILTER_NONE:
                break;
            case PNG_FILTER_SUB:
                decodeSubFilter(curr, 0, bytesPerRow, bytesPerPixel);
                break;
            case PNG_FILTER_UP:
                decodeUpFilter(curr, 0, prior, 0, bytesPerRow);
                break;
            case PNG_FILTER_AVERAGE:
                decodeAverageFilter(curr, 0, prior, 0, bytesPerRow,
                                    bytesPerPixel);
                break;
            case PNG_FILTER_PAETH:
                decodePaethFilter(curr, 0, prior, 0, bytesPerRow,
                                  bytesPerPixel);
                break;
            default:
                throw new IIOException("Unknown row filter type (= " +
                                       filter + ")!");
            }

            // Copy data into passRow byte by byte
            if (bitDepth < 16) {
                System.arraycopy(curr, 0, byteData, 0, bytesPerRow);
            } else {
                int idx = 0;
                for (int j = 0; j < eltsPerRow; j++) {
                    shortData[j] =
                        (short)((curr[idx] << 8) | (curr[idx + 1] & 0xff));
                    idx += 2;
                }
            }

            // True Y position in source
            int sourceY = srcY*yStep + yStart;
            if ((sourceY >= sourceRegion.y) && 
                (sourceY < sourceRegion.y + sourceRegion.height) &&
                (((sourceY - sourceRegion.y) %
                  sourceYSubsampling) == 0)) {
                
                int dstY = destinationOffset.y +
                    (sourceY - sourceRegion.y)/sourceYSubsampling;
                if (dstY < dstMinY) {
                    continue;
                }
                if (dstY > dstMaxY) {
                    break;
                }

                if (useSetRect) {