Scanline decoding for bmp

src/codec/SkBmpCodec.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 "SkBmpCodec.h"
 #include "SkBmpMaskCodec.h"
 #include "SkBmpRLECodec.h"
@@ skipping 26 matching lines @@
     kBitMasks_BmpCompressionMethod =      3,
     kJpeg_BmpCompressionMethod =          4,
     kPng_BmpCompressionMethod =           5,
     kAlphaBitMasks_BmpCompressionMethod = 6,
     kCMYK_BmpCompressionMethod =          11,
     kCMYK8BitRLE_BmpCompressionMethod =   12,
     kCMYK4BitRLE_BmpCompressionMethod =   13
 };
 
 /*
- * Used to define the input format of the bmp
- */
-enum BmpInputFormat {
-    kStandard_BmpInputFormat,
-    kRLE_BmpInputFormat,
-    kBitMask_BmpInputFormat,
-    kUnknown_BmpInputFormat
-};
-
-/*
  * Checks the start of the stream to see if the image is a bitmap
  */
 bool SkBmpCodec::IsBmp(SkStream* stream) {
     // TODO: Support "IC", "PT", "CI", "CP", "BA"
     const char bmpSig[] = { 'B', 'M' };
     char buffer[sizeof(bmpSig)];
     return stream->read(buffer, sizeof(bmpSig)) == sizeof(bmpSig) &&
             !memcmp(buffer, bmpSig, sizeof(bmpSig));
 }
 
@@ skipping 398 matching lines @@
 
     if (codecOut) {
         // Set the image info
         const SkImageInfo& imageInfo = SkImageInfo::Make(width, height,
                 colorType, alphaType);
 
         // Return the codec
         switch (inputFormat) {
             case kStandard_BmpInputFormat:
                 *codecOut = SkNEW_ARGS(SkBmpStandardCodec, (imageInfo, stream,
-                        bitsPerPixel, numColors, bytesPerColor,
+                        inputFormat, bitsPerPixel, numColors, bytesPerColor,
                         offset - bytesRead, rowOrder, inIco));
                 return true;
             case kBitMask_BmpInputFormat:
                 // Bmp-in-Ico must be standard mode
                 if (inIco) {
                     SkCodecPrintf("Error: Icos may not use bit mask format.\n");
                     return false;
                 }
                 // Skip to the start of the pixel array.
                 // We can do this here because there is no color table to read
                 // in bit mask mode.
                 if (stream->skip(offset - bytesRead) != offset - bytesRead) {
                     SkCodecPrintf("Error: unable to skip to image data.\n");
                     return false;
                 }
 
                 *codecOut = SkNEW_ARGS(SkBmpMaskCodec, (imageInfo, stream,
-                        bitsPerPixel, masks.detach(), rowOrder));
+                        inputFormat, bitsPerPixel, masks.detach(), rowOrder));
                 return true;
             case kRLE_BmpInputFormat:
                 // Bmp-in-Ico must be standard mode
                 // When inIco is true, this line cannot be reached, since we
                 // require that RLE Bmps have a valid number of totalBytes, and
                 // Icos skip the header that contains totalBytes.
                 SkASSERT(!inIco);
                 *codecOut = SkNEW_ARGS(SkBmpRLECodec, (
-                        imageInfo, stream, bitsPerPixel, numColors,
+                        imageInfo, stream, inputFormat, bitsPerPixel, numColors,
                         bytesPerColor, offset - bytesRead, rowOrder, RLEBytes));
                 return true;
             default:
                 SkASSERT(false);
                 return false;
         }
     }
 
     return true;
 }
 
 /*
  * Creates a bmp decoder
  * Reads enough of the stream to determine the image format
  */
 SkCodec* SkBmpCodec::NewFromStream(SkStream* stream, bool inIco) {
     SkAutoTDelete<SkStream> streamDeleter(stream);
     SkCodec* codec = NULL;
     if (ReadHeader(stream, inIco, &codec)) {
         // codec has taken ownership of stream, so we do not need to
         // delete it.
         SkASSERT(codec);
         streamDeleter.detach();
         return codec;
     }
     return NULL;
 }
 
