add support for reading alpha channel from BMP images (#9741)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@54942 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

diff --git a/src/common/imagbmp.cpp b/src/common/imagbmp.cpp
index 66718fc518fb63bd974134aeeb4b9c4e4669527f..fc67b7731307c719f5972214b05f943708c4929b 100644 (file)
--- a/src/common/imagbmp.cpp
+++ b/src/common/imagbmp.cpp
@@ -479,9 +479,9 @@ bool wxBMPHandler::DoLoadDib(wxImage * image, int width, int height,
                              wxFileOffset bmpOffset, wxInputStream& stream,
                              bool verbose, bool IsBmp, bool hasPalette)
 {
-    wxInt32         aDword, rmask = 0, gmask = 0, bmask = 0;
-    int             rshift = 0, gshift = 0, bshift = 0;
-    int             rbits = 0, gbits = 0, bbits = 0;
+    wxInt32         aDword, rmask = 0, gmask = 0, bmask = 0, amask = 0;
+    int             rshift = 0, gshift = 0, bshift = 0, ashift = 0;
+    int             rbits = 0, gbits = 0, bbits = 0, abits = 0;
     wxInt32         dbuf[4];
     wxInt8          bbuf[4];
     wxUint8         aByte;
@@ -513,11 +513,29 @@ bool wxBMPHandler::DoLoadDib(wxImage * image, int width, int height,
     {
         if ( verbose )
             wxLogError( _("BMP: Couldn't allocate memory.") );
-        if ( cmap )
-            delete[] cmap;
+        delete[] cmap;
         return false;
     }
 
+    unsigned char *alpha;
+    if ( bpp == 32 )
+    {
+        // tell the image to allocate an alpha buffer
+        image->SetAlpha();
+        alpha = image->GetAlpha();
+        if ( !alpha )
+        {
+            if ( verbose )
+                wxLogError(_("BMP: Couldn't allocate memory."));
+            delete[] cmap;
+            return false;
+        }
+    }
+    else // no alpha
+    {
+        alpha = NULL;
+    }
+
     // Reading the palette, if it exists:
     if ( bpp < 16 && ncolors != 0 )
     {
@@ -602,9 +620,13 @@ bool wxBMPHandler::DoLoadDib(wxImage * image, int width, int height,
             rmask = 0x00FF0000;
             gmask = 0x0000FF00;
             bmask = 0x000000FF;
+            amask = 0xFF000000;
+
+            ashift = 24;
             rshift = 16;
             gshift = 8;
             bshift = 0;
+            abits = 8;
             rbits = 8;
             gbits = 8;
             bbits = 8;
@@ -840,6 +862,11 @@ bool wxBMPHandler::DoLoadDib(wxImage * image, int width, int height,
                 ptr[poffset + 1] = temp;
                 temp = (unsigned char)((aDword & bmask) >> bshift);
                 ptr[poffset + 2] = temp;
+                if ( alpha )
+                {
+                    temp = (unsigned char)((aDword & amask) >> ashift);
+                    alpha[line * width + column] = temp;
+                }
                 column++;
             }
         }