render/egl: stop advertising render support for external-only formats

Some formats like YUV are only supported by Mesa for sampling, not
for rendering. However we always unconditionally added the INVALID
modifier to the list of render formats.

Check whether all modifiers are external-only, in that case, don't
add INVALID to the list of render formats.

render/egl.c

@@ -136,11 +136,25 @@ static void init_dmabuf_formats(struct wlr_egl *egl) {
 
 		has_modifiers = has_modifiers || modifiers_len > 0;
 
-		// EGL always supports implicit modifiers
+		bool all_external_only = true;
+		for (int j = 0; j < modifiers_len; j++) {
+			wlr_drm_format_set_add(&egl->dmabuf_texture_formats, fmt,
+				modifiers[j]);
+			if (!external_only[j]) {
+				wlr_drm_format_set_add(&egl->dmabuf_render_formats, fmt,
+					modifiers[j]);
+				all_external_only = false;
+			}
+		}
+
+		// EGL always supports implicit modifiers. If at least one modifier supports rendering,
+		// assume the implicit modifier supports rendering too.
 		wlr_drm_format_set_add(&egl->dmabuf_texture_formats, fmt,
 			DRM_FORMAT_MOD_INVALID);
-		wlr_drm_format_set_add(&egl->dmabuf_render_formats, fmt,
+		if (modifiers_len == 0 || !all_external_only) {
-			DRM_FORMAT_MOD_INVALID);
+			wlr_drm_format_set_add(&egl->dmabuf_render_formats, fmt,
+				DRM_FORMAT_MOD_INVALID);
+		}
 
 		if (modifiers_len == 0) {
 			// Asume the linear layout is supported if the driver doesn't
@@ -151,15 +165,6 @@ static void init_dmabuf_formats(struct wlr_egl *egl) {
 				DRM_FORMAT_MOD_LINEAR);
 		}
 
-		for (int j = 0; j < modifiers_len; j++) {
-			wlr_drm_format_set_add(&egl->dmabuf_texture_formats, fmt,
-				modifiers[j]);
-			if (!external_only[j]) {
-				wlr_drm_format_set_add(&egl->dmabuf_render_formats, fmt,
-					modifiers[j]);
-			}
-		}
-
 		if (wlr_log_get_verbosity() >= WLR_DEBUG) {
 			char *fmt_name = drmGetFormatName(fmt);
 			wlr_log(WLR_DEBUG, "  %s (0x%08"PRIX32")",