3 files changed, 52 insertions, 21 deletions

diff --git a/include/images/SkImageDecoder.h b/include/images/SkImageDecoder.h
index 3c904ca..0f71a3f 100644
--- a/include/images/SkImageDecoder.h
+++ b/include/images/SkImageDecoder.h
@@ -205,9 +205,9 @@ public:
 
         note: document use of Allocator, Peeker and Chooser
     */
-    bool decode(SkStream*, SkBitmap* bitmap, SkBitmap::Config pref, Mode);
-    bool decode(SkStream* stream, SkBitmap* bitmap, Mode mode) {
-        return this->decode(stream, bitmap, SkBitmap::kNo_Config, mode);
+    bool decode(SkStream*, SkBitmap* bitmap, SkBitmap::Config pref, Mode, bool reuseBitmap = false);
+    bool decode(SkStream* stream, SkBitmap* bitmap, Mode mode, bool reuseBitmap = false) {
+        return this->decode(stream, bitmap, SkBitmap::kNo_Config, mode, reuseBitmap);
     }
 
     /**
diff --git a/src/images/SkImageDecoder.cpp b/src/images/SkImageDecoder.cpp
index 7713e86..a46471b 100644
--- a/src/images/SkImageDecoder.cpp
+++ b/src/images/SkImageDecoder.cpp
@@ -153,7 +153,9 @@ SkBitmap::Config SkImageDecoder::getPrefConfig(SrcDepth srcDepth,
 }
 
 bool SkImageDecoder::decode(SkStream* stream, SkBitmap* bm,
-                            SkBitmap::Config pref, Mode mode) {
+                            SkBitmap::Config pref, Mode mode, bool reuseBitmap) {
+    SkAutoLockPixels alp(*bm);
+    bool hasPixels = (bm->getPixels() != NULL);
     // pass a temporary bitmap, so that if we return false, we are assured of
     // leaving the caller's bitmap untouched.
     SkBitmap    tmp;
@@ -163,10 +165,16 @@ bool SkImageDecoder::decode(SkStream* stream, SkBitmap* bm,
     // assign this, for use by getPrefConfig(), in case fUsePrefTable is false
     fDefaultPref = pref;
 
-    if (!this->onDecode(stream, &tmp, mode)) {
-        return false;
+    if (reuseBitmap && hasPixels) {
+        if (!this->onDecode(stream, bm, mode)) {
+            return false;
+        }
+    } else {
+        if (!this->onDecode(stream, &tmp, mode)) {
+            return false;
+        }
+        bm->swap(tmp);
     }
-    bm->swap(tmp);
     return true;
 }
 
diff --git a/src/images/SkImageDecoder_libjpeg.cpp b/src/images/SkImageDecoder_libjpeg.cpp
index 7e425c1..358861e 100644
--- a/src/images/SkImageDecoder_libjpeg.cpp
+++ b/src/images/SkImageDecoder_libjpeg.cpp
@@ -325,16 +325,26 @@ bool SkJPEGImageDecoder::onDecode(SkStream* stream, SkBitmap* bm, Mode mode) {
         (config == SkBitmap::kRGB_565_Config && 
                 cinfo.out_color_space == JCS_RGB_565)))
     {
-        bm->setConfig(config, cinfo.output_width, cinfo.output_height);
-        bm->setIsOpaque(true);
-        if (SkImageDecoder::kDecodeBounds_Mode == mode) {
+        bm->lockPixels();
+        JSAMPLE* rowptr = (JSAMPLE*)bm->getPixels();
+        bm->unlockPixels();
+        bool reuseBitmap = (rowptr != NULL && (int) cinfo.output_width == bm->width() &&
+                (int) cinfo.output_height == bm->height());
+
+        if (!reuseBitmap) {
+            bm->setConfig(config, cinfo.output_width, cinfo.output_height);
+            bm->setIsOpaque(true);
+            if (SkImageDecoder::kDecodeBounds_Mode == mode) {
+                return true;
+            }
+            if (!this->allocPixelRef(bm, NULL)) {
+                return return_false(cinfo, *bm, "allocPixelRef");
+            }
+        } else if (SkImageDecoder::kDecodeBounds_Mode == mode) {
             return true;
         }
-        if (!this->allocPixelRef(bm, NULL)) {
-            return return_false(cinfo, *bm, "allocPixelRef");
-        }
         SkAutoLockPixels alp(*bm);
-        JSAMPLE* rowptr = (JSAMPLE*)bm->getPixels();
+        rowptr = (JSAMPLE*)bm->getPixels();
         INT32 const bpr =  bm->rowBytes();
         
         while (cinfo.output_scanline < cinfo.output_height) {
@@ -349,6 +359,9 @@ bool SkJPEGImageDecoder::onDecode(SkStream* stream, SkBitmap* bm, Mode mode) {
             }
             rowptr += bpr;
         }
+        if (reuseBitmap) {
+            bm->notifyPixelsChanged();
+        }
         jpeg_finish_decompress(&cinfo);
         return true;
     }
@@ -374,16 +387,26 @@ bool SkJPEGImageDecoder::onDecode(SkStream* stream, SkBitmap* bm, Mode mode) {
     SkScaledBitmapSampler sampler(cinfo.output_width, cinfo.output_height,
                                   sampleSize);
 
-    bm->setConfig(config, sampler.scaledWidth(), sampler.scaledHeight());
-    // jpegs are always opauqe (i.e. have no per-pixel alpha)
-    bm->setIsOpaque(true);
+    bm->lockPixels();
+    JSAMPLE* rowptr = (JSAMPLE*)bm->getPixels();
+    bool reuseBitmap = (rowptr != NULL && sampler.scaledWidth() == bm->width() &&
+            sampler.scaledHeight() == bm->height());
+    bm->unlockPixels();
+
+    if (!reuseBitmap) {
+        bm->setConfig(config, sampler.scaledWidth(), sampler.scaledHeight());
+        // jpegs are always opaque (i.e. have no per-pixel alpha)
+        bm->setIsOpaque(true);
 
-    if (SkImageDecoder::kDecodeBounds_Mode == mode) {
+        if (SkImageDecoder::kDecodeBounds_Mode == mode) {
+            return true;
+        }
+        if (!this->allocPixelRef(bm, NULL)) {
+            return return_false(cinfo, *bm, "allocPixelRef");
+        }
+    } else if (SkImageDecoder::kDecodeBounds_Mode == mode) {
         return true;
     }
-    if (!this->allocPixelRef(bm, NULL)) {
-        return return_false(cinfo, *bm, "allocPixelRef");
-    }
 
     SkAutoLockPixels alp(*bm);                          
     if (!sampler.begin(bm, sc, this->getDitherImage())) {