bug#80281: 31.0.50; FR: Canvas object as display property

On Sat, Aug 08, 2026 at 05:16:58PM +0300, Eli Zaretskii wrote:
> > From: Divya Ranjan Pattanaik <[email protected]>
> > Cc: [email protected], Daniel Mendler <[email protected]>,
> >  [email protected], [email protected], [email protected],
> >  [email protected]
> > Date: Sat, 01 Aug 2026 14:17:15 +0000
> > 
> > +@deftypefn Function uint32_t *canvas_data (emacs_env *@var{env}, emacs_value @var{canvas})
> > +The function gives access to the pixel buffer of @var{canvas}.  The
> > +pixel buffer is in row-major order with a size @var{width} * @var{height}.
> > +The pixel format is ARGB32 on all platforms.  Return @code{NULL} in case
>    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> Is this factually correct?  What about Windows, where the native
> format is BGR AFAIU?  Or is the above correct only because Windows is
> not currently supported?

Hi Eli,

as I understand it this is correct, the buffer is ARGB32. It gets
converted to the native format in canvas_prepare_for_display:

+#else
+  /* Platform independent canvas reloading.  Less efficient, since it recreates images and pixmaps. */
+  FRAME_TERMINAL (f)->free_pixmap (f, img->pixmap);
+  img->pixmap = NO_PIXMAP;
+  Emacs_Pix_Container ximg;
+  if (image_create_x_image_and_pixmap (f, img, width, height, 0, &ximg, 0))
+    {
+      for (int y = 0; y < height; ++y)
+        for (int x = 0; x < width; ++x)
+          {
+            uint32_t c = src[y * width + x],
                      ^ ARGB32
+		     r = (c >> 16) & 255,
+		     g = (c >>  8) & 255,
+		     b = c        & 255;
+            PUT_PIXEL (ximg, x, y, lookup_rgb_color (f, r << 8, g << 8, b << 8));
                                    ^ returns BGRA32, or whatever windows uses.
+          }
+      image_put_x_image (f, img, ximg, 0);
+    }
+#endif

-- 
Alan Third