Split SkBmpCodec into three separate classes

src/codec/SkBmpRLECodec.cpp

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkBmpRLECodec.h"
+#include "SkCodecPriv.h"
+#include "SkColorPriv.h"
+#include "SkScanlineDecoder.h"
+#include "SkStream.h"
+
+/*
+ * Checks if the conversion between the input image and the requested output
+ * image has been implemented
+ */
+static bool conversion_possible(const SkImageInfo& dst,
+                                const SkImageInfo& src) {
+    // Ensure that the profile type is unchanged
+    if (dst.profileType() != src.profileType()) {
+        return false;
+    }
+
+    // Ensure the alpha type is valid
+    if (!valid_alpha(dst.alphaType(), src.alphaType())) {
+        return false;
+    }
+
+    // Check for supported color types
+    switch (dst.colorType()) {
+        // Allow output to kN32 from any type of input
+        case kN32_SkColorType:
+            return true;
+        // Allow output to kIndex_8 from compatible inputs
+        case kIndex_8_SkColorType:
+            return kIndex_8_SkColorType == src.colorType();
+        default:
+            return false;
+    }
+}
+
+/*
+ * Creates an instance of the decoder
+ * Called only by NewFromStream
+ */
+SkBmpRLECodec::SkBmpRLECodec(const SkImageInfo& info, SkStream* stream,
+                             uint16_t bitsPerPixel, uint32_t numColors,
+                             uint32_t bytesPerColor, uint32_t offset,
+                             SkBmpCodec::RowOrder rowOrder, size_t RLEBytes)
+    : INHERITED(info, stream, bitsPerPixel, rowOrder)
+    , fColorTable(NULL)
+    , fNumColors(numColors)
+    , fBytesPerColor(bytesPerColor)
+    , fOffset(offset)
+    , fStreamBuffer(SkNEW_ARRAY(uint8_t, RLEBytes))
+    , fRLEBytes(RLEBytes)
+    , fCurrRLEByte(0)
+{}
+
+/*
+ * Initiates the bitmap decode
+ */
+SkCodec::Result SkBmpRLECodec::onGetPixels(const SkImageInfo& dstInfo,
+                                        void* dst, size_t dstRowBytes,
+                                        const Options& opts,
+                                        SkPMColor* inputColorPtr,
+                                        int* inputColorCount) {
+    if (!this->handleRewind(false)) {
+        SkCodecPrintf("Error: could not rewind image stream.\n");

[scroggo, 2015/08/04 16:16:46]

Do you think this is necessary? It seems like returning kCouldNotRewind tells
the caller this. I'm not opposed to it, just curious.

[msarett, 2015/08/04 23:14:45]

