Fix T97380 EEVEE: Weird motion-blur on curves

This was caused by the `mb_data->obmat[]` being wrong because they are
now shared between the particle system and the object.
But Hair need the dupli parent matrix instead of the object matrix.
Disabling `Show Emitter` option fixes the bug.

To avoid this problem, request a different `EEVEE_ObjectMotionData`
for particle systems using a different key pointer in the hash.
This is a bit dirty but there is less code polution using this workaround.

Differential Revision: https://developer.blender.org/D14911

3 files changed, 20 insertions, 9 deletions

diff --git a/source/blender/draw/engines/eevee/eevee_data.c b/source/blender/draw/engines/eevee/eevee_data.c
index 0c56b67ca99..1a1e3b80bad 100644
--- a/source/blender/draw/engines/eevee/eevee_data.c
+++ b/source/blender/draw/engines/eevee/eevee_data.c
@@ -114,7 +114,9 @@ void EEVEE_motion_blur_data_free(EEVEE_MotionBlurData *mb)
   }
 }
 
-EEVEE_ObjectMotionData *EEVEE_motion_blur_object_data_get(EEVEE_MotionBlurData *mb, Object *ob)
+EEVEE_ObjectMotionData *EEVEE_motion_blur_object_data_get(EEVEE_MotionBlurData *mb,
+                                                          Object *ob,
+                                                          bool is_psys)
 {
   if (mb->object == NULL) {
     return NULL;
@@ -123,14 +125,16 @@ EEVEE_ObjectMotionData *EEVEE_motion_blur_object_data_get(EEVEE_MotionBlurData *
   EEVEE_ObjectKey key, *key_p;
   /* Assumes that all instances have the same object pointer. This is currently the case because
    * instance objects are temporary objects on the stack. */
-  key.ob = ob;
+  /* WORKAROUND: Duplicate object key for particle system (hairs) to be able to store dupli offset
+   * matrix along with the emitter obmat. (see T97380) */
+  key.ob = (void *)((char *)ob + is_psys);
   DupliObject *dup = DRW_object_get_dupli(ob);
   if (dup) {
     key.parent = DRW_object_get_dupli_parent(ob);
     memcpy(key.id, dup->persistent_id, sizeof(key.id));
   }
   else {
-    key.parent = key.ob;
+    key.parent = ob;
     memset(key.id, 0, sizeof(key.id));
   }
 
diff --git a/source/blender/draw/engines/eevee/eevee_motion_blur.c b/source/blender/draw/engines/eevee/eevee_motion_blur.c
index 2e0937dbe49..a3ca19c88e1 100644
--- a/source/blender/draw/engines/eevee/eevee_motion_blur.c
+++ b/source/blender/draw/engines/eevee/eevee_motion_blur.c
@@ -226,7 +226,8 @@ void EEVEE_motion_blur_hair_cache_populate(EEVEE_ViewLayerData *UNUSED(sldata),
   }
 
   /* For now we assume hair objects are always moving. */
-  EEVEE_ObjectMotionData *mb_data = EEVEE_motion_blur_object_data_get(&effects->motion_blur, ob);
+  EEVEE_ObjectMotionData *mb_data = EEVEE_motion_blur_object_data_get(
+      &effects->motion_blur, ob, true);
 
   if (mb_data) {
     int mb_step = effects->motion_blur_step;
@@ -283,7 +284,8 @@ void EEVEE_motion_blur_curves_cache_populate(EEVEE_ViewLayerData *UNUSED(sldata)
   }
 
   /* For now we assume curves objects are always moving. */
-  EEVEE_ObjectMotionData *mb_data = EEVEE_motion_blur_object_data_get(&effects->motion_blur, ob);
+  EEVEE_ObjectMotionData *mb_data = EEVEE_motion_blur_object_data_get(
+      &effects->motion_blur, ob, false);
   if (mb_data == NULL) {
     return;
   }
@@ -354,7 +356,8 @@ void EEVEE_motion_blur_cache_populate(EEVEE_ViewLayerData *UNUSED(sldata),
     return;
   }
 
-  EEVEE_ObjectMotionData *mb_data = EEVEE_motion_blur_object_data_get(&effects->motion_blur, ob);
+  EEVEE_ObjectMotionData *mb_data = EEVEE_motion_blur_object_data_get(
+      &effects->motion_blur, ob, false);
 
   if (mb_data) {
     int mb_step = effects->motion_blur_step;
diff --git a/source/blender/draw/engines/eevee/eevee_private.h b/source/blender/draw/engines/eevee/eevee_private.h
index 6128556d364..b03a4fa70b4 100644
--- a/source/blender/draw/engines/eevee/eevee_private.h
+++ b/source/blender/draw/engines/eevee/eevee_private.h
@@ -644,8 +644,10 @@ typedef struct EEVEE_MotionBlurData {
 } EEVEE_MotionBlurData;
 
 typedef struct EEVEE_ObjectKey {
-  /** Object or source object for duplis */
-  struct Object *ob;
+  /** Object or source object for duplis. */
+  /** WORKAROUND: The pointer is different for particle systems and do not point to the real
+   * object. (See T97380) */
+  void *ob;
   /** Parent object for duplis */
   struct Object *parent;
   /** Dupli objects recursive unique identifier */
@@ -1093,7 +1095,9 @@ EEVEE_ViewLayerData *EEVEE_view_layer_data_ensure_ex(struct ViewLayer *view_laye
 EEVEE_ViewLayerData *EEVEE_view_layer_data_ensure(void);
 EEVEE_ObjectEngineData *EEVEE_object_data_get(Object *ob);
 EEVEE_ObjectEngineData *EEVEE_object_data_ensure(Object *ob);
-EEVEE_ObjectMotionData *EEVEE_motion_blur_object_data_get(EEVEE_MotionBlurData *mb, Object *ob);
+EEVEE_ObjectMotionData *EEVEE_motion_blur_object_data_get(EEVEE_MotionBlurData *mb,
+                                                          Object *ob,
+                                                          bool is_psys);
 EEVEE_GeometryMotionData *EEVEE_motion_blur_geometry_data_get(EEVEE_ObjectMotionData *mb_data);
 EEVEE_HairMotionData *EEVEE_motion_blur_hair_data_get(EEVEE_ObjectMotionData *mb_data, Object *ob);
 EEVEE_HairMotionData *EEVEE_motion_blur_curves_data_get(EEVEE_ObjectMotionData *mb_data);