UI: Previews for screen layouts

Basically all this does is drawing layout previews into the opened layout search menu.
https://youtu.be/RHYWtZP7pyA

The previews are drawn using offscreen rendering so they can't use multi-threading (yet!). But that shouldn't be an issue since only a handful of previews are drawn at the same time. Normally we only need to redraw the preview if a screen layout was changed. Would be nice if PreviewImage could store if it supports threaded rendering.
Previews are saved in files, might be useful if you later want to support appending layouts.
Adds a new file screen_draw.c.

1 files changed, 4 insertions, 0 deletions

diff --git a/source/blender/editors/include/ED_screen.h b/source/blender/editors/include/ED_screen.h
index ec09add56b8..f5f66a07aea 100644
--- a/source/blender/editors/include/ED_screen.h
+++ b/source/blender/editors/include/ED_screen.h
@@ -36,6 +36,8 @@
 #include "DNA_view2d_types.h"
 #include "DNA_view3d_types.h"
 
+#include "BLI_compiler_attrs.h"
+
 struct wmWindowManager;
 struct wmWindow;
 struct wmNotifier;
@@ -47,6 +49,7 @@ struct bScreen;
 struct ARegion;
 struct uiBlock;
 struct rcti;
+struct Main;
 
 /* regions */
 void    ED_region_do_listen(struct bScreen *sc, struct ScrArea *sa, struct ARegion *ar, struct wmNotifier *note);
@@ -118,6 +121,7 @@ void    ED_screen_full_restore(struct bContext *C, ScrArea *sa);
 struct ScrArea *ED_screen_state_toggle(struct bContext *C, struct wmWindow *win, struct ScrArea *sa, const short state);
 void    ED_screens_header_tools_menu_create(struct bContext *C, struct uiLayout *layout, void *arg);
 bool    ED_screen_stereo3d_required(struct bScreen *screen);
+void    ED_screen_preview_render(const struct bScreen *screen, int size_x, int size_y, unsigned int *r_rect) ATTR_NONNULL();
 
 /* anim */
 void    ED_update_for_newframe(struct Main *bmain, struct Scene *scene, int mute);