Fix T100700: Compositor crashes when disabled then enabled

The viewport compositor crashes when it is disabled then enabled after
the compositor node tree is edited.

This happens because the compositor engine uses the view_update callback
of the draw engine type to detect changes in the node tree and reset its
state for future evaluation. However, the draw manager only calls the
view_update callback for enabled engines, so the compositor never
receives the needed updates to properly reset its state and then crashes
at draw time.

This patch call the view_update callback for all registered engines
regardless if they are enabled or not, that way, they always receive
the potentially important updated needed to maintain a correct state.

Aside from the compositor engine, this change affects the EEVEE and
Workbench engines because they are the only engines that utilizes this
callback. However, both of them only reset a flag that is checked at
draw time. So the change should have no side effects. For the EEVEE
engine, we just add a null check in case it was not instanced, while
Workbench already have the appropriate null check.

Differential Revision: https://developer.blender.org/D15821

Reviewed By: Clement Foucault

source/blender/draw/engines/eevee/eevee_engine.c

@@ -366,7 +366,7 @@ static void eevee_draw_scene(void *vedata)
 static void eevee_view_update(void *vedata)
 {
   EEVEE_StorageList *stl = ((EEVEE_Data *)vedata)->stl;
-  if (stl->g_data) {
+  if (stl && stl->g_data) {
     stl->g_data->view_updated = true;
   }
 }

source/blender/draw/intern/draw_manager.c

@@ -1344,11 +1344,7 @@ void DRW_notify_view_update(const DRWUpdateContext *update_ctx)
     drw_engines_enable(view_layer, engine_type, gpencil_engine_needed);
     drw_engines_data_validate();
 
-    DRW_ENABLED_ENGINE_ITER (DST.view_data_active, draw_engine, data) {
-      if (draw_engine->view_update) {
-        draw_engine->view_update(data);
-      }
-    }
+    DRW_view_data_engines_view_update(DST.view_data_active);
 
     drw_engines_disable();
   }
@@ -1400,11 +1396,7 @@ static void drw_notify_view_update_offscreen(struct Depsgraph *depsgraph,
       drw_engines_enable(view_layer, engine_type, gpencil_engine_needed);
       drw_engines_data_validate();
 
-      DRW_ENABLED_ENGINE_ITER (DST.view_data_active, draw_engine, data) {
-        if (draw_engine->view_update) {
-          draw_engine->view_update(data);
-        }
-      }
+      DRW_view_data_engines_view_update(DST.view_data_active);
 
       drw_engines_disable();
     }

source/blender/draw/intern/draw_view_data.cc

@@ -197,6 +197,16 @@ void DRW_view_data_free_unused(DRWViewData *view_data)
   }
 }
 
+void DRW_view_data_engines_view_update(DRWViewData *view_data)
+{
+  for (ViewportEngineData &engine_data : view_data->engines) {
+    DrawEngineType *draw_engine = engine_data.engine_type->draw_engine;
+    if (draw_engine->view_update) {
+      draw_engine->view_update(&engine_data);
+    }
+  }
+}
+
 double *DRW_view_data_cache_time_get(DRWViewData *view_data)
 {
   return &view_data->cache_time;

source/blender/draw/intern/draw_view_data.h

@@ -107,6 +107,7 @@ ViewportEngineData *DRW_view_data_engine_data_get_ensure(DRWViewData *view_data,
 void DRW_view_data_use_engine(DRWViewData *view_data, struct DrawEngineType *engine_type);
 void DRW_view_data_reset(DRWViewData *view_data);
 void DRW_view_data_free_unused(DRWViewData *view_data);
+void DRW_view_data_engines_view_update(DRWViewData *view_data);
 double *DRW_view_data_cache_time_get(DRWViewData *view_data);
 DefaultFramebufferList *DRW_view_data_default_framebuffer_list_get(DRWViewData *view_data);
 DefaultTextureList *DRW_view_data_default_texture_list_get(DRWViewData *view_data);