windowscodecs: Implemented GifFrameDecode_GetResolution.

dlls/windowscodecs/gifformat.c

@@ -123,8 +123,15 @@ static HRESULT WINAPI GifFrameDecode_GetPixelFormat(IWICBitmapFrameDecode *iface
 static HRESULT WINAPI GifFrameDecode_GetResolution(IWICBitmapFrameDecode *iface,
     double *pDpiX, double *pDpiY)
 {
-    FIXME("(%p,%p,%p): stub\n", iface, pDpiX, pDpiY);
-    return E_NOTIMPL;
+    GifFrameDecode *This = (GifFrameDecode*)iface;
+    const GifWord aspect_word = This->parent->gif->SAspectRatio;
+    const double aspect = (aspect_word > 0) ? ((aspect_word + 15.0) / 64.0) : 1.0;
+    TRACE("(%p,%p,%p)\n", iface, pDpiX, pDpiY);
+
+    *pDpiX = 96.0 / aspect;
+    *pDpiY = 96.0;
+
+    return S_OK;
 }
 
 static HRESULT WINAPI GifFrameDecode_CopyPalette(IWICBitmapFrameDecode *iface,

dlls/windowscodecs/ungif.c

@@ -285,6 +285,7 @@ DGifGetScreenDesc(GifFileType * GifFile) {
     GifFile->SColorResolution = (((Buf[0] & 0x70) + 1) >> 4) + 1;
     BitsPerPixel = (Buf[0] & 0x07) + 1;
     GifFile->SBackGroundColor = Buf[1];
+    GifFile->SAspectRatio = Buf[2];
     if (Buf[0] & 0x80) {    /* Do we have global color map? */
 
         GifFile->SColorMap = MakeMapObject(1 << BitsPerPixel, NULL);

dlls/windowscodecs/ungif.h

@@ -100,7 +100,8 @@ typedef struct GifImageDesc {
 typedef struct GifFileType {
     GifWord SWidth, SHeight,        /* Screen dimensions. */
       SColorResolution,         /* How many colors can we generate? */
-      SBackGroundColor;         /* I hope you understand this one... */
+      SBackGroundColor,         /* I hope you understand this one... */
+      SAspectRatio;             /* Pixel aspect ratio, in 1/64 units, starting at 1:4. */
     ColorMapObject *SColorMap;  /* NULL if not exists. */
     int ImageCount;             /* Number of current image */
     GifImageDesc Image;         /* Block describing current image */