Fix T41842: Knife edge-snap, incorrect offset

1 files changed, 25 insertions, 3 deletions

diff --git a/source/blender/editors/mesh/editmesh_knife.c b/source/blender/editors/mesh/editmesh_knife.c
index 165af62c715..30d8918d85c 100644
--- a/source/blender/editors/mesh/editmesh_knife.c
+++ b/source/blender/editors/mesh/editmesh_knife.c
@@ -182,6 +182,7 @@ typedef struct KnifeTool_OpData {
 	BLI_mempool *refs;
 
 	float projmat[4][4];
+	float projmat_inv[4][4];
 
 	KnifeColors colors;
 
@@ -251,6 +252,27 @@ static void knife_project_v2(const KnifeTool_OpData *kcd, const float co[3], flo
 	ED_view3d_project_float_v2_m4(kcd->ar, co, sco, (float (*)[4])kcd->projmat);
 }
 
+/* use when lambda is in screen