Draw Manager: Add request redraw method.

This is extremly hacky and against notifier design. This must be revisited later.
We might want to mimic external renderer way of requesting redraw.

source/blender/draw/intern/DRW_render.h

@@ -335,6 +335,8 @@ bool DRW_viewport_is_persp_get(void);
 struct DefaultFramebufferList *DRW_viewport_framebuffer_list_get(void);
 struct DefaultTextureList     *DRW_viewport_texture_list_get(void);
 
+void DRW_viewport_request_redraw(void);
+
 /* SceneLayers */
 void **DRW_scene_layer_engine_data_get(DrawEngineType *engine_type, void (*callback)(void *storage));
 

source/blender/draw/intern/draw_manager.c

@@ -75,13 +75,15 @@
 #include "UI_interface.h"
 #include "UI_resources.h"
 
+#include "WM_api.h"
+#include "WM_types.h"
+
 #include "draw_manager_text.h"
 
 /* only for callbacks */
 #include "draw_cache_impl.h"
 
 #include "draw_mode_engines.h"
-
 #include "engines/clay/clay_engine.h"
 #include "engines/eevee/eevee_engine.h"
 #include "engines/basic/basic_engine.h"
@@ -2291,6 +2293,12 @@ DefaultTextureList *DRW_viewport_texture_list_get(void)
 	return GPU_viewport_texture_list_get(DST.viewport);
 }
 
+void DRW_viewport_request_redraw(void)
+{
+	/* XXXXXXXXXXX HAAAAAAAACKKKK */
+	WM_main_add_notifier(NC_MATERIAL | ND_SHADING_DRAW, NULL);
+}
+
 /** \} */