Move rendering related functions out of compton.c

Moved:
* Blur kernel related functions to kernel.c
* Vsync related functions to vsync.c
* paint related functions to render.c

This will make the `split-backend` branch easier to rebase.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/win.h

@@ -16,17 +16,11 @@
 #include "x.h"
 #include "types.h"
 #include "c2.h"
+#include "render.h"
 
 typedef struct session session_t;
 typedef struct _glx_texture glx_texture_t;
 
-// FIXME not the best place for this type
-typedef struct {
-  xcb_pixmap_t pixmap;
-  xcb_render_picture_t pict;
-  glx_texture_t *ptex;
-} paint_t;
-
 #ifdef CONFIG_OPENGL
 // FIXME this type should be in opengl.h
 //       it is very unideal for it to be here
@@ -335,6 +329,24 @@ void
 win_update_frame_extents(session_t *ps, win *w, Window client);
 bool add_win(session_t *ps, Window id, Window prev);
 
+/**
+ * Set fade callback of a window, and possibly execute the previous
+ * callback.
+ *
+ * If a callback can cause rendering result to change, it should call
+ * `queue_redraw`.
+ *
+ * @param exec_callback whether the previous callback is to be executed
+ */
+void win_set_fade_callback(session_t *ps, win **_w,
+    void (*callback) (session_t *ps, win **w), bool exec_callback);
+
+/**
+ * Execute fade callback of a window if fading finished.
+ */
+void
+win_check_fade_finished(session_t *ps, win **_w);
+
 // Stop receiving events (except ConfigureNotify, XXX why?) from a window
 void win_ev_stop(session_t *ps, win *w);