Drawable: Ignore exposes when we have nothing to draw

The X11 server tells us about things that need to be redrawn via expose events.
When we get such an expose event before lua drew the drawable, we just fill the
exposed area with old data (which is black for newly-created drawables).

Fix this by tracking if we have any usable data in a drawable's double buffering
pixmap. This flag is unset whenever we throw away the old content (e.g. due to a
resize) and is set when lua gave us some new content to display.

Signed-off-by: Uli Schlachter <psychon@znc.in>

objects/client.c

@@ -1524,14 +1524,18 @@ client_get_drawable(client_t *c, int x, int y)
 static void
 client_refresh_titlebar_partial(client_t *c, client_titlebar_t bar, int16_t x, int16_t y, uint16_t width, uint16_t height)
 {
-    if(c->titlebar[bar].drawable == NULL || c->titlebar[bar].drawable->pixmap == XCB_NONE)
+    if(c->titlebar[bar].drawable == NULL
+            || c->titlebar[bar].drawable->pixmap == XCB_NONE
+            || !c->titlebar[bar].drawable->refreshed)
         return;
-    area_t area = titlebar_get_area(c, bar);
+
     /* Is the titlebar part of the area that should get redrawn? */
+    area_t area = titlebar_get_area(c, bar);
     if (AREA_LEFT(area) >= x + width || AREA_RIGHT(area) <= x)
         return;
     if (AREA_TOP(area) >= y + height || AREA_BOTTOM(area) <= y)
         return;
+
     /* Redraw the affected parts */
     cairo_surface_flush(c->titlebar[bar].drawable->surface);
     xcb_copy_area(globalconf.connection, c->titlebar[bar].drawable->pixmap, c->frame_window,

objects/drawable.c

@@ -34,6 +34,7 @@ drawable_allocator(lua_State *L, drawable_refresh_callback *callback, void *data
     drawable_t *d = drawable_new(L);
     d->refresh_callback = callback;
     d->refresh_data = data;
+    d->refreshed = false;
     d->surface = NULL;
     d->pixmap = XCB_NONE;
     return d;
@@ -46,6 +47,7 @@ drawable_unset_surface(drawable_t *d)
     cairo_surface_destroy(d->surface);
     if (d->pixmap)
         xcb_free_pixmap(globalconf.connection, d->pixmap);
+    d->refreshed = false;
     d->surface = NULL;
     d->pixmap = XCB_NONE;
 }
@@ -108,6 +110,7 @@ static int
 luaA_drawable_refresh(lua_State *L)
 {
     drawable_t *drawable = luaA_checkudata(L, 1, &drawable_class);
+    drawable->refreshed = true;
     (*drawable->refresh_callback)(drawable->refresh_data);
 
     return 0;

objects/drawable.h

@@ -38,6 +38,8 @@ struct drawable_t
     cairo_surface_t *surface;
     /** The geometry of the drawable (in root window coordinates). */
     area_t geometry;
+    /** Surface contents are undefined if this is false. */
+    bool refreshed;
     /** Callback for refreshing. */
     drawable_refresh_callback *refresh_callback;
     /** Data for refresh callback. */

objects/drawin.c

@@ -177,7 +177,7 @@ drawin_refresh_pixmap_partial(drawin_t *drawin,
                               int16_t x, int16_t y,
                               uint16_t w, uint16_t h)
 {
-    if (!drawin->drawable || !drawin->drawable->pixmap)
+    if (!drawin->drawable || !drawin->drawable->pixmap || !drawin->drawable->refreshed)
         return;
 
     /* Make cairo do all pending drawing */