output: lift up output format fallback logic

This makes it possible for the two functions using output_pick_format
(output_pick_cursor_format and output_create_swapchain) to select
different buffer formats.

include/types/wlr_output.h

@@ -8,7 +8,7 @@ void output_pending_resolution(struct wlr_output *output, int *width,
 	int *height);
 
 struct wlr_drm_format *output_pick_format(struct wlr_output *output,
-	const struct wlr_drm_format_set *display_formats);
+	const struct wlr_drm_format_set *display_formats, uint32_t format);
 void output_clear_back_buffer(struct wlr_output *output);
 bool output_ensure_buffer(struct wlr_output *output);
 

types/output/cursor.c

@@ -206,7 +206,13 @@ static struct wlr_drm_format *output_pick_cursor_format(struct wlr_output *outpu
 		}
 	}
 
-	return output_pick_format(output, display_formats);
+	struct wlr_drm_format *format = output_pick_format(output, display_formats,
+		DRM_FORMAT_ARGB8888);
+	if (format == NULL) {
+		format = output_pick_format(output, display_formats,
+			DRM_FORMAT_XRGB8888);
+	}
+	return format;
 }
 
 static struct wlr_buffer *render_cursor_buffer(struct wlr_output_cursor *cursor) {

types/output/render.c

@@ -66,7 +66,12 @@ static bool output_create_swapchain(struct wlr_output *output,
 		}
 	}
 
-	struct wlr_drm_format *format = output_pick_format(output, display_formats);
+	struct wlr_drm_format *format = output_pick_format(output, display_formats,
+		DRM_FORMAT_ARGB8888);
+	if (format == NULL) {
+		format = output_pick_format(output, display_formats,
+			DRM_FORMAT_XRGB8888);
+	}
 	if (format == NULL) {
 		wlr_log(WLR_ERROR, "Failed to pick primary buffer format for output '%s'",
 			output->name);
@@ -231,7 +236,8 @@ void wlr_output_lock_attach_render(struct wlr_output *output, bool lock) {
 }
 
 struct wlr_drm_format *output_pick_format(struct wlr_output *output,
-		const struct wlr_drm_format_set *display_formats) {
+		const struct wlr_drm_format_set *display_formats,
+		uint32_t fmt) {
 	struct wlr_renderer *renderer = output->renderer;
 	struct wlr_allocator *allocator = output->allocator;
 	assert(renderer != NULL && allocator != NULL);
@@ -243,24 +249,20 @@ struct wlr_drm_format *output_pick_format(struct wlr_output *output,
 		return NULL;
 	}
 
-	struct wlr_drm_format *format = NULL;
-	const uint32_t candidates[] = { DRM_FORMAT_ARGB8888, DRM_FORMAT_XRGB8888 };
-	for (size_t i = 0; i < sizeof(candidates) / sizeof(candidates[0]); i++) {
-		uint32_t fmt = candidates[i];
-
 	const struct wlr_drm_format *render_format =
 		wlr_drm_format_set_get(render_formats, fmt);
 	if (render_format == NULL) {
 		wlr_log(WLR_DEBUG, "Renderer doesn't support format 0x%"PRIX32, fmt);
-			continue;
+		return NULL;
 	}
 
+	struct wlr_drm_format *format = NULL;
 	if (display_formats != NULL) {
 		const struct wlr_drm_format *display_format =
 			wlr_drm_format_set_get(display_formats, fmt);
 		if (display_format == NULL) {
 			wlr_log(WLR_DEBUG, "Output doesn't support format 0x%"PRIX32, fmt);
-				continue;
+			return NULL;
 		}
 		format = wlr_drm_format_intersect(display_format, render_format);
 	} else {
@@ -270,14 +272,8 @@ struct wlr_drm_format *output_pick_format(struct wlr_output *output,
 
 	if (format == NULL) {
 		wlr_log(WLR_DEBUG, "Failed to intersect display and render "
-				"modifiers for format 0x%"PRIX32, fmt);
-		} else {
-			break;
-		}
-	}
-	if (format == NULL) {
-		wlr_log(WLR_ERROR, "Failed to choose a format for output '%s'",
-			output->name);
+			"modifiers for format 0x%"PRIX32 " on output '%s",
+			fmt, output->name);
 		return NULL;
 	}