From: Dimitri Schoolwerth <dimitri.schoolwerth@gmail.com>
Date: Wed, 17 Aug 2011 21:01:09 +0000 (+0000)
Subject: Improved BMP decoding.
X-Git-Url: https://git.saurik.com/wxWidgets.git/commitdiff_plain/d06c3098ab6add89fbee763416d5e5546c66fe23

Improved BMP decoding.

The BMP decoder did not handle images that are not stored upside down but straight up (in which case the height is negative). Also with RLE4 or RLE8 compressed images the 'end of scanline' RLE marker was not handled correctly. Fixed the issues and added a unit test for them.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68766 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
---

diff --git a/src/common/imagbmp.cpp b/src/common/imagbmp.cpp
index 631130805c..f3c7f8c040 100644
--- a/src/common/imagbmp.cpp
+++ b/src/common/imagbmp.cpp
@@ -533,6 +533,14 @@ bool wxBMPHandler::DoLoadDib(wxImage * image, int width, int height,
 
     wxON_BLOCK_EXIT1(&BMPPalette::Free, cmap);
 
+    bool isUpsideDown = true;
+
+    if (height < 0)
+    {
+        isUpsideDown = false;
+        height = -height;
+    }
+
     // destroy existing here instead of:
     image->Destroy();
     image->Create(width, height);
@@ -702,9 +710,10 @@ bool wxBMPHandler::DoLoadDib(wxImage * image, int width, int height,
     // this case (see #10915)
     bool hasValidAlpha = false;
 
-    /* BMPs are stored upside down */
-    for ( int line = (height - 1); line >= 0; line-- )
+    for ( int row = 0; row < height; row++ )
     {
+        int line = isUpsideDown ? height - 1 - row : row;
+
         int linepos = 0;
         for ( int column = 0; column < width ; )
         {
@@ -734,21 +743,24 @@ bool wxBMPHandler::DoLoadDib(wxImage * image, int width, int height,
                         {
                             if ( aByte == 0 )
                             {
-                                if ( column > 0 )
-                                    column = width;
+                                // end of scanline marker
+                                column = width;
+                                row--;
                             }
                             else if ( aByte == 1 )
                             {
+                                // end of RLE data marker, stop decoding
                                 column = width;
-                                line = -1;
+                                row = height;
                             }
                             else if ( aByte == 2 )
                             {
+                                // delta marker, move in image
                                 aByte = stream.GetC();
                                 column += aByte;
                                 linepos = column * bpp / 4;
                                 aByte = stream.GetC();
-                                line -= aByte; // upside down
+                                row += aByte; // upside down
                             }
                             else
                             {
@@ -817,20 +829,24 @@ bool wxBMPHandler::DoLoadDib(wxImage * image, int width, int height,
                         {
                             if ( aByte == 0 )
                             {
-                                /* column = width; */
+                                // end of scanline marker
+                                column = width;
+                                row--;
                             }
                             else if ( aByte == 1 )
                             {
+                                // end of RLE data marker, stop decoding
                                 column = width;
-                                line = -1;
+                                row = height;
                             }
                             else if ( aByte == 2 )
                             {
+                                // delta marker, move in image
                                 aByte = stream.GetC();
                                 column += aByte;
                                 linepos = column * bpp / 8;
                                 aByte = stream.GetC();
-                                line += aByte;
+                                row -= aByte;
                             }
                             else
                             {
diff --git a/tests/image/horse_grey.bmp b/tests/image/horse_grey.bmp
new file mode 100644
index 0000000000..b99ffd63ba
Binary files /dev/null and b/tests/image/horse_grey.bmp differ
diff --git a/tests/image/horse_grey_flipped.bmp b/tests/image/horse_grey_flipped.bmp
new file mode 100644
index 0000000000..7cd67f3cb3
Binary files /dev/null and b/tests/image/horse_grey_flipped.bmp differ
diff --git a/tests/image/horse_rle4.bmp b/tests/image/horse_rle4.bmp
new file mode 100644
index 0000000000..bdc43a1f36
Binary files /dev/null and b/tests/image/horse_rle4.bmp differ
diff --git a/tests/image/horse_rle4_flipped.bmp b/tests/image/horse_rle4_flipped.bmp
new file mode 100644
index 0000000000..6f23188428
Binary files /dev/null and b/tests/image/horse_rle4_flipped.bmp differ
diff --git a/tests/image/horse_rle8.bmp b/tests/image/horse_rle8.bmp
new file mode 100644
index 0000000000..31dfc87571
Binary files /dev/null and b/tests/image/horse_rle8.bmp differ
diff --git a/tests/image/horse_rle8_flipped.bmp b/tests/image/horse_rle8_flipped.bmp
new file mode 100644
index 0000000000..bd16370397
Binary files /dev/null and b/tests/image/horse_rle8_flipped.bmp differ
diff --git a/tests/image/image.cpp b/tests/image/image.cpp
index 6b98ad4f3c..ae63591d8e 100644
--- a/tests/image/image.cpp
+++ b/tests/image/image.cpp
@@ -77,6 +77,7 @@ private:
         CPPUNIT_TEST( ReadCorruptedTGA );
         CPPUNIT_TEST( GIFComment );
         CPPUNIT_TEST( DibPadding );
+        CPPUNIT_TEST( BMPFlippingAndRLECompression );
     CPPUNIT_TEST_SUITE_END();
 
     void LoadFromSocketStream();
@@ -90,6 +91,7 @@ private:
     void ReadCorruptedTGA();
     void GIFComment();
     void DibPadding();
+    void BMPFlippingAndRLECompression();
 
     DECLARE_NO_COPY_CLASS(ImageTestCase)
 };
@@ -1262,6 +1264,26 @@ void ImageTestCase::DibPadding()
     CPPUNIT_ASSERT( image.SaveFile(memOut, wxBITMAP_TYPE_ICO) );
 }
 
+static void CompareBMPImage(const wxString& file1, const wxString& file2)
+{
+    wxImage image1(file1);
+    CPPUNIT_ASSERT( image1.IsOk() );
+
+    wxImage image2(file2);
+    CPPUNIT_ASSERT( image2.IsOk() );
+
+    CompareImage(*wxImage::FindHandler(wxBITMAP_TYPE_BMP), image1, 0, &image2);
+}
+
+void ImageTestCase::BMPFlippingAndRLECompression()
+{
+    CompareBMPImage("image/horse_grey.bmp", "image/horse_grey_flipped.bmp");
+
+    CompareBMPImage("image/horse_rle8.bmp", "image/horse_grey.bmp");
+    CompareBMPImage("image/horse_rle8.bmp", "image/horse_rle8_flipped.bmp");
+
+    CompareBMPImage("image/horse_rle4.bmp", "image/horse_rle4_flipped.bmp");
+}
 #endif //wxUSE_IMAGE