Port MinGW GCC 9.2 image.c fix to non MS-Windows

Avoid useless casts on GCC 14+ platforms on non MS-Windows, by
using a cast only if HAVE_NTGUI.  That cast should not provoke
-Wuseless-cast regardless of how MS-Windows defines HDC, since it
casts to an Emacs-defined type.  This change lets the code compile
again on Fedora 44 with --enable-gcc-warnings.
* src/dispextern.h (PIX_CONTAINER_TO_CONTEXT): New macro.
It defaults to the identity macro.
(Emacs_Pix_Context): Default to Emacs_Pix_Container.
* src/image.c (pbm_load, png_load_body, jpeg_load_body)
(tiff_load, gif_load, svg_load_image): Use the new macro
instead of a cast.

2 files changed, 16 insertions, 12 deletions

diff --git a/src/dispextern.h b/src/dispextern.h
index 4071ca57f72..129c94f0dd6 100644
--- a/src/dispextern.h
+++ b/src/dispextern.h
@@ -115,7 +115,6 @@ xstrcasecmp (char const *a, char const *b)
 typedef struct x_display_info Display_Info;
 #ifndef USE_CAIRO
 typedef XImage *Emacs_Pix_Container;
-typedef XImage *Emacs_Pix_Context;
 #endif	/* !USE_CAIRO */
 #define NativeRectangle XRectangle
 #endif
@@ -130,7 +129,6 @@ typedef struct
   int bits_per_pixel;		/* bits per pixel (ZPixmap) */
 } *Emacs_Pix_Container;
 typedef Emacs_Pix_Container Emacs_Pixmap;
-typedef Emacs_Pix_Container Emacs_Pix_Context;
 #endif
 
 #ifdef HAVE_NTGUI
@@ -138,6 +136,7 @@ typedef Emacs_Pix_Container Emacs_Pix_Context;
 typedef struct w32_display_info Display_Info;
 typedef XImage *Emacs_Pix_Container;
 typedef HDC Emacs_Pix_Context;
+# define PIX_CONTAINER_TO_CONTEXT(c) ((Emacs_Pix_Context) (c))
 #endif
 
 #ifdef HAVE_NS
@@ -145,7 +144,6 @@ typedef HDC Emacs_Pix_Context;
 /* Following typedef needed to accommodate the MSDOS port, believe it or not.  */
 typedef struct ns_display_info Display_Info;
 typedef Emacs_Pixmap Emacs_Pix_Container;
-typedef Emacs_Pixmap Emacs_Pix_Context;
 #endif
 
 #ifdef HAVE_PGTK
@@ -160,14 +158,12 @@ typedef XImagePtr XImagePtr_or_DC;
 #include "haikugui.h"
 typedef struct haiku_display_info Display_Info;
 typedef Emacs_Pixmap Emacs_Pix_Container;
-typedef Emacs_Pixmap Emacs_Pix_Context;
 #endif
 
 #ifdef HAVE_ANDROID
 #include "androidgui.h"
 typedef struct android_display_info Display_Info;
 typedef struct android_image *Emacs_Pix_Container;
-typedef struct android_image *Emacs_Pix_Context;
 #endif
 
 #ifdef HAVE_WINDOW_SYSTEM
@@ -193,6 +189,14 @@ typedef void *Emacs_Cursor;
 #  define WINDOW_HANDLE_UINTPTR(h) ((uintptr_t) {(h)})
 # endif
 
