Add subsetting to SkScaledCodec

src/codec/SkWebpCodec.cpp

Index: src/codec/SkWebpCodec.cpp
diff --git a/src/codec/SkWebpCodec.cpp b/src/codec/SkWebpCodec.cpp
index a0fab0a153d67f0d32375ac7405d06314a7bb317..e5dc62a2162b9fdd2ece5de3da91ff44ee2b9eed 100644
--- a/src/codec/SkWebpCodec.cpp
+++ b/src/codec/SkWebpCodec.cpp
@@ -140,15 +140,6 @@ static WEBP_CSP_MODE webp_decode_mode(SkColorType ct, bool premultiply) {
 static const size_t BUFFER_SIZE = 4096;
 
 bool SkWebpCodec::onGetValidSubset(SkIRect* desiredSubset) const {
-    if (!desiredSubset) {
-        return false;
-    }
-
-    SkIRect bounds = SkIRect::MakeSize(this->getInfo().dimensions());
-    if (!desiredSubset->intersect(bounds)) {
-        return false;
-    }
-
     // As stated below, libwebp snaps to even left and top. Make sure top and left are even, so we
     // decode this exact subset.
     // Leave right and bottom unmodified, so we suggest a slightly larger subset than requested.
@@ -157,6 +148,25 @@ bool SkWebpCodec::onGetValidSubset(SkIRect* desiredSubset) const {
     return true;
 }
 
+bool SkWebpCodec::onGetScaledSubsetDimensions(float desiredScale, Options* options) const {
+    if (!this->onGetValidSubset(options->fSubset)) {
+        return false;
+    }
+    options->fScaledDimensions = SkISize::Make(
+            SkTMax(1, SkScalarRoundToInt(desiredScale * this->getInfo().width())),
+            SkTMax(1, SkScalarRoundToInt(desiredScale * this->getInfo().height())));
+    // Notice that we may round the size of the subset up to 1.  This means that we must
+    // floor the left and top offsets to ensure that we do not suggest a subset that is
+    // off the edge of the image.
+    options->fScaledSubset = SkIRect::MakeXYWH(
+            int (desiredScale * options->fSubset->left()),
+            int (desiredScale * options->fSubset->top()),
+            SkTMax(1, SkScalarRoundToInt(desiredScale * options->fSubset->width())),
+            SkTMax(1, SkScalarRoundToInt(desiredScale * options->fSubset->height())));
+
+    return true;
+}
+
 SkCodec::Result SkWebpCodec::onGetPixels(const SkImageInfo& dstInfo, void* dst, size_t rowBytes,
                                          const Options& options, SkPMColor*, int*,
                                          int* rowsDecoded) {
@@ -222,7 +232,10 @@ SkCodec::Result SkWebpCodec::onGetPixels(const SkImageInfo& dstInfo, void* dst,
             dstInfo.alphaType() == kPremul_SkAlphaType);
     config.output.u.RGBA.rgba = (uint8_t*) dst;
     config.output.u.RGBA.stride = (int) rowBytes;
-    config.output.u.RGBA.size = dstInfo.getSafeSize(rowBytes);
+    // TODO: We can use dstInfo.getSafeSize(rowBytes) here because
+    //       https://code.google.com/p/webp/issues/detail?id=258 has
+    //       been resolved, but it will require an update to libwebp.
+    config.output.u.RGBA.size = rowBytes * dstInfo.height();
     config.output.is_external_memory = 1;
 
     SkAutoTCallVProc<WebPIDecoder, WebPIDelete> idec(WebPIDecode(nullptr, 0, &config));