Bug 1119774 (Part 2) - Add RequestDecodeForSize to imgIContainer. r=tn

image/public/imgIContainer.idl

@@ -69,7 +69,7 @@ native nsIntSizeByVal(nsIntSize);
  *
  * Internally, imgIContainer also manages animation of images.
  */
-[scriptable, builtinclass, uuid(14ea6fa5-183e-4409-ac88-110bd2e05292)]
+[scriptable, builtinclass, uuid(4adb4c92-284d-4f5a-85e7-e924ec57510f)]
 interface imgIContainer : nsISupports
 {
   /**
@@ -345,11 +345,27 @@ interface imgIContainer : nsISupports
   void requestDecode();
 
   /*
-   * This is equivalent to requestDecode() but it also decodes some of the
-   * image.
+   * This is equivalent to requestDecode() but it also synchronously decodes
+   * images that can be decoded "quickly" according to some heuristic.
    */
   [noscript] void startDecoding();
 
+  /*
+   * This method is equivalent to requestDecode(), but enables the caller to
+   * provide more detailed information about the decode request.
+   *
+   * @param aSize The size to which the image should be scaled while decoding,
+   *              if possible. If the image cannot be scaled to this size while
+   *              being decoded, it will be decoded at its intrinsic size.
+   * @param aFlags Flags of the FLAG_* variety. Only the decode flags
+   *               (FLAG_DECODE_*) and FLAG_SYNC_DECODE (which will
+   *               synchronously decode images that can be decoded "quickly",
+   *               just like startDecoding() does) are accepted; others will be
+   *               ignored.
+   */
+  [noscript] void requestDecodeForSize([const] in nsIntSize aSize,
+                                       in uint32_t aFlags);
+
   /*
    * Returns true if no more decoding can be performed on this image. Images
    * with errors return true since they cannot be decoded any further. Note that

image/src/DynamicImage.cpp

@@ -255,6 +255,12 @@ DynamicImage::StartDecoding()
   return NS_OK;
 }
 
+NS_IMETHODIMP
+DynamicImage::RequestDecodeForSize(const nsIntSize& aSize, uint32_t aFlags)
+{
+  return NS_OK;
+}
+
 bool
 DynamicImage::IsDecoded()
 {

image/src/ImageWrapper.cpp

@@ -224,6 +224,12 @@ ImageWrapper::StartDecoding()
   return mInnerImage->StartDecoding();
 }
 
+NS_IMETHODIMP
+ImageWrapper::RequestDecodeForSize(const nsIntSize& aSize, uint32_t aFlags)
+{
+  return mInnerImage->RequestDecodeForSize(aSize, aFlags);
+}
+
 bool
 ImageWrapper::IsDecoded()
 {

image/src/RasterImage.cpp

@@ -325,7 +325,7 @@ RasterImage::Init(const char* aMimeType,
   // transient images.
   MOZ_ASSERT(!(aFlags & INIT_FLAG_TRANSIENT) ||
                (!(aFlags & INIT_FLAG_DISCARDABLE) &&
-                !(aFlags & INIT_FLAG_DECODE_ON_DRAW),
+                !(aFlags & INIT_FLAG_DECODE_ON_DRAW) &&
                 !(aFlags & INIT_FLAG_DOWNSCALE_DURING_DECODE)),
              "Illegal init flags for transient image");
 
@@ -1374,24 +1374,7 @@ RasterImage::WantDecodedFrames(uint32_t aFlags, bool aShouldSyncNotify)
 NS_IMETHODIMP
 RasterImage::RequestDecode()
 {
-  MOZ_ASSERT(NS_IsMainThread());
-
-  if (mError) {
-    return NS_ERROR_FAILURE;
-  }
-  if (!mHasSize) {
-    mWantFullDecode = true;
-    return NS_OK;
-  }
-
-  // Look up the first frame of the image, which will implicitly start decoding
-  // if it's not available right now.
-  // XXX(seth): Passing false for aShouldSyncNotify here has the effect of
-  // decoding asynchronously, but that's not obvious from the argument name.
-  // This API needs to be reworked.
-  LookupFrame(0, mSize, DECODE_FLAGS_DEFAULT, /* aShouldSyncNotify = */ false);
-
-  return NS_OK;
+  return RequestDecodeForSize(mSize, DECODE_FLAGS_DEFAULT);
 }
 
 /* void startDecode() */
@@ -1403,20 +1386,38 @@ RasterImage::StartDecoding()
       NS_NewRunnableMethod(this, &RasterImage::StartDecoding));
   }
 
+  return RequestDecodeForSize(mSize, FLAG_SYNC_DECODE);
+}
+
+NS_IMETHODIMP
+RasterImage::RequestDecodeForSize(const nsIntSize& aSize, uint32_t aFlags)
+{
+  MOZ_ASSERT(NS_IsMainThread());
+
   if (mError) {
     return NS_ERROR_FAILURE;
   }
+
   if (!mHasSize) {
     mWantFullDecode = true;
     return NS_OK;
   }
 
+  // Fall back to our intrinsic size if we don't support
+  // downscale-during-decode.
+  nsIntSize targetSize = mDownscaleDuringDecode ? aSize : mSize;
+
+  // Sync decode small images if requested.
+  bool shouldSyncDecodeSmallImages = aFlags & FLAG_SYNC_DECODE;
+
   // Look up the first frame of the image, which will implicitly start decoding
   // if it's not available right now.
   // XXX(seth): Passing true for aShouldSyncNotify here has the effect of
-  // synchronously decoding small images, but that's not obvious from the
-  // argument name. This API needs to be reworked.
-  LookupFrame(0, mSize, DECODE_FLAGS_DEFAULT, /* aShouldSyncNotify = */ true);
+  // synchronously decoding small images, while passing false has the effect of
+  // decoding asynchronously, but that's not obvious from the argument name.
+  // This API needs to be reworked.
+  LookupFrame(0, targetSize, DecodeFlags(aFlags),
+              /* aShouldSyncNotify = */ shouldSyncDecodeSmallImages);
 
   return NS_OK;
 }

image/src/VectorImage.cpp

@@ -899,6 +899,15 @@ VectorImage::StartDecoding()
   return NS_OK;
 }
 
+NS_IMETHODIMP
+VectorImage::RequestDecodeForSize(const nsIntSize& aSize, uint32_t aFlags)
+{
+  // Nothing to do for SVG images, though in theory we could rasterize to the
+  // provided size ahead of time if we supported off-main-thread SVG
+  // rasterization...
+  return NS_OK;
+}
+
 bool
 VectorImage::IsDecoded()
 {