Scanline decoding for bmp

src/codec/SkScaledCodec.cpp

Index: src/codec/SkScaledCodec.cpp
diff --git a/src/codec/SkScaledCodec.cpp b/src/codec/SkScaledCodec.cpp
index e0158b6b4ef005d035ac6ef54576debdb28b7b98..23a0082c595ac36e8cf762c1f433d4697bd4b9dc 100644
--- a/src/codec/SkScaledCodec.cpp
+++ b/src/codec/SkScaledCodec.cpp
@@ -133,6 +133,13 @@ static bool scaling_supported(const SkImageInfo& dstInfo, const SkImageInfo& src
     return true;
 }
 
+static bool is_row_necessary(int srcY, int startY, int sampleY) {

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

nit: Can you add comments explaining this function?

+    if (srcY < startY) {
+        return false;
+    }
+    return ((srcY - startY) % sampleY) == 0;
+}
+
 // calculates sampleSize in x and y direction
 void SkScaledCodec::ComputeSampleSize(const SkImageInfo& dstInfo, const SkImageInfo& srcInfo,
                                       int* sampleXPtr, int* sampleYPtr) {
@@ -221,41 +228,63 @@ SkCodec::Result SkScaledCodec::onGetPixels(const SkImageInfo& requestedInfo, voi
     if (kSuccess != result) {
         return result;
     }
-    
-    const bool requiresPostYSampling = fScanlineDecoder->requiresPostYSampling();
-
-    if (requiresPostYSampling) {
-        SkAutoMalloc storage(srcHeight * rowBytes);
-        uint8_t* storagePtr = static_cast<uint8_t*>(storage.get());
-        result = fScanlineDecoder->getScanlines(storagePtr, srcHeight, rowBytes);
-        if (kSuccess != result) {
-            return result;
-        }
-        storagePtr += Y0 * rowBytes;
-        for (int y = 0; y < dstHeight; y++) {
-            memcpy(dst, storagePtr, rowBytes);
-            storagePtr += sampleY * rowBytes;
-            dst = SkTAddOffset<void>(dst, rowBytes);
-        }
-    } else {
-        // does not require post y sampling
-        result = fScanlineDecoder->skipScanlines(Y0);
-        if (kSuccess != result) {
-            return result;
-        }
-        for (int y = 0; y < dstHeight; y++) {
-            result = fScanlineDecoder->getScanlines(dst, 1, rowBytes);
+
+    switch(fScanlineDecoder->getScanlineOrder()) {
+        case SkScanlineDecoder::kTopDown_SkScanlineOrder: {
+            result = fScanlineDecoder->skipScanlines(Y0);
             if (kSuccess != result) {
                 return result;
             }
-            if (y < dstHeight - 1) {
-                result = fScanlineDecoder->skipScanlines(sampleY - 1);
+            for (int y = 0; y < dstHeight; y++) {
+                result = fScanlineDecoder->getScanlines(dst, 1, rowBytes);
                 if (kSuccess != result) {
                     return result;
                 }
+                if (y < dstHeight - 1) {
+                    result = fScanlineDecoder->skipScanlines(sampleY - 1);
+                    if (kSuccess != result) {
+                        return result;
+                    }
+                }
+                dst = SkTAddOffset<void>(dst, rowBytes);
+            }
+            return kSuccess;
+        }
+        case SkScanlineDecoder::kOutOfOrder_SkScanlineOrder: {
+            for (int y = 0; y < srcHeight; y++) {
+                int srcY = fScanlineDecoder->getY();
+                if (is_row_necessary(srcY, Y0, sampleY)) {
+                    void* dstPtr = SkTAddOffset<void>(dst, rowBytes * (srcY / sampleY));
+                    result = fScanlineDecoder->getScanlines(dstPtr, 1, rowBytes);
+                    if (kSuccess != result) {
+                        return result;
+                    }
+                } else {
+                    result = fScanlineDecoder->skipScanlines(1);
+                    if (kSuccess != result) {
+                        return result;
+                    }
+                }
+            }
+            return kSuccess;
+        }
+        case SkScanlineDecoder::kNone_SkScanlineOrder: {
+            SkAutoMalloc storage(srcHeight * rowBytes);
+            uint8_t* storagePtr = static_cast<uint8_t*>(storage.get());
+            result = fScanlineDecoder->getScanlines(storagePtr, srcHeight, rowBytes);
+            if (kSuccess != result) {
+                return result;
+            }
+            storagePtr += Y0 * rowBytes;
+            for (int y = 0; y < dstHeight; y++) {
+                memcpy(dst, storagePtr, rowBytes);
+                storagePtr += sampleY * rowBytes;
+                dst = SkTAddOffset<void>(dst, rowBytes);
             }
-            dst = SkTAddOffset<void>(dst, rowBytes);
+            return kSuccess;
         }
+        default:
+            SkASSERT(false);
+            return kUnimplemented;
     }
-    return kSuccess;
 }