Compositor: add pre/post/cancel handlers and background job info

Main motivation is from T54314 where there was no way to read from a
Viewer image datablock after the compositor has run.
The only solution there was to do a full rerender (which obviously takes
much longer). Adding a handler avoids having to rerender.

This uses new syntax from rBf4456a4d3c97 and also adds "COMPOSITE" as a
job type that can be queried by `bpy.app.is_job_running`.

NOTE: there is another issue when multiple viewers are used and these
get active via RNA (compo execution is not triggered there yet -- unlike
when a viewer is selected in the Editor -- this is an issue of
`ED_node_set_active` vs. only `nodeSetActive`, but this will be tackled
separately)

Maniphest Tasks: T54314

Differential Revision: https://developer.blender.org/D15078

source/blender/blenkernel/BKE_callbacks.h

@@ -100,6 +100,9 @@ typedef enum {
   BKE_CB_EVT_OBJECT_BAKE_PRE,
   BKE_CB_EVT_OBJECT_BAKE_COMPLETE,
   BKE_CB_EVT_OBJECT_BAKE_CANCEL,
+  BKE_CB_EVT_COMPOSITE_PRE,
+  BKE_CB_EVT_COMPOSITE_POST,
+  BKE_CB_EVT_COMPOSITE_CANCEL,
   BKE_CB_EVT_TOT,
 } eCbEvent;
 

source/blender/editors/space_node/node_edit.cc

@@ -15,6 +15,7 @@
 #include "DNA_text_types.h"
 #include "DNA_world_types.h"
 
+#include "BKE_callbacks.h"
 #include "BKE_context.h"
 #include "BKE_global.h"
 #include "BKE_image.h"
@@ -275,6 +276,7 @@ static void compo_startjob(void *cjv,
 
   // XXX BIF_store_spare();
   /* 1 is do_previews */
+  BKE_callback_exec_id(cj->bmain, &scene->id, BKE_CB_EVT_COMPOSITE_PRE);
 
   if ((cj->scene->r.scemode & R_MULTIVIEW) == 0) {
     ntreeCompositExecTree(cj->scene, ntree, &cj->scene->r, false, true, "");
@@ -293,6 +295,22 @@ static void compo_startjob(void *cjv,
   ntree->progress = nullptr;
 }
 
+static void compo_canceljob(void *cjv)
+{
+  CompoJob *cj = (CompoJob *)cjv;
+  Main *bmain = cj->bmain;
+  Scene *scene = cj->scene;
+  BKE_callback_exec_id(bmain, &scene->id, BKE_CB_EVT_COMPOSITE_CANCEL);
+}
+
+static void compo_completejob(void *cjv)
+{
+  CompoJob *cj = (CompoJob *)cjv;
+  Main *bmain = cj->bmain;
+  Scene *scene = cj->scene;
+  BKE_callback_exec_id(bmain, &scene->id, BKE_CB_EVT_COMPOSITE_POST);
+}
+
 /** \} */
 
 }  // namespace blender::ed::space_node
@@ -339,7 +357,13 @@ void ED_node_composite_job(const bContext *C, struct bNodeTree *nodetree, Scene
   /* setup job */
   WM_jobs_customdata_set(wm_job, cj, compo_freejob);
   WM_jobs_timer(wm_job, 0.1, NC_SCENE | ND_COMPO_RESULT, NC_SCENE | ND_COMPO_RESULT);
-  WM_jobs_callbacks(wm_job, compo_startjob, compo_initjob, compo_updatejob, nullptr);
+  WM_jobs_callbacks_ex(wm_job,
+                       compo_startjob,
+                       compo_initjob,
+                       compo_updatejob,
+                       nullptr,
+                       compo_completejob,
+                       compo_canceljob);
 
   WM_jobs_start(CTX_wm_manager(C), wm_job);
 }

source/blender/makesrna/intern/rna_wm.c

@@ -137,6 +137,7 @@ const EnumPropertyItem rna_enum_wm_job_type_items[] = {
     {WM_JOB_TYPE_RENDER, "RENDER", 0, "Regular rendering", ""},
     {WM_JOB_TYPE_RENDER_PREVIEW, "RENDER_PREVIEW", 0, "Rendering previews", ""},
     {WM_JOB_TYPE_OBJECT_BAKE, "OBJECT_BAKE", 0, "Object Baking", ""},
+    {WM_JOB_TYPE_COMPOSITE, "COMPOSITE", 0, "Compositing", ""},
     {0, NULL, 0, NULL, NULL},
 };
 

source/blender/python/intern/bpy_app_handlers.c

@@ -66,10 +66,12 @@ static PyStructSequence_Field app_cb_info_fields[] = {
     {"xr_session_start_pre", "on starting an xr session (before)"},
     {"annotation_pre", "on drawing an annotation (before)"},
     {"annotation_post", "on drawing an annotation (after)"},
-
     {"object_bake_pre", "before starting a bake job"},
     {"object_bake_complete", "on completing a bake job; will be called in the main thread"},
     {"object_bake_cancel", "on canceling a bake job; will be called in the main thread"},
+    {"composite_pre", "on a compositing background job (before)"},
+    {"composite_post", "on a compositing background job (after)"},
+    {"composite_cancel", "on a compositing background job (cancel)"},
 
 /* sets the permanent tag */
 #define APP_CB_OTHER_FIELDS 1