Not necessary

+        return kCouldNotRewind;
+    }
+    if (opts.fSubset) {
+        // Subsets are not supported.
+        return kUnimplemented;
+    }
+    if (dstInfo.dimensions() != this->getInfo().dimensions()) {
+        SkCodecPrintf("Error: scaling not supported.\n");
+        return kInvalidScale;
+    }
+    if (!conversion_possible(dstInfo, this->getInfo())) {
+        SkCodecPrintf("Error: cannot convert input type to output type.\n");
+        return kInvalidConversion;
+    }
+
+    // Create the color table if necessary and prepare the stream for decode
+    // Note that if it is non-NULL, inputColorCount will be modified
+    if (!this->createColorTable(dstInfo.alphaType(), inputColorCount)) {
+        SkCodecPrintf("Error: could not create color table.\n");
+        return kInvalidInput;
+    }
+
+    // Copy the color table to the client if necessary
+    copy_color_table(dstInfo, fColorTable, inputColorPtr, inputColorCount);
+
+    // Initialize a swizzler if necessary
+    if (!this->initializeStreamBuffer()) {
+        SkCodecPrintf("Error: cannot initialize swizzler.\n");
+        return kInvalidConversion;
+    }
+
+    // Perform the decode
+    return decode(dstInfo, dst, dstRowBytes, opts);
+}
+
+/*
+ * Process the color table for the bmp input
+ */
+ bool SkBmpRLECodec::createColorTable(SkAlphaType alphaType, int* numColors) {
+    // Allocate memory for color table
+    uint32_t colorBytes = 0;
+    uint32_t maxColors = 0;
+    SkPMColor colorTable[256];
+    if (this->bitsPerPixel() <= 8) {
+        // Zero is a default for maxColors
+        // Also set fNumColors to maxColors when it is too large
+        maxColors = 1 << this->bitsPerPixel();
+        if (fNumColors == 0 || fNumColors >= maxColors) {
+            fNumColors = maxColors;
+        }
+
+        // Inform the caller of the number of colors
+        if (NULL != numColors) {
+            // We set the number of colors to maxColors in order to ensure
+            // safe memory accesses.  Otherwise, an invalid pixel could
+            // access memory outside of our color table array.
+            *numColors = maxColors;
+        }
+
+        // Read the color table from the stream
+        colorBytes = fNumColors * fBytesPerColor;
+        SkAutoTDeleteArray<uint8_t> cBuffer(SkNEW_ARRAY(uint8_t, colorBytes));
+        if (stream()->read(cBuffer.get(), colorBytes) != colorBytes) {
+            SkCodecPrintf("Error: unable to read color table.\n");
+            return false;
+        }
+
+        // Fill in the color table
+        uint32_t i = 0;
+        for (; i < fNumColors; i++) {
+            uint8_t blue = get_byte(cBuffer.get(), i*fBytesPerColor);
+            uint8_t green = get_byte(cBuffer.get(), i*fBytesPerColor + 1);
+            uint8_t red = get_byte(cBuffer.get(), i*fBytesPerColor + 2);
+            colorTable[i] = SkPackARGB32NoCheck(0xFF, red, green, blue);
+        }
+
+        // To avoid segmentation faults on bad pixel data, fill the end of the
+        // color table with black.  This is the same the behavior as the
+        // chromium decoder.
+        for (; i < maxColors; i++) {
+            colorTable[i] = SkPackARGB32NoCheck(0xFF, 0, 0, 0);
+        }
+
+        // Set the color table
+        fColorTable.reset(SkNEW_ARGS(SkColorTable, (colorTable, maxColors)));
+    }
+
+    // Check that we have not read past the pixel array offset
+    if(fOffset < colorBytes) {
+        // This may occur on OS 2.1 and other old versions where the color
+        // table defaults to max size, and the bmp tries to use a smaller
+        // color table.  This is invalid, and our decision is to indicate
+        // an error, rather than try to guess the intended size of the
+        // color table.
+        SkCodecPrintf("Error: pixel data offset less than color table size.\n");
+        return false;
+    }
+
+    // After reading the color table, skip to the start of the pixel array
+    if (stream()->skip(fOffset - colorBytes) != fOffset - colorBytes) {
+        SkCodecPrintf("Error: unable to skip to image data.\n");
+        return false;
+    }
+
+    // Return true on success
+    return true;
+}
+
+bool SkBmpRLECodec::initializeStreamBuffer() {
+    // Setup a buffer to contain the full input stream
+    size_t totalBytes = this->stream()->read(fStreamBuffer.get(), fRLEBytes);
+    if (totalBytes < fRLEBytes) {
+        fRLEBytes = totalBytes;
+        SkCodecPrintf("Warning: incomplete RLE file.\n");
+    }
+    if (fRLEBytes == 0) {
+        SkCodecPrintf("Error: could not read RLE image data.\n");
+        return false;
+    }
+    return true;
+}
+
+/*
+ * Set an RLE pixel using the color table
+ */
+void SkBmpRLECodec::setPixel(void* dst, size_t dstRowBytes,
+                             const SkImageInfo& dstInfo, uint32_t x, uint32_t y,
+                             uint8_t index) {
+    // Set the row
+    int height = dstInfo.height();
+    int row;
+    if (SkBmpCodec::kBottomUp_RowOrder == this->rowOrder()) {
+        row = height - y - 1;
+    } else {