 SkBmpCodec::SkBmpCodec(const SkImageInfo& info, SkStream* stream,
-        uint16_t bitsPerPixel, RowOrder rowOrder)
+        BmpInputFormat inputFormat, uint16_t bitsPerPixel, RowOrder rowOrder)
     : INHERITED(info, stream)
+    , fInputFormat(inputFormat)
     , fBitsPerPixel(bitsPerPixel)
     , fRowOrder(rowOrder)
 {}
 
 bool SkBmpCodec::onRewind() {
     return SkBmpCodec::ReadHeader(this->stream(), this->inIco(), NULL);
 }
 
 /*
  * Get the destination row to start filling from
@@ skipping 11 matching lines @@
  */
 uint32_t SkBmpCodec::computeNumColors(uint32_t numColors) {
     // Zero is a default for maxColors
     // Also set numColors to maxColors when it is too large
     uint32_t maxColors = 1 << fBitsPerPixel;
     if (numColors == 0 || numColors >= maxColors) {
         return maxColors;
     }
     return numColors;
 }
+
+/*
+ * Scanline decoder for bmps
+ */
+class SkBmpScanlineDecoder : public SkScanlineDecoder {
+public:
+    SkBmpScanlineDecoder(SkBmpCodec* codec)
+        : INHERITED(codec->getInfo())
+        , fCodec(codec)
+    {}
+
+    SkCodec::Result onStart(const SkImageInfo& dstInfo, const SkCodec::Options& options,
+                            SkPMColor inputColorPtr[], int* inputColorCount) override {
+        if (!fCodec->rewindIfNeeded()) {
+            return SkCodec::kCouldNotRewind;
+        }
+        if (options.fSubset) {
+            // Subsets are not supported.
+            return SkCodec::kUnimplemented;
+        }
+        if (dstInfo.dimensions() != fCodec->getInfo().dimensions()) {
+            SkCodecPrintf("Error: scaling not supported.\n");
+            return SkCodec::kInvalidScale;
+        }
+        if (!conversion_possible(dstInfo, fCodec->getInfo())) {
+            SkCodecPrintf("Error: cannot convert input type to output type.\n");
+            return SkCodec::kInvalidConversion;
+        }
+
+        return fCodec->onStart(dstInfo, options, inputColorPtr, inputColorCount);
+    }
+
+    SkCodec::Result onGetScanlines(void* dst, int count, size_t rowBytes) {
+        // Create a new image info representing the portion of the image to decode
+        SkImageInfo rowInfo = this->dstInfo().makeWH(this->dstInfo().width(), count);
+
+        // Decode the requested rows
+        return fCodec->decode(rowInfo, dst, rowBytes, this->options());
+    }
+
+    // TODO(msarett): Override default skipping with something more clever.
+    // TODO(msarett): Consider other optimizations for this codec.

[scroggo, 2015/08/14 21:53:00]

Do you have any optimizations in mind?

[msarett, 2015/08/17 19:16:13]

Not in particular.  I just don't think I've analyzed this codec for anything
other than correctness.

Once the design is all set, I think it would be worth looking through and seeing
if there is anything that we can improve.

I think the memory use of the RLE codec is a good candidate.  The header tells
us how big the file is and we currently allocate that many bytes, but now that
we have checkForMoreData(), we can do better.  Also I think bmp swizzles seem
quite trivial and would be candidates for SIMD.

[scroggo, 2015/08/26 22:40:09]

Great. These would be good candidates to specifically mention as TODOs.

+
+private:
+    SkAutoTDelete<SkBmpCodec> fCodec;
+
+    typedef SkScanlineDecoder INHERITED;
+};
+
+SkScanlineDecoder* SkBmpCodec::NewSDFromStream(SkStream* stream) {
+    SkAutoTDelete<SkBmpCodec> codec(static_cast<SkBmpCodec*>(SkBmpCodec::NewFromStream(stream)));
+    if (!codec) {
+        return NULL;
+    }
+
+    return SkNEW_ARGS(SkBmpScanlineDecoder, (codec));
+}