commit c5013e3870ecf5a7798c1857a3060d880a7bf2c3
author Vikas Arora <vikasa@google.com> Mon Jul 18 17:55:44 2011 +0530
committer Vikas Arora <vikasa@google.com> Mon Jul 18 17:55:44 2011 +0530
tree d5d45ad9c576f0f1155ca3e27abb2c9fafc16bdb
parent 42ab963d57980c6e82f8ef54656e41d1f656c44f

Implement on-the-fly image resizing (down-scaling).

Implement on-the-fly image resizing (down-scaling) for WebP images.
The image decoder is aware of the device memory constriant via
SampleSize set by the application like Webkit/WebCore.
sampleSize=1 implies no down-scaling. Likewise, SampleSize=2 implies
resizing image width & height by a factor of '1/2', resulting in '1/4'th
size for the decoded image.
SampleSize is merely a hint from the application to the decoder. Decoder
may choose to ignore this hint and decode the image at full scale.
Native WebP image decoder (new APIs) supports on-the-fly resizing.
Making the Skia-WebP decoder 'SampleSize' aware and implementing the
on-the-fly resizing in this change.

Change-Id: Ibbd62baf4a6ad2d3904aafb22807f4513641e64c

src/images/SkImageDecoder_libwebp.cpp

diff --git a/src/images/SkImageDecoder_libwebp.cpp b/src/images/SkImageDecoder_libwebp.cpp
index 51f8a46..7b4a39f 100644
--- a/src/images/SkImageDecoder_libwebp.cpp
+++ b/src/images/SkImageDecoder_libwebp.cpp
@@ -17,7 +17,6 @@
 #include "SkImageDecoder.h"
 #include "SkImageEncoder.h"
 #include "SkColorPriv.h"
-#include "SkDither.h"
 #include "SkScaledBitmapSampler.h"
 #include "SkStream.h"
 #include "SkTemplates.h"
@@ -133,7 +132,8 @@
 
 // Incremental WebP image decoding. Reads input buffer of 64K size iteratively
 // and decodes this block to appropriate color-space as per config object.
-static bool webp_idecode(SkStream* stream, SkBitmap* decodedBitmap) {
+static bool webp_idecode(SkStream* stream, SkBitmap* decodedBitmap,
+                         int origWidth, int origHeight) {
     SkAutoLockPixels alp(*decodedBitmap);
 
     stream->rewind();
@@ -161,6 +161,12 @@
     decode_config.output.u.RGBA.stride = decodedBitmap->rowBytes();
     decode_config.output.u.RGBA.size = decodedBitmap->getSize();
     decode_config.output.is_external_memory = 1;
+    if (origWidth != decodedBitmap->width() ||
+        origHeight != decodedBitmap->height()) {
+        decode_config.options.use_scaling = 1;
+        decode_config.options.scaled_width = decodedBitmap->width();
+        decode_config.options.scaled_height = decodedBitmap->height();
+    }
 
     WebPIDecoder* idec = WebPIDecode(NULL, NULL, &decode_config);
     if (idec == NULL) {
@@ -210,7 +216,7 @@
 }
 
 bool SkWEBPImageDecoder::setDecodeConfig(SkBitmap* decodedBitmap,
-                                         int origWidth, int origHeight) {
+                                         int width, int height) {
     bool hasAlpha = false;
     SkBitmap::Config config = this->getPrefConfig(k32Bit_SrcDepth, hasAlpha);
 
@@ -227,11 +233,11 @@
         }
     }
 
-    if (!this->chooseFromOneChoice(config, origWidth, origHeight)) {
+    if (!this->chooseFromOneChoice(config, width, height)) {
         return false;
     }
 
-    decodedBitmap->setConfig(config, origWidth, origHeight, 0);
+    decodedBitmap->setConfig(config, width, height, 0);
 
     // Current WEBP specification has no support for alpha layer.
     decodedBitmap->setIsOpaque(true);
@@ -239,7 +245,6 @@
     return true;
 }
 
-
 bool SkWEBPImageDecoder::onDecode(SkStream* stream, SkBitmap* decodedBitmap,
                                   Mode mode) {
 #ifdef TIME_DECODE
@@ -251,7 +256,11 @@
         return false;
     }
 
-    if (!setDecodeConfig(decodedBitmap, origWidth, origHeight)) {
+    const int sampleSize = this->getSampleSize();
+    SkScaledBitmapSampler sampler(origWidth, origHeight, sampleSize);
+
+    if (!setDecodeConfig(decodedBitmap, sampler.scaledWidth(),
+                         sampler.scaledHeight())) {
         return false;
     }
 
@@ -265,7 +274,7 @@
     }
 
     // Decode the WebP image data stream using WebP incremental decoding.
-    if (!webp_idecode(stream, decodedBitmap)) {
+    if (!webp_idecode(stream, decodedBitmap, origWidth, origHeight)) {
         return false;
     }