Fix #34485 sculpt strength weirdly inverted with some mesh part.

The view vector was not being calculated correctly. Shamelessly rip off
correct transform to object space from projective texture painting code.

1 files changed, 9 insertions, 7 deletions

diff --git a/source/blender/editors/sculpt_paint/sculpt.c b/source/blender/editors/sculpt_paint/sculpt.c
index 2edd00c015d..8ab71ff5ddc 100644
--- a/source/blender/editors/sculpt_paint/sculpt.c
+++ b/source/blender/editors/sculpt_paint/sculpt.c
@@ -3716,7 +3716,8 @@ static void sculpt_update_cache_invariants(bContext *C, Sculpt *sd, SculptSessio
 	Brush *brush = BKE_paint_brush(&sd->paint);
 	ViewContext *vc = paint_stroke_view_context(op->customdata);
 	Object *ob = CTX_data_active_object(C);
-	float rot[3][3], scale[3], loc[3];
+	float mat[3][3];
+	float viewDir[3] = {0.0f, 0.0f, 1.0f};
 	int i;
 	int mode;
 
@@ -3784,12 +3785,13 @@ static void sculpt_update_cache_invariants(bContext *C, Sculpt *sd, SculptSessio
 	/* cache projection matrix */
 	ED_view3d_ob_project_mat_get(cache->vc->rv3d, ob, cache->projection_mat);
 
-	mat4_to_loc_rot_size(loc, rot, scale, ob->obmat);
-	/* transposing an orthonormal matrix inverts */
-	transpose_m3(rot);
-	ED_view3d_global_to_vector(cache->vc->rv3d, cache->vc->rv3d->twmat[3], cache->true_view_normal);
-	/* This takes care of rotated mesh. Instead of rotating every normal, we inverse rotate view normal. */
-	mul_m3_v3(rot, cache->true_view_normal);
+	invert_m4_m4(ob->imat, ob->obmat);
+	copy_m3_m4(mat, cache->vc->rv3d->viewinv);
+	mul_m3_v3(mat, viewDir);
+	copy_m3_m4(mat, ob->imat);
+	mul_m3_v3(mat, viewDir);
+	normalize_v3_v3(cache->true_view_normal, viewDir);
+
 	/* Initialize layer brush displacements and persistent coords */
 	if (brush->sculpt_tool == SCULPT_TOOL_LAYER) {
 		/* not supported yet for multires or dynamic topology */