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"
 #include "SkBmpStandardCodec.h"
 #include "SkCodecPriv.h"
 #include "SkColorPriv.h"
+#include "SkScaledCodec.h"
 #include "SkStream.h"
 
 /*
  * Defines the version and type of the second bitmap header
  */
 enum BmpHeaderType {
     kInfoV1_BmpHeaderType,
     kInfoV2_BmpHeaderType,
     kInfoV3_BmpHeaderType,
     kInfoV4_BmpHeaderType,
@@ skipping 13 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 489 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)
+    {}
+
+    SkEncodedFormat onGetEncodedFormat() const override {
+        return kBMP_SkEncodedFormat;
+    }
+
+    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() != this->getInfo().dimensions()) {
+            if (!SkScaledCodec::DimensionsSupportedForSampling(this->getInfo(), dstInfo)) {
+                return SkCodec::kInvalidScale;
+            }
+        }
+        if (!conversion_possible(dstInfo, this->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) override {
+        // Create a new image info representing the portion of the image to decode
+        SkImageInfo rowInfo = this->dstInfo().makeWH(fCodec->getInfo().width(), count);
+
+        // Decode the requested rows
+        return fCodec->decode(rowInfo, dst, rowBytes, this->options());
+    }
+
+    SkScanlineOrder onGetScanlineOrder() const override {
+        if (SkBmpCodec::kTopDown_RowOrder == fCodec->fRowOrder) {
+            return kTopDown_SkScanlineOrder;
+        } else {

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

nit: This else is unnecessary. Typically, this is written as:

if (condition) {
  return enum;
}
return otherEnum;

+            return kOutOfOrder_SkScanlineOrder;
+        }
+    }
+
+    int onGetY() const override {
+        if (SkBmpCodec::kTopDown_RowOrder == fCodec->fRowOrder) {
+            return INHERITED::onGetY();
+        } else {
+            return this->dstInfo().height() - INHERITED::onGetY() - 1;
+        }
+    }
+
+    // TODO(msarett): Override default skipping with something more clever.
+    // TODO(msarett): Consider other optimizations for this codec.
+
+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.detach()));
+}