+        row = y;
+    }
+
+    // Set the pixel based on destination color type
+    switch (dstInfo.colorType()) {
+        case kN32_SkColorType: {
+            SkPMColor* dstRow = SkTAddOffset<SkPMColor>((SkPMColor*) dst,
+                    row * (int) dstRowBytes);
+            dstRow[x] = fColorTable->operator[](index);
+            break;
+        }
+        default:
+            // This case should not be reached.  We should catch an invalid
+            // color type when we check that the conversion is possible.
+            SkASSERT(false);
+            break;
+    }
+}
+
+/*
+ * Set an RLE pixel from R, G, B values
+ */
+void SkBmpRLECodec::setRGBPixel(void* dst, size_t dstRowBytes,
+                                const SkImageInfo& dstInfo, uint32_t x,
+                                uint32_t y, uint8_t red, uint8_t green,
+                                uint8_t blue) {
+    // Set the row
+    int height = dstInfo.height();
+    int row;
+    if (SkBmpCodec::kBottomUp_RowOrder == this->rowOrder()) {
+        row = height - y - 1;
+    } else {
+        row = y;
+    }
+
+    // Set the pixel based on destination color type
+    switch (dstInfo.colorType()) {
+        case kN32_SkColorType: {
+            SkPMColor* dstRow = SkTAddOffset<SkPMColor>((SkPMColor*) dst,
+                    row * (int) dstRowBytes);
+            dstRow[x] = SkPackARGB32NoCheck(0xFF, red, green, blue);
+            break;
+        }
+        default:
+            // This case should not be reached.  We should catch an invalid
+            // color type when we check that the conversion is possible.
+            SkASSERT(false);
+            break;
+    }
+}
+
+/*
+ * Performs the bitmap decoding for RLE input format
+ * RLE decoding is performed all at once, rather than a one row at a time
+ */
+SkCodec::Result SkBmpRLECodec::decode(const SkImageInfo& dstInfo,
+                                      void* dst, size_t dstRowBytes,
+                                      const Options& opts) {
+    // Set RLE flags
+    static const uint8_t RLE_ESCAPE = 0;
+    static const uint8_t RLE_EOL = 0;
+    static const uint8_t RLE_EOF = 1;
+    static const uint8_t RLE_DELTA = 2;
+
+    // Set constant values
+    const int width = dstInfo.width();
+    const int height = dstInfo.height();
+
+    // Destination parameters
+    int x = 0;
+    int y = 0;
+
+    // Set the background as transparent.  Then, if the RLE code skips pixels,
+    // the skipped pixels will be transparent.
+    // Because of the need for transparent pixels, kN32 is the only color
+    // type that makes sense for the destination format.
+    SkASSERT(kN32_SkColorType == dstInfo.colorType());
+    if (kNo_ZeroInitialized == opts.fZeroInitialized) {
+        SkSwizzler::Fill(dst, dstInfo, dstRowBytes, height, SK_ColorTRANSPARENT, NULL);
+    }
+
+    while (true) {
+        // If we have reached a row that is beyond the requested height, we have
+        // succeeded.
+        if (y >= height) {
+            // It would be better to check for the EOF marker before returning
+            // success, but we may be performing a scanline decode, which
+            // may require us to stop before decoding the full height.
+            return kSuccess;
+        }
+
+        // Every entry takes at least two bytes
+        if ((int) fRLEBytes - fCurrRLEByte < 2) {
+            SkCodecPrintf("Warning: incomplete RLE input.\n");
+            return kIncompleteInput;
+        }
+
+        // Read the next two bytes.  These bytes have different meanings
+        // depending on their values.  In the first interpretation, the first
+        // byte is an escape flag and the second byte indicates what special
+        // task to perform.
+        const uint8_t flag = fStreamBuffer.get()[fCurrRLEByte++];
+        const uint8_t task = fStreamBuffer.get()[fCurrRLEByte++];
+
+        // Perform decoding
+        if (RLE_ESCAPE == flag) {
+            switch (task) {
+                case RLE_EOL:
+                    x = 0;
+                    y++;
+                    break;
+                case RLE_EOF:
+                    return kSuccess;
+                case RLE_DELTA: {
+                    // Two bytes are needed to specify delta
+                    if ((int) fRLEBytes - fCurrRLEByte < 2) {
+                        SkCodecPrintf("Warning: incomplete RLE input\n");
+                        return kIncompleteInput;
+                    }
+                    // Modify x and y
+                    const uint8_t dx = fStreamBuffer.get()[fCurrRLEByte++];
+                    const uint8_t dy = fStreamBuffer.get()[fCurrRLEByte++];
+                    x += dx;
+                    y += dy;
+                    if (x > width || y > height) {
+                        SkCodecPrintf("Warning: invalid RLE input 1.\n");
+                        return kIncompleteInput;
+                    }
+                    break;
+                }
+                default: {
+                    // If task does not match any of the above signals, it
