Fix T94564: Mirror clipping is not properly placed in sculpt mode

If a mirror object is used in a mirror modifier, sculptmode did not take
this into account (and instead always clipped on the sculpt objects
local axis).

Now take this into account by storing a matrix in the preparation
function `sculpt_init_mirror_clipping` and use that later in
`SCULPT_clip`.

Maniphest Tasks: T94564

Differential Revision: https://developer.blender.org/D13711

2 files changed, 27 insertions, 2 deletions

diff --git a/source/blender/editors/sculpt_paint/sculpt.c b/source/blender/editors/sculpt_paint/sculpt.c
index 06b5de9719e..cfa6a492b2b 100644
--- a/source/blender/editors/sculpt_paint/sculpt.c
+++ b/source/blender/editors/sculpt_paint/sculpt.c
@@ -2372,8 +2372,23 @@ void SCULPT_clip(Sculpt *sd, SculptSession *ss, float co[3], const float val[3])
       continue;
     }
 
-    if ((ss->cache->flag & (CLIP_X << i)) && (fabsf(co[i]) <= ss->cache->clip_tolerance[i])) {
-      co[i] = 0.0f;
+    bool do_clip = false;
+    float co_clip[3];
+    if (ss->cache && (ss->cache->flag & (CLIP_X << i))) {
+      /* Take possible mirror object into account. */
+      mul_v3_m4v3(co_clip, ss->cache->clip_mirror_mtx, co);
+
+      if (fabsf(co_clip[i]) <= ss->cache->clip_tolerance[i]) {
+        co_clip[i] = 0.0f;
+        float imtx[4][4];
+        invert_m4_m4(imtx, ss->cache->clip_mirror_mtx);
+        mul_m4_v3(imtx, co_clip);
+        do_clip = true;
+      }
+    }
+
+    if (do_clip) {
+      co[i] = co_clip[i];
     }
     else {
       co[i] = val[i];
@@ -6005,6 +6020,8 @@ static void sculpt_init_mirror_clipping(Object *ob, SculptSession *ss)
 {
   ModifierData *md;
 
+  unit_m4(ss->cache->clip_mirror_mtx);
+
   for (md = ob->modifiers.first; md; md = md->next) {
     if (md->type == eModifierType_Mirror && (md->mode & eModifierMode_Realtime)) {
       MirrorModifierData *mmd = (MirrorModifierData *)md;
@@ -6023,6 +6040,13 @@ static void sculpt_init_mirror_clipping(Object *ob, SculptSession *ss)
           }
         }
       }
+
+      /* Store matrix for mirror object clipping. */
+      if (mmd->mirror_ob) {
+        float imtx_mirror_ob[4][4];
+        invert_m4_m4(imtx_mirror_ob, mmd->mirror_ob->obmat);
+        mul_m4_m4m4(ss->cache->clip_mirror_mtx, imtx_mirror_ob, ob->obmat);
+      }
     }
   }
 }
diff --git a/source/blender/editors/sculpt_paint/sculpt_intern.h b/source/blender/editors/sculpt_paint/sculpt_intern.h
index ec7ea1d85f4..d6616ca6cce 100644
--- a/source/blender/editors/sculpt_paint/sculpt_intern.h
+++ b/source/blender/editors/sculpt_paint/sculpt_intern.h
@@ -691,6 +691,7 @@ typedef struct StrokeCache {
   float scale[3];
   int flag;
   float clip_tolerance[3];
+  float clip_mirror_mtx[4][4];
   float initial_mouse[2];
 
   /* Variants */