Scanline decoding for bmp

src/codec/SkBmpCodec.cpp

Index: src/codec/SkBmpCodec.cpp
diff --git a/src/codec/SkBmpCodec.cpp b/src/codec/SkBmpCodec.cpp
index fa4608ffeec513cacd753fc3efc721497d1eff3c..addcc80102d481265a220eeb151980e9138c55c3 100644
--- a/src/codec/SkBmpCodec.cpp
+++ b/src/codec/SkBmpCodec.cpp
@@ -44,16 +44,6 @@ enum BmpCompressionMethod {
 };
 
 /*
- * 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) {
@@ -472,7 +462,7 @@ bool SkBmpCodec::ReadHeader(SkStream* stream, bool inIco, SkCodec** codecOut) {
         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:
@@ -490,7 +480,7 @@ bool SkBmpCodec::ReadHeader(SkStream* stream, bool inIco, SkCodec** codecOut) {
                 }
 
                 *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
@@ -499,7 +489,7 @@ bool SkBmpCodec::ReadHeader(SkStream* stream, bool inIco, SkCodec** codecOut) {
                 // 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:
@@ -529,8 +519,9 @@ SkCodec* SkBmpCodec::NewFromStream(SkStream* stream, bool inIco) {
 }
 
 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)
 {}
@@ -562,3 +553,60 @@ uint32_t SkBmpCodec::computeNumColors(uint32_t numColors) {
     }
     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));
+}