Switched to ARGB drawing in Areas on GTK+.

area.go

@@ -340,8 +340,8 @@ func pixelData(img *image.RGBA) *uint8 {
 
 // some platforms require pixels in ARGB order in their native endianness (because they treat the pixel array as an array of uint32s)
 // this does the conversion
-// you need to convert somewhere; this memory is assumed to have a stride equal to the pixels per scanline (Windows gives us memory to use; other platforms we'll see)
+// you need to convert somewhere (Windows and cairo give us memory to use; Windows has stride==width but cairo might not)
-func toARGB(i *image.RGBA, memory uintptr) {
+func toARGB(i *image.RGBA, memory uintptr, memstride int) {
 	var realbits []byte
 
 	rbs := (*reflect.SliceHeader)(unsafe.Pointer(&realbits))
@@ -352,6 +352,7 @@ func toARGB(i *image.RGBA, memory uintptr) {
 	q := 0
 	for y := i.Rect.Min.Y; y < i.Rect.Max.Y; y++ {
 		nextp := p + i.Stride
+		nextq := q + memstride
 		for x := i.Rect.Min.X; x < i.Rect.Max.X; x++ {
 			argb := uint32(i.Pix[p + 3]) << 24		// A
 			argb |= uint32(i.Pix[p + 0]) << 16		// R
@@ -367,5 +368,6 @@ func toARGB(i *image.RGBA, memory uintptr) {
 			q += 4
 		}
 		p = nextp
+		q = nextq
 	}
 }

area_unix.go

@@ -57,26 +57,27 @@ func our_area_draw_callback(widget *C.GtkWidget, cr *C.cairo_t, data C.gpointer)
 		return C.FALSE			// signals handled without stopping the event chain (thanks to desrt again)
 	}
 	i := s.handler.Paint(cliprect)
-	// pixel order is [R G B A] (see Example 1 on https://developer.gnome.org/gdk-pixbuf/2.26/gdk-pixbuf-The-GdkPixbuf-Structure.html) so we don't have to convert anything
+	surface := C.cairo_image_surface_create(
-	// gdk-pixbuf is not alpha-premultiplied (thanks to desrt in irc.gimp.net/#gtk+)
+		C.CAIRO_FORMAT_ARGB32,			// alpha-premultiplied; native byte order
-	pixbuf := C.gdk_pixbuf_new_from_data(
-		(*C.guchar)(unsafe.Pointer(pixelData(i))),
-		C.GDK_COLORSPACE_RGB,
-		C.TRUE,			// has alpha channel
-		8,				// bits per sample
 		C.int(i.Rect.Dx()),
-		C.int(i.Rect.Dy()),
+		C.int(i.Rect.Dy()))
-		C.int(i.Stride),
+	if status := C.cairo_surface_status(surface); status != C.CAIRO_STATUS_SUCCESS {
-		nil, nil)			// do not free data
+		panic(fmt.Errorf("cairo_create_image_surface() failed: %s\n",
-	C.gdk_cairo_set_source_pixbuf(cr,
+			C.GoString(C.cairo_status_to_string(status))))
-		pixbuf,
+	}
-		C.gdouble(cliprect.Min.X),
+	// the flush and mark_dirty calls are required; see the cairo docs and https://git.gnome.org/browse/gtk+/tree/gdk/gdkcairo.c#n232 (thanks desrt in irc.gimp.net/#gtk+)
-		C.gdouble(cliprect.Min.Y))
+	C.cairo_surface_flush(surface)
+	toARGB(i, uintptr(unsafe.Pointer(C.cairo_image_surface_get_data(surface))),
+		int(C.cairo_image_surface_get_stride(surface)))
+	C.cairo_surface_mark_dirty(surface)
+	C.cairo_set_source_surface(cr,
+		surface,
+		0, 0)			// origin of the surface
 	// that just set the brush that cairo uses: we have to actually draw now
 	// (via https://developer.gnome.org/gtkmm-tutorial/stable/sec-draw-images.html.en)
 	C.cairo_rectangle(cr, x, y, w, h)		// breaking the nrom here since we have the double data already
 	C.cairo_fill(cr)
-	C.g_object_unref((C.gpointer)(unsafe.Pointer(pixbuf)))		// free pixbuf
+	C.cairo_surface_destroy(surface)		// free surface
 	return C.FALSE		// signals handled without stopping the event chain (thanks to desrt again)
 }