+/* Ordinarily an Emacs_Pix_Context is just an Emacs_Pix_Container;
+   platforms can override this by defining the latter type
+   and defining the conversion macro PIX_CONTAINER_TO_CONTEXT.  */
+# ifndef PIX_CONTAINER_TO_CONTEXT
+typedef Emacs_Pix_Container Emacs_Pix_Context;
+#  define PIX_CONTAINER_TO_CONTEXT(c) (c)
+# endif
+
 /* ``box'' structure similar to that found in the X sample server,
    meaning that X2 and Y2 are not actually the end of the box, but one
    pixel past the end of the box, which makes checking for overlaps
diff --git a/src/image.c b/src/image.c
index 4d6affaf849..9724094f81c 100644
--- a/src/image.c
+++ b/src/image.c
@@ -7841,7 +7841,7 @@ pbm_load (struct frame *f, struct image *img)
 
   if (NILP (image_spec_value (img->spec, QCbackground, NULL)))
     /* Casting avoids a GCC warning.  */
-    IMAGE_BACKGROUND (img, f, (Emacs_Pix_Context)ximg);
+    IMAGE_BACKGROUND (img, f, PIX_CONTAINER_TO_CONTEXT (ximg));
 
   /* Put ximg into the image.  */
   image_put_x_image (f, img, ximg, 0);
@@ -8587,7 +8587,7 @@ png_load_body (struct frame *f, struct image *img, struct png_load_context *c)
   img->height = height;
 
   /* Maybe fill in the background field while we have ximg handy.  */
-  IMAGE_BACKGROUND (img, f, (Emacs_Pix_Context)ximg);
+  IMAGE_BACKGROUND (img, f, PIX_CONTAINER_TO_CONTEXT (ximg));
 
   /* Put ximg into the image.  */
   image_put_x_image (f, img, ximg, 0);
@@ -8597,7 +8597,7 @@ png_load_body (struct frame *f, struct image *img, struct png_load_context *c)
     {
       /* Fill in the background_transparent field while we have the
 	 mask handy.  Casting avoids a GCC warning.  */
-      image_background_transparent (img, f, (Emacs_Pix_Context)mask_img);
+      image_background_transparent (img, f, PIX_CONTAINER_TO_CONTEXT (mask_img));
 
       image_put_x_image (f, img, mask_img, 1);
     }
@@ -9164,7 +9164,7 @@ jpeg_load_body (struct frame *f, struct image *img,
 
   /* Maybe fill in the background field while we have ximg handy. */
   if (NILP (image_spec_value (img->spec, QCbackground, NULL)))
-    IMAGE_BACKGROUND (img, f, (Emacs_Pix_Context)ximg);
+    IMAGE_BACKGROUND (img, f, PIX_CONTAINER_TO_CONTEXT (ximg));
 
   /* Put ximg into the image.  */
   image_put_x_image (f, img, ximg, 0);
@@ -9604,7 +9604,7 @@ tiff_load (struct frame *f, struct image *img)
 
   /* Maybe fill in the background field while we have ximg handy. */
   if (NILP (image_spec_value (img->spec, QCbackground, NULL)))
-    IMAGE_BACKGROUND (img, f, (Emacs_Pix_Context)ximg);
+    IMAGE_BACKGROUND (img, f, PIX_CONTAINER_TO_CONTEXT (ximg));
 
   /* Put ximg into the image.  */
   image_put_x_image (f, img, ximg, 0);
@@ -10326,7 +10326,7 @@ gif_load (struct frame *f, struct image *img)
 
   /* Maybe fill in the background field while we have ximg handy. */
   if (NILP (image_spec_value (img->spec, QCbackground, NULL)))
-    IMAGE_BACKGROUND (img, f, (Emacs_Pix_Context)ximg);
+    IMAGE_BACKGROUND (img, f, PIX_CONTAINER_TO_CONTEXT (ximg));
 
   /* Put ximg into the image.  */
   image_put_x_image (f, img, ximg, 0);
@@ -12510,7 +12510,7 @@ svg_load_image (struct frame *f, struct image *img, char *contents,
 
     /* Maybe fill in the background field while we have ximg handy.
        Casting avoids a GCC warning.  */
-    IMAGE_BACKGROUND (img, f, (Emacs_Pix_Context)ximg);
+    IMAGE_BACKGROUND (img, f, PIX_CONTAINER_TO_CONTEXT (ximg));
 
     /* Put ximg into the image.  */
     image_put_x_image (f, img, ximg, 0);