pngimagereader.java

java jdk 1.4的源码

            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;
        byte[] curr = new byte[bytesPerRow];

        // Read the image row-by-row
        for (int srcY = 0; srcY < passHeight; srcY++) {
            // Read the filter type byte and a row of data
            int filter = pixelStream.read();
            pixelStream.readFully(curr, 0, bytesPerRow);

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

    // Helper for protected computeUpdatedPixels method
    private static void computeUpdatedPixels(int sourceOffset,
                                             int sourceExtent,
                                             int destinationOffset,
                                             int dstMin,
                                             int dstMax,
                                             int sourceSubsampling,
                                             int passStart,
                                             int passExtent,
                                             int passPeriod,
                                             int[] vals,
                                             int offset) {

        // We need to satisfy the congruences:
        // dst = destinationOffset + (src - sourceOffset)/sourceSubsampling
        //
        // src - passStart == 0 (mod passPeriod)
        // src - sourceOffset == 0 (mod sourceSubsampling)
        //
        // subject to the inequalities:
        //
        // src >= passStart
        // src < passStart + passExtent
        // src >= sourceOffset
        // src < sourceOffset + sourceExtent
        // dst >= dstMin
        // dst <= dstmax
        //
        // where
        //
        // dst = destinationOffset + (src - sourceOffset)/sourceSubsampling
        //
        // For now we use a brute-force approach although we could
        // attempt to analyze the congruences.  If passPeriod and
        // sourceSubsamling are relatively prime, the period will be
        // their product.  If they share a common factor, either the
        // period will be equal to the larger value, or the sequences
        // will be completely disjoint, depending on the relationship
        // between passStart and sourceOffset.  Since we only have to do this
        // twice per image (once each for X and Y), it seems cheap enough
        // to do it the straightforward way.

        boolean gotPixel = false;
        int firstDst = -1;
        int secondDst = -1;
        int lastDst = -1;

        for (int i = 0; i < passExtent; i++) {
            int src = passStart + i*passPeriod;
            if (src < sourceOffset) {
                continue;
            }
            if ((src - sourceOffset) % sourceSubsampling != 0) {
                continue;
            }
            if (src >= sourceOffset + sourceExtent) {
                break;
            }

            int dst = destinationOffset +
                (src - sourceOffset)/sourceSubsampling;
            if (dst < dstMin) {
                continue;
            }
            if (dst > dstMax) {
                break;
            }

            if (!gotPixel) {
                firstDst = dst; // Record smallest valid pixel
                gotPixel = true;
            } else if (secondDst == -1) {
                secondDst = dst; // Record second smallest valid pixel
            }
            lastDst = dst; // Record largest valid pixel
        }

        vals[offset] = firstDst;

        // If we never saw a valid pixel, set width to 0
        if (!gotPixel) {
            vals[offset + 2] = 0;
        } else {
            vals[offset + 2] = lastDst - firstDst + 1;
        }

        // The period is given by the difference of any two adjacent pixels
        vals[offset + 4] = Math.max(secondDst - firstDst, 1);
    }

    /**
     * A utility method that computes the exact set of destination
     * pixels that will be written during a particular decoding pass.
     * The intent is to simplify the work done by readers in combining
     * the source region, source subsampling, and destination offset
     * information obtained from the <code>ImageReadParam</code> with
     * the offsets and periods of a progressive or interlaced decoding
     * pass.
     *
     * @param sourceRegion a <code>Rectangle</code> containing the
     * source region being read, offset by the source subsampling
     * offsets, and clipped against the source bounds, as returned by
     * the <code>getSourceRegion</code> method.
     * @param destinationOffset a <code>Point</code> containing the
     * coordinates of the upper-left pixel to be written in the
     * destination.
     * @param dstMinX the smallest X coordinate (inclusive) of the
     * destination <code>Raster</code>.
     * @param dstMinY the smallest Y coordinate (inclusive) of the
     * destination <code>Raster</code>.
     * @param dstMaxX the largest X coordinate (inclusive) of the destination
     * <code>Raster</code>.
     * @param dstMaxY the largest Y coordinate (inclusive) of the destination
     * <code>Raster</code>.
     * @param sourceXSubsampling the X subsampling factor.
     * @param sourceYSubsampling the Y subsampling factor.
     * @param passXStart the smallest source X coordinate (inclusive)
     * of the current progressive pass.
     * @param passYStart the smallest source Y coordinate (inclusive)
     * of the current progressive pass.
     * @param passWidth the width in pixels of the current progressive
     * pass.
     * @param passHeight the height in pixels of the current progressive
     * pass.
     * @param passPeriodX the X period (horizontal spacing between
     * pixels) of the current progressive pass.
     * @param passPeriodY the Y period (vertical spacing between
     * pixels) of the current progressive pass.
     *
     * @return an array of 6 <code>int</code>s containing the
     * destination min X, min Y, width, height, X period and Y period
     * of the region that will be updated.
     */
    private static int[] computeUpdatedPixels(Rectangle sourceRegion,
                                              Point destinationOffset,
                                              int dstMinX,
                                              int dstMinY,
                                              int dstMaxX,
                                              int dstMaxY,
                                              int sourceXSubsampling,
                                              int sourceYSubsampling,
                                              int passXStart,
                                              int passYStart,
                                              int passWidth,
                                              int passHeight,
                                              int passPeriodX,
                                              int passPeriodY) {
        int[] vals = new int[6];
        computeUpdatedPixels(sourceRegion.x, sourceRegion.width,
                             destinationOffset.x,
                             dstMinX, dstMaxX, sourceXSubsampling,
                             passXStart, passWidth, passPeriodX,
                             vals, 0);
        computeUpdatedPixels(sourceRegion.y, sourceRegion.height,
                             destinationOffset.y,
                             dstMinY, dstMaxY, sourceYSubsampling,
                             passYStart, passHeight, passPeriodY,
                             vals, 1);
        return vals;
    }

    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 = 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);
                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