fix(dds): Fix div by 0 during DXT4 DDS load (#3959)

Fixes #3950 Fix the div-by-0 when handling unassociated alpha during a DXT4 DDS load. The code mirrors what other formats do by first checking to see if the alpha value is not 0 before continuing. Added the 218-byte file from the bug to the local test suite. --------- Signed-off-by: Jesse Yurkovich <[email protected]>
AcademySoftwareFoundation · Aug 25, 2023 · a5c7a0c · a5c7a0c
1 parent 38aed29
commit a5c7a0c
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Showing 4 changed files with 20 additions and 11 deletions.
diff --git a/src/dds.imageio/ddsinput.cpp b/src/dds.imageio/ddsinput.cpp
@@ -117,12 +117,12 @@ GetBaseType(Compression cmp)
 static int
 GetChannelCount(Compression cmp, bool isNormal)
 {
-    if (isNormal)
-        return 3;
+    if (cmp == Compression::DXT5)
+        return isNormal ? 3 : 4;
+    if (cmp == Compression::BC5)
+        return isNormal ? 3 : 2;
     if (cmp == Compression::BC4)
         return 1;
-    if (cmp == Compression::BC5)
-        return 2;
     if (cmp == Compression::BC6HU || cmp == Compression::BC6HS)
         return 3;
     return 4;
@@ -788,13 +788,15 @@ DDSInput::internal_readimg(unsigned char* dst, int w, int h, int d)
             int k;
             for (int y = 0; y < h; y++) {
                 for (int x = 0; x < w; x++) {
-                    k          = (y * w + x) * 4;
-                    dst[k + 0] = (unsigned char)((int)dst[k + 0] * 255
-                                                 / (int)dst[k + 3]);
-                    dst[k + 1] = (unsigned char)((int)dst[k + 1] * 255
-                                                 / (int)dst[k + 3]);
-                    dst[k + 2] = (unsigned char)((int)dst[k + 2] * 255
-                                                 / (int)dst[k + 3]);
+                    k = (y * w + x) * 4;
+                    if (dst[k + 3]) {
+                        dst[k + 0] = (unsigned char)((int)dst[k + 0] * 255
+                                                     / (int)dst[k + 3]);
+                        dst[k + 1] = (unsigned char)((int)dst[k + 1] * 255
+                                                     / (int)dst[k + 3]);
+                        dst[k + 2] = (unsigned char)((int)dst[k + 2] * 255
+                                                     / (int)dst[k + 3]);
+                    }
                 }
             }
         }

diff --git a/testsuite/dds/ref/out.txt b/testsuite/dds/ref/out.txt
@@ -208,3 +208,9 @@ src/crash-1634.dds   :   16 x    8, 1 channel, uint8 dds
 oiiotool ERROR: read : "src/crash-1635.dds": Unsupported DDS bit depth: 1048576 (maybe it's a corrupted file?)
 Full command line was:
 > oiiotool --info -v -a --hash src/crash-1635.dds
+Reading src/crash-3950.dds
+src/crash-3950.dds   :   16 x    1, 4 channel, uint8 dds
+    SHA-1: EAAFC1B407635293A2F156CCBA32225D37469178
+    channel list: R, G, B, A
+    compression: "DXT4"
+    textureformat: "Plain Texture"
diff --git a/testsuite/dds/run.py b/testsuite/dds/run.py
@@ -51,3 +51,4 @@
 # Test more corrupted files or those that used to crash
 command += info_command ("src/crash-1634.dds", hash=True)
 command += info_command ("src/crash-1635.dds", hash=True)
+command += info_command ("src/crash-3950.dds", hash=True)
diff --git a/testsuite/dds/src/crash-3950.dds b/testsuite/dds/src/crash-3950.dds