+                    // indicates that we have a sequence of non-RLE pixels.
+                    // Furthermore, the value of task is equal to the number
+                    // of pixels to interpret.
+                    uint8_t numPixels = task;
+                    const size_t rowBytes = compute_row_bytes(numPixels,
+                            this->bitsPerPixel());
+                    // Abort if setting numPixels moves us off the edge of the
+                    // image.  Also abort if there are not enough bytes
+                    // remaining in the stream to set numPixels.
+                    if (x + numPixels > width ||
+                            (int) fRLEBytes - fCurrRLEByte < SkAlign2(rowBytes)) {
+                        SkCodecPrintf("Warning: invalid RLE input 2.\n");
+                        return kIncompleteInput;
+                    }
+                    // Set numPixels number of pixels
+                    while (numPixels > 0) {
+                        switch(this->bitsPerPixel()) {
+                            case 4: {
+                                SkASSERT(fCurrRLEByte < fRLEBytes);
+                                uint8_t val = fStreamBuffer.get()[fCurrRLEByte++];
+                                setPixel(dst, dstRowBytes, dstInfo, x++,
+                                        y, val >> 4);
+                                numPixels--;
+                                if (numPixels != 0) {
+                                    setPixel(dst, dstRowBytes, dstInfo,
+                                            x++, y, val & 0xF);
+                                    numPixels--;
+                                }
+                                break;
+                            }
+                            case 8:
+                                SkASSERT(fCurrRLEByte < fRLEBytes);
+                                setPixel(dst, dstRowBytes, dstInfo, x++,
+                                        y, fStreamBuffer.get()[fCurrRLEByte++]);
+                                numPixels--;
+                                break;
+                            case 24: {
+                                SkASSERT(fCurrRLEByte + 2 < fRLEBytes);
+                                uint8_t blue = fStreamBuffer.get()[fCurrRLEByte++];
+                                uint8_t green = fStreamBuffer.get()[fCurrRLEByte++];
+                                uint8_t red = fStreamBuffer.get()[fCurrRLEByte++];
+                                setRGBPixel(dst, dstRowBytes, dstInfo,
+                                            x++, y, red, green, blue);
+                                numPixels--;
+                            }
+                            default:
+                                SkASSERT(false);
+                                return kInvalidInput;
+                        }
+                    }
+                    // Skip a byte if necessary to maintain alignment
+                    if (!SkIsAlign2(rowBytes)) {
+                        fCurrRLEByte++;
+                    }
+                    break;
+                }
+            }
+        } else {
+            // If the first byte read is not a flag, it indicates the number of
+            // pixels to set in RLE mode.
+            const uint8_t numPixels = flag;
+            const int endX = SkTMin<int>(x + numPixels, width);
+
+            if (24 == this->bitsPerPixel()) {
+                // In RLE24, the second byte read is part of the pixel color.
+                // There are two more required bytes to finish encoding the
+                // color.
+                if ((int) fRLEBytes - fCurrRLEByte < 2) {
+                    SkCodecPrintf("Warning: incomplete RLE input\n");
+                    return kIncompleteInput;
+                }
+
+                // Fill the pixels up to endX with the specified color
+                uint8_t blue = task;
+                uint8_t green = fStreamBuffer.get()[fCurrRLEByte++];
+                uint8_t red = fStreamBuffer.get()[fCurrRLEByte++];
+                while (x < endX) {
+                    setRGBPixel(dst, dstRowBytes, dstInfo, x++, y, red,
+                            green, blue);
+                }
+            } else {
+                // In RLE8 or RLE4, the second byte read gives the index in the
+                // color table to look up the pixel color.
+                // RLE8 has one color index that gets repeated
+                // RLE4 has two color indexes in the upper and lower 4 bits of
+                // the bytes, which are alternated
+                uint8_t indices[2] = { task, task };
+                if (4 == this->bitsPerPixel()) {
+                    indices[0] >>= 4;
+                    indices[1] &= 0xf;
+                }
+
+                // Set the indicated number of pixels
+                for (int which = 0; x < endX; x++) {
+                    setPixel(dst, dstRowBytes, dstInfo, x, y,
+                            indices[which]);
+                    which = !which;
+                }
+            }
+        }
+    }
+}