From: Robin Dunn <robin@alldunn.com>
Date: Tue, 29 Jul 2003 18:47:38 +0000 (+0000)
Subject: Two fixes for CheckTransparency.  First, don't start checking from
X-Git-Url: https://git.saurik.com/wxWidgets.git/commitdiff_plain/e45cc23511d0488774a00b1693aaa6881f37dfb6

Two fixes for CheckTransparency.  First, don't start checking from
(x+1,y) since you don't know if (x,y) is transparent or not.  Second,
use x*(numColBytes+1) instead of just x to offset into the first
line.


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@22368 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
---

diff --git a/src/common/imagpng.cpp b/src/common/imagpng.cpp
index 66e917422a..99db62ed93 100644
--- a/src/common/imagpng.cpp
+++ b/src/common/imagpng.cpp
@@ -220,14 +220,13 @@ CheckTransparency(unsigned char **lines,
                   png_uint_32 x, png_uint_32 y, png_uint_32 w, png_uint_32 h,
                   size_t numColBytes)
 {
-    // we start from (x + 1, y)
-    x++;
-
     // suppose that a mask will suffice and check all the remaining alpha
     // values to see if it does
     for ( ; y < h; y++ )
     {
-        unsigned const char *ptr = lines[y] + x;
+        // each pixel is numColBytes+1 bytes, offset into the current line by
+        // the current x position
+        unsigned const char *ptr = lines[y] + (x * (numColBytes + 1));
 
         for ( png_uint_32 x2 = x; x2 < w; x2++ )
         {