Bug 1045929 (Part 2) - Implement downscale-during-decode for JPEG images. r=tn

image/decoders/nsJPEGDecoder.cpp

@@ -139,6 +139,20 @@ nsJPEGDecoder::SpeedHistogram()
   return Telemetry::IMAGE_DECODE_SPEED_JPEG;
 }
 
+nsresult
+nsJPEGDecoder::SetTargetSize(const nsIntSize& aSize)
+{
+  // Make sure the size is reasonable.
+  if (MOZ_UNLIKELY(aSize.width <= 0 || aSize.height <= 0)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Create a downscaler that we'll filter our output through.
+  mDownscaler.emplace(aSize);
+
+  return NS_OK;
+}
+
 void
 nsJPEGDecoder::InitInternal()
 {
@@ -394,6 +408,17 @@ nsJPEGDecoder::WriteInternal(const char* aBuffer, uint32_t aCount)
       return;
     }
 
+    if (mDownscaler) {
+      nsresult rv = mDownscaler->BeginFrame(GetSize(),
+                                            mImageData,
+                                            /* aHasAlpha = */ false);
+      if (NS_FAILED(rv)) {
+        mState = JPEG_ERROR;
+        return;
+      }
+    }
+
+
     PR_LOG(GetJPEGDecoderAccountingLog(), PR_LOG_DEBUG,
            ("        JPEGDecoderAccounting: nsJPEGDecoder::"
             "Write -- created image frame with %ux%u pixels",
@@ -512,6 +537,7 @@ nsJPEGDecoder::WriteInternal(const char* aBuffer, uint32_t aCount)
             break;
 
           mInfo.output_scanline = 0;
+          mDownscaler->ResetForNextProgressivePass();
         }
       }
 
@@ -591,9 +617,15 @@ nsJPEGDecoder::OutputScanlines(bool* suspend)
   const uint32_t top = mInfo.output_scanline;
 
   while ((mInfo.output_scanline < mInfo.output_height)) {
-      // Use the Cairo image buffer as scanline buffer
-      uint32_t* imageRow = ((uint32_t*)mImageData) +
-                           (mInfo.output_scanline * mInfo.output_width);
+      uint32_t* imageRow = nullptr;
+      if (mDownscaler) {
+        imageRow = reinterpret_cast<uint32_t*>(mDownscaler->RowBuffer());
+      } else {
+        imageRow = reinterpret_cast<uint32_t*>(mImageData) +
+                   (mInfo.output_scanline * mInfo.output_width);
+      }
+
+      MOZ_ASSERT(imageRow, "Should have a row buffer here");
 
       if (mInfo.out_color_space == MOZ_JCS_EXT_NATIVE_ENDIAN_XRGB) {
         // Special case: scanline will be directly converted into packed ARGB
@@ -601,6 +633,9 @@ nsJPEGDecoder::OutputScanlines(bool* suspend)
           *suspend = true; // suspend
           break;
         }
+        if (mDownscaler) {
+          mDownscaler->CommitRow();
+        }
         continue; // all done for this row!
       }
 
@@ -676,13 +711,22 @@ nsJPEGDecoder::OutputScanlines(bool* suspend)
                                      sampleRow[2]);
         sampleRow += 3;
       }
+
+      if (mDownscaler) {
+        mDownscaler->CommitRow();
+      }
   }
 
   if (top != mInfo.output_scanline) {
-      nsIntRect r(0, top, mInfo.output_width, mInfo.output_scanline-top);
-      PostInvalidation(r);
+    PostInvalidation(nsIntRect(0, top,
+                               mInfo.output_width,
+                               mInfo.output_scanline - top),
+                     mDownscaler ? Some(mDownscaler->TakeInvalidRect())
+                                 : Nothing());
   }
 
+  MOZ_ASSERT(!mDownscaler || !mDownscaler->HasInvalidation(),
+             "Didn't send downscaler's invalidation");
 }
 
 

image/decoders/nsJPEGDecoder.h

@@ -15,6 +15,7 @@
 
 #include "Decoder.h"
 
+#include "Downscaler.h"
 #include "nsAutoPtr.h"
 
 #include "nsIInputStream.h"
@@ -55,6 +56,8 @@ public:
   nsJPEGDecoder(RasterImage* aImage, Decoder::DecodeStyle aDecodeStyle);
   virtual ~nsJPEGDecoder();
 
+  virtual nsresult SetTargetSize(const nsIntSize& aSize) MOZ_OVERRIDE;
+
   virtual void InitInternal() MOZ_OVERRIDE;
   virtual void WriteInternal(const char* aBuffer, uint32_t aCount) MOZ_OVERRIDE;
   virtual void FinishInternal() MOZ_OVERRIDE;
@@ -66,6 +69,8 @@ protected:
   Orientation ReadOrientationFromEXIF();
   void OutputScanlines(bool* suspend);
 
+  Maybe<Downscaler> mDownscaler;
+
 public:
   struct jpeg_decompress_struct mInfo;
   struct jpeg_source_mgr mSourceMgr;

image/src/ImageFactory.cpp

@@ -34,8 +34,9 @@ ImageFactory::Initialize()
 static bool
 ShouldDownscaleDuringDecode(const nsCString& aMimeType)
 {
-  // Not enabled for anything yet.
-  return false;
+  return aMimeType.EqualsLiteral(IMAGE_JPEG) ||
+         aMimeType.EqualsLiteral(IMAGE_JPG) ||
+         aMimeType.EqualsLiteral(IMAGE_PJPEG);
 }
 
 static uint32_t