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.

3 files changed, 41 insertions, 10 deletions

diff --git a/source/blender/editors/interface/interface_icons.c b/source/blender/editors/interface/interface_icons.c
index c0360d9b0a7..3d22a26f34b 100644
--- a/source/blender/editors/interface/interface_icons.c
+++ b/source/blender/editors/interface/interface_icons.c
@@ -851,12 +851,15 @@ void ui_icon_ensure_deferred(const bContext *C, const int icon_id, const bool bi
 				{
 					ID *id = (icon->type != 0) ? icon->obj : NULL;
 					PreviewImage *prv = id ? BKE_previewimg_id_ensure(id) : icon->obj;
+					/* Using jobs for screen previews crashes due to offscreen rendering.
+					 * XXX would be nicer if PreviewImage could store if it supports jobs */
+					const bool use_jobs = !id || (GS(id->name) != ID_SCR);
 
 					if (prv) {
 						const int size = big ? ICON_SIZE_PREVIEW : ICON_SIZE_ICON;
 
 						if (id || (prv->tag & PRV_TAG_DEFFERED) != 0) {
-							ui_id_preview_image_render_size(C, NULL, id, prv, size, true);
+							ui_id_preview_image_render_size(C, NULL, id, prv, size, use_jobs);
 						}
 					}
 					break;
@@ -1169,7 +1172,7 @@ void UI_id_icon_render(const bContext *C, Scene *scene, ID *id, const bool big,
 	}
 }
 
-static void ui_id_brush_render(const bContext *C, ID *id)
+static void ui_id_icon_render(const bContext *C, ID *id, bool use_jobs)
 {
 	PreviewImage *pi = BKE_previewimg_id_ensure(id);
 	enum eIconSizes i;
@@ -1181,7 +1184,7 @@ static void ui_id_brush_render(const bContext *C, ID *id)
 		/* check if rect needs to be created; changed
 		 * only set by dynamic icons */
 		if (((pi->flag[i] & PRV_CHANGED) || !pi->rect[i])) {
-			icon_set_image(C, NULL, id, pi, i, true);
+			icon_set_image(C, NULL, id, pi, i, use_jobs);
 			pi->flag[i] &= ~PRV_CHANGED;
 		}
 	}
@@ -1194,7 +1197,7 @@ static int ui_id_brush_get_icon(const bContext *C, ID *id)
 
 	if (br->flag & BRUSH_CUSTOM_ICON) {
 		BKE_icon_id_ensure(id);
-		ui_id_brush_render(C, id);
+		ui_id_icon_render(C, id, true);
 	}
 	else {
 		Object *ob = CTX_data_active_object(C);
@@ -1241,6 +1244,15 @@ static int ui_id_brush_get_icon(const bContext *C, ID *id)
 	return id->icon_id;
 }
 
+static int ui_id_screen_get_icon(const bContext *C, ID *id)
+{
+	BKE_icon_id_ensure(id);
+	/* Don't use jobs here, offscreen rendering doesn't like this and crashes. */
+	ui_id_icon_render(C, id, false);
+
+	return id->icon_id;
+}
+
 int ui_id_icon_get(const bContext *C, ID *id, const bool big)
 {
 	int iconid = 0;
@@ -1259,6 +1271,9 @@ int ui_id_icon_get(const bContext *C, ID *id, const bool big)
 			/* checks if not exists, or changed */
 			UI_id_icon_render(C, NULL, id, big, true);
 			break;
+		case ID_SCR:
+			iconid = ui_id_screen_get_icon(C, id);
+			break;
 		default:
 			break;
 	}
diff --git a/source/blender/editors/interface/interface_regions.c b/source/blender/editors/interface/interface_regions.c
index 466978272bc..62bab15dfb3 100644
--- a/source/blender/editors/interface/interface_regions.c
+++ b/source/blender/editors/interface/interface_regions.c
@@ -1059,7 +1059,7 @@ int ui_searchbox_autocomplete(bContext *C, ARegion *ar, uiBut *but, char *str)
 	return match;
 }
 
-static void ui_searchbox_region_draw_cb(const bContext *UNUSED(C), ARegion *ar)
+static void ui_searchbox_region_draw_cb(const bContext *C, ARegion *ar)
 {
 	uiSearchboxData *data = ar->regiondata;
 	
@@ -1077,6 +1077,9 @@ static void ui_searchbox_region_draw_cb(const bContext *UNUSED(C), ARegion *ar)
 		if (data->preview) {
 			/* draw items */
 			for (a = 0; a < data->items.totitem; a++) {
+				/* ensure icon is up-to-date */
+				ui_icon_ensure_deferred(C, data->items.icons[a], data->preview);
+
 				ui_searchbox_butrect(&rect, data, a);
 				
 				/* widget itself */
diff --git a/source/blender/editors/interface/interface_templates.c b/source/blender/editors/interface/interface_templates.c
index 80784e86b1e..9527ddc7088 100644
--- a/source/blender/editors/interface/interface_templates.c
+++ b/source/blender/editors/interface/interface_templates.c
@@ -415,17 +415,30 @@ static void template_ID(
 		type = idptr.type;
 
 	if (flag & UI_ID_PREVIEWS) {
+		ARegion *region = CTX_wm_region(C);
+		const bool use_big_size = (region->regiontype != RGN_TYPE_HEADER); /* silly check, could be more generic */
+		/* Ugly exception for screens here, drawing their preview in icon size looks ugly/useless */
+		const bool use_preview_icon = use_big_size || (id && (GS(id->name) != ID_SCR));
+		const short width = UI_UNIT_X * (use_big_size ? 6 : 1.6f);
+		const short height = UI_UNIT_Y * (use_big_size ? 6: 1);
+
 		template->preview = true;
 
-		but = uiDefBlockButN(block, id_search_menu, MEM_dupallocN(template), "", 0, 0, UI_UNIT_X * 6, UI_UNIT_Y * 6,
+		but = uiDefBlockButN(block, id_search_menu, MEM_dupallocN(template), "", 0, 0, width, height,
 		                     TIP_(template_id_browse_tip(type)));
-		ui_def_but_icon(but, id ? ui_id_icon_get(C, id, true) : RNA_struct_ui_icon(type),
-		                UI_HAS_ICON | UI_BUT_ICON_PREVIEW);
+		if (use_preview_icon) {
+			ui_def_but_icon(but, ui_id_icon_get(C, id, use_big_size), UI_HAS_ICON | UI_BUT_ICON_PREVIEW);
+		}
+		else {
+			ui_def_but_icon(but, RNA_struct_ui_icon(type), UI_HAS_ICON);
+			UI_but_drawflag_enable(but, UI_BUT_ICON_LEFT);
+		}
 
 		if ((idfrom && idfrom->lib) || !editable)
 			UI_but_flag_enable(but, UI_BUT_DISABLED);
-		
-		uiLayoutRow(layout, true);
+		if (use_big_size) {
+			uiLayoutRow(layout, true);
+		}
 	}
 	else if (flag & UI_ID_BROWSE) {
 		but = uiDefBlockButN(block, id_search_menu, MEM_dupallocN(template), "", 0, 0, UI_UNIT_X * 1.6, UI_UNIT_Y,