compositor: triangle fan debug

Draw the borders of all the triangles.

v1: original
v2: add keybinding to enable/disable fan debug (super-alt-space),
    cycle colors to make it easier to see individual draws, and
    redraw undamaged region to clean up previous frames debug
    lines

Signed-off-by: Rob Clark <rob@ti.com>
diff --git a/src/compositor.h b/src/compositor.h
index 4cdb9e4..96a0477 100644
--- a/src/compositor.h
+++ b/src/compositor.h
@@ -177,7 +177,7 @@
 	struct wl_list mode_list;
 
 	void (*repaint)(struct weston_output *output,
-			pixman_region32_t *damage);
+			pixman_region32_t *damage, int flip);
 	void (*destroy)(struct weston_output *output);
 	void (*assign_planes)(struct weston_output *output);
 	int (*switch_mode)(struct weston_output *output, struct weston_mode *mode);
@@ -322,6 +322,7 @@
 	struct wl_array indices; /* only used in compositor-wayland */
 	struct wl_array vtxcnt;
 	struct weston_plane primary_plane;
+	int fan_debug;
 
 	uint32_t focus;