commit 238cdcdbe195fcf7bad0a4fa56e9da2e98bae505
author Pascal Massimino <pascal.massimino@gmail.com> Tue Apr 05 11:21:21 2016 +0200
committer Pascal Massimino <pascal.massimino@gmail.com> Tue Apr 05 13:12:47 2016 +0000
tree c02196bcf5235483253bc28c0aa77570c5dc17bd
parent cf6c713a0b49dc8571f6c744d53a9f4b557ca727

Only call WebPDequantizeLevels() on cropped area

this might change some crc slightly, since WebPDequantizeLevels()
performs an analysis pass, counting levels, which impacts the smoothing.
Now, the cropping area is not the same, so minor diffs are expected here
and there.

Change-Id: I3cce1e40c6f11c25b7c841044d637685c5740352

src/dec/alpha.c

diff --git a/src/dec/alpha.c b/src/dec/alpha.c
index 4a6d25e..2c32d02 100644
--- a/src/dec/alpha.c
+++ b/src/dec/alpha.c
@@ -129,7 +129,7 @@
     unfilter_func(width, height, width, row, num_rows, output);
   }
 
-  if (row + num_rows == dec->pic_hdr_.height_) {
+  if (row + num_rows >= alph_dec->io_.crop_bottom) {
     dec->is_alpha_decoded_ = 1;
   }
   return 1;
@@ -167,7 +167,7 @@
 
   assert(dec != NULL && io != NULL);
 
-  if (row < 0 || num_rows <= 0 || row + num_rows > io->height) {
+  if (row < 0 || num_rows <= 0 || row + num_rows > height) {
     return NULL;    // sanity check.
   }
 
@@ -182,22 +182,26 @@
       }
       // if we allowed use of alpha dithering, check whether it's needed at all
       if (dec->alph_dec_->pre_processing_ != ALPHA_PREPROCESSED_LEVELS) {
-        dec->alpha_dithering_ = 0;       // disable dithering
+        dec->alpha_dithering_ = 0;   // disable dithering
       } else {
-        num_rows = io->height - row;     // decode everything in one pass
+        num_rows = height - row;     // decode everything in one pass
       }
     }
 
     assert(dec->alph_dec_ != NULL);
-    assert(row + num_rows <= io->height);
+    assert(row + num_rows <= height);
     if (!ALPHDecode(dec, row, num_rows)) goto Error;
 
     if (dec->is_alpha_decoded_) {   // finished?
       ALPHDelete(dec->alph_dec_);
       dec->alph_dec_ = NULL;
       if (dec->alpha_dithering_ > 0) {
-        if (!WebPDequantizeLevels(dec->alpha_plane_, width, height, width,
-                                  dec->alpha_dithering_)) {
+        uint8_t* const alpha = dec->alpha_plane_ + io->crop_top * width
+                             + io->crop_left;
+        if (!WebPDequantizeLevels(alpha,
+                                  io->crop_right - io->crop_left,
+                                  io->crop_bottom - io->crop_top,
+                                  width, dec->alpha_dithering_)) {
           goto Error;
         }
       }