Use bitmap width instead of scanline size in combineScanlineChannels

Change-Id: I9f5de7ed1bdcd39e5d6e580a2edbd5c0dd2027e0
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/137278
Tested-by: Jenkins
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>

1 files changed, 14 insertions, 18 deletions

diff --git a/vcl/source/filter/png/PngImageWriter.cxx b/vcl/source/filter/png/PngImageWriter.cxx
index d18c410d1359..fd5ba3c84e8e 100644
--- a/vcl/source/filter/png/PngImageWriter.cxx
+++ b/vcl/source/filter/png/PngImageWriter.cxx
@@ -15,19 +15,16 @@
 
 namespace
 {
-void combineScanlineChannels(Scanline pRGBScanline, Scanline pAlphaScanline, Scanline pResult,
-                             sal_uInt32 nSize)
+void combineScanlineChannels(Scanline pRGBScanline, Scanline pAlphaScanline,
+                             std::vector<std::remove_pointer_t<Scanline>>& pResult,
+                             sal_uInt32 nBitmapWidth)
 {
-    assert(pRGBScanline && "RGB scanline is null");
-    assert(pAlphaScanline && "Alpha scanline is null");
-
-    auto const width = nSize / 3;
-    for (sal_uInt32 i = 0; i < width; ++i)
+    for (sal_uInt32 i = 0; i < nBitmapWidth; ++i)
     {
-        *pResult++ = *pRGBScanline++; // R
-        *pResult++ = *pRGBScanline++; // G
-        *pResult++ = *pRGBScanline++; // B
-        *pResult++ = *pAlphaScanline++; // A
+        pResult[i * 4] = *pRGBScanline++; // R
+        pResult[i * 4 + 1] = *pRGBScanline++; // G
+        pResult[i * 4 + 2] = *pRGBScanline++; // B
+        pResult[i * 4 + 3] = *pAlphaScanline++; // A
     }
 }
 }
@@ -221,16 +218,15 @@ static bool pngWrite(SvStream& rStream, const BitmapEx& rBitmapEx, int nCompress
                 std::vector<std::remove_pointer_t<Scanline>> aCombinedChannels;
                 if (bCombineChannels)
                 {
-                    // Check that there's at least an alpha channel per 3 color/RGB channels
-                    assert(((pAlphaAccess->GetScanlineSize() * 3) >= pAccess->GetScanlineSize())
-                           && "RGB and alpha channel size mismatch");
+                    auto nBitmapWidth = pAccess->Width();
                     // Allocate enough size to fit all 4 channels
-                    aCombinedChannels.resize(pAlphaAccess->GetScanlineSize()
-                                             + pAccess->GetScanlineSize());
+                    aCombinedChannels.resize(nBitmapWidth * 4);
                     Scanline pAlphaPointer = pAlphaAccess->GetScanline(y);
+                    if (!pSourcePointer || !pAlphaPointer)
+                        return false;
                     // Combine RGB and alpha channels
-                    combineScanlineChannels(pSourcePointer, pAlphaPointer, aCombinedChannels.data(),
-                                            pAccess->GetScanlineSize());
+                    combineScanlineChannels(pSourcePointer, pAlphaPointer, aCombinedChannels,
+                                            nBitmapWidth);
                     pFinalPointer = aCombinedChannels.data();
                     // Invert alpha channel (255 - a)
                     png_set_invert_alpha(pPng);