Split SkBmpCodec into three separate classes

src/codec/SkBmpStandardCodec.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 "SkBmpStandardCodec.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())) {
+        // In order to correct invalid transparent decodes, we will always
+        // allow dst alpha type to be opaque.
+        if (kOpaque_SkAlphaType != dst.alphaType()) {
+            return false;
+        }
+        SkCodecPrintf("Warning: The client should not request an opaque "

[scroggo, 2015/08/04 16:16:47]

Oh, wait, so we are allowing this only because we'll call it in this mode?

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

Yes.  Maybe there is a better way to bypass this check?

+                "decode if we indicate that the encoded data is not opaque. "
+                "We should only hit this case on the automatic correction "
+                "of invalid transparent decodes.\n");
+    }
+
+    // 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
+ */
+SkBmpStandardCodec::SkBmpStandardCodec(const SkImageInfo& info, SkStream* stream,
+                                       uint16_t bitsPerPixel, uint32_t numColors,
+                                       uint32_t bytesPerColor, uint32_t offset,
+                                       SkBmpCodec::RowOrder rowOrder, bool isIco)
+    : INHERITED(info, stream, bitsPerPixel, rowOrder)
+    , fColorTable(NULL)
+    , fNumColors(numColors)
+    , fBytesPerColor(bytesPerColor)
+    , fOffset(offset)
+    , fSwizzler(NULL)
+    , fSrcBuffer(NULL)
+    , fIsIco(isIco)
+    , fIsTransparent(true)
+{}
+
+/*
+ * Initiates the bitmap decode
+ */
+SkCodec::Result SkBmpStandardCodec::onGetPixels(const SkImageInfo& dstInfo,
+                                        void* dst, size_t dstRowBytes,
+                                        const Options& opts,
+                                        SkPMColor* inputColorPtr,
+                                        int* inputColorCount) {
+    if (!this->handleRewind(fIsIco)) {
+        SkCodecPrintf("Error: could not rewind image stream.\n");
+        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->initializeSwizzler(dstInfo, opts)) {
+        SkCodecPrintf("Error: cannot initialize swizzler.\n");
+        return kInvalidConversion;
+    }
+
+    // Perform the decode
+    SkCodec::Result result = decode(dstInfo, dst, dstRowBytes, opts);
+
+    // Fix the decode, if neceessary
+    if (fIsTransparent) {
+        result = SkBmpCodec::FixTransparentDecode(dst, dstRowBytes,
+                inputColorPtr, inputColorCount, this->stream()->duplicate());
+    }
+
+    return result;
+}
+
+/*
+ * Process the color table for the bmp input
+ */
+ bool SkBmpStandardCodec::createColorTable(SkAlphaType alphaType, int* numColors) {

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

IIUC, there are now two versions of createColorTable? Can they share code (I
haven't looked through them to see how similar they are)?

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

I made a comment about this in the old upload.  I didn't want to share them
because of differences with regard to alpha and inIco and because they both
depend on a lot of fields.  These are fields that they share, but SkBmpCodec
does not have access to these fields because SkBmpMaskCodec does not share them.
 I guess we could subclass SkBmpCodec with SkBmpMightHaveColorTableCodec and
then subclass that with Standard and RLE, but IMO sharing this code is more
trouble than it's worth.

+    // 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;
+        }
+
+        // Choose the proper packing function
+        SkPMColor (*packARGB) (uint32_t, uint32_t, uint32_t, uint32_t);
+        switch (alphaType) {
+            case kOpaque_SkAlphaType:
+            case kUnpremul_SkAlphaType:
+                packARGB = &SkPackARGB32NoCheck;
+                break;
+            case kPremul_SkAlphaType:
+                packARGB = &SkPreMultiplyARGB;
+                break;
+            default:
+                // This should not be reached because conversion possible
+                // should fail if the alpha type is not one of the above
+                // values.
+                SkASSERT(false);
+                packARGB = NULL;
+                break;
+        }
+
+        // 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);
+            uint8_t alpha;
+            if (kOpaque_SkAlphaType == alphaType) {
+                alpha = 0xFF;
+            } else {
+                alpha = get_byte(cBuffer.get(), i*fBytesPerColor + 3);
+            }
+            colorTable[i] = packARGB(alpha, 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)));
+    }
+
+    // Bmp-in-Ico files do not use an offset to indicate where the pixel data
+    // begins.  Pixel data always begins immediately after the color table.
+    if (!fIsIco) {
+        // 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;
+}
+
+static const SkPMColor* get_color_ptr(SkColorTable* colorTable) {
+    return NULL != colorTable ? colorTable->readColors() : NULL;
+}
+
+bool SkBmpStandardCodec::initializeSwizzler(const SkImageInfo& dstInfo,
+                                            const Options& opts) {
+    // Allocate space for a row buffer
+    const size_t rowBytes = SkAlign4(compute_row_bytes(dstInfo.width(), this->bitsPerPixel()));
+    fSrcBuffer.reset(SkNEW_ARRAY(uint8_t, rowBytes));
+
+    // Get swizzler configuration
+    SkSwizzler::SrcConfig config;
+    switch (this->bitsPerPixel()) {
+        case 1:
+            config = SkSwizzler::kIndex1;
+            break;
+        case 2:
+            config = SkSwizzler::kIndex2;
+            break;
+        case 4:
+            config = SkSwizzler::kIndex4;
+            break;
+        case 8:
+            config = SkSwizzler::kIndex;
+            break;
+        case 24:
+            config = SkSwizzler::kBGR;
+            break;
+        case 32:
+            if (kOpaque_SkAlphaType == dstInfo.alphaType()) {
+                config = SkSwizzler::kBGRX;
+            } else {
+                config = SkSwizzler::kBGRA;
+            }
+            break;
+        default:
+            SkASSERT(false);
+            return kInvalidInput;
+    }
+
+    // Get a pointer to the color table if it exists
+    const SkPMColor* colorPtr = get_color_ptr(fColorTable.get());
+
+    // Create swizzler
+    fSwizzler.reset(SkSwizzler::CreateSwizzler(config,
+            colorPtr, dstInfo, opts.fZeroInitialized));
+
+    if (NULL == fSwizzler.get()) {
+        return false;
+    }
+    return true;
+}
+
+/*
+ * Choose a fill for failures due to an incomplete image.  We will use zero as
+ * the default palette index, black for opaque images, and transparent for
+ * non-opaque images.
+ */
+static uint32_t get_fill_color_or_index(uint16_t bitsPerPixels, SkAlphaType alphaType) {
+    uint32_t fillColorOrIndex;
+    switch (bitsPerPixels) {
+        case 1:
+        case 2:
+        case 4:
+        case 8:
+            fillColorOrIndex = 0;
+            break;
+        case 24:
+            fillColorOrIndex = SK_ColorBLACK;
+            break;
+        case 32:
+            if (kOpaque_SkAlphaType == alphaType) {
+                fillColorOrIndex = SK_ColorBLACK;
+            } else {
+                fillColorOrIndex = SK_ColorTRANSPARENT;
+            }
+            break;
+        default:
+            SkASSERT(false);
+            return 0;
+    }
+    return fillColorOrIndex;
+}
+
+/*
+ * Performs the bitmap decoding for standard input format
+ */
+SkCodec::Result SkBmpStandardCodec::decode(const SkImageInfo& dstInfo,
+                                   void* dst, size_t dstRowBytes,
+                                   const Options& opts) {
+    // Set constant values
+    const int width = dstInfo.width();
+    const int height = dstInfo.height();
+    const size_t rowBytes = SkAlign4(compute_row_bytes(width, this->bitsPerPixel()));
+
+    // Iterate over rows of the image
+    for (int y = 0; y < height; y++) {
+        // Read a row of the input
+        if (this->stream()->read(fSrcBuffer.get(), rowBytes) != rowBytes) {
+            SkCodecPrintf("Warning: incomplete input stream.\n");
+            // Fill the destination image on failure
+            // Get the fill color/index and check if it is 0
+            uint32_t fillColorOrIndex = get_fill_color_or_index(this->bitsPerPixel(),
+                    dstInfo.alphaType());
+            bool zeroFill = (0 == fillColorOrIndex);
+
+            if (kNo_ZeroInitialized == opts.fZeroInitialized || !zeroFill) {
+                // Get a pointer to the color table if it exists
+                const SkPMColor* colorPtr = get_color_ptr(fColorTable.get());
+
+                void* dstStart = this->getDstStartRow(dst, dstRowBytes, y);
+                SkSwizzler::Fill(dstStart, dstInfo, dstRowBytes, dstInfo.height() - y,
+                        fillColorOrIndex, colorPtr);
+            }
+            return kIncompleteInput;
+        }
+
+        // Decode the row in destination format
+        uint32_t row;
+        if (SkBmpCodec::kTopDown_RowOrder == this->rowOrder()) {
+            row = y;
+        } else {
+            row = height - 1 - y;
+        }
+
+        void* dstRow = SkTAddOffset<void>(dst, row * dstRowBytes);
+        SkSwizzler::ResultAlpha r = fSwizzler->swizzle(dstRow, fSrcBuffer.get());
+        fIsTransparent &= SkSwizzler::IsTransparent(r);
+    }
+
+    // Finally, apply the AND mask for bmp-in-ico images
+    if (fIsIco) {
+        // The AND mask is always 1 bit per pixel
+        const size_t rowBytes = SkAlign4(compute_row_bytes(width, 1));
+
+        SkPMColor* dstPtr = (SkPMColor*) dst;
+        for (int y = 0; y < height; y++) {
+            // The srcBuffer will at least be large enough
+            if (stream()->read(fSrcBuffer.get(), rowBytes) != rowBytes) {
+                SkCodecPrintf("Warning: incomplete AND mask for bmp-in-ico.\n");
+                return kIncompleteInput;
+            }
+
+            int row;
+            if (SkBmpCodec::kBottomUp_RowOrder == this->rowOrder()) {
+                row = height - y - 1;
+            } else {
+                row = y;
+            }
+
+            SkPMColor* dstRow =
+                    SkTAddOffset<SkPMColor>(dstPtr, row * dstRowBytes);
+
+            for (int x = 0; x < width; x++) {
+                int quotient;
+                int modulus;
+                SkTDivMod(x, 8, &quotient, &modulus);
+                uint32_t shift = 7 - modulus;
+                uint32_t alphaBit =
+                        (fSrcBuffer.get()[quotient] >> shift) & 0x1;
+                dstRow[x] &= alphaBit - 1;
+            }
+        }
+    }
+
+    // Finished decoding the entire image
+    return kSuccess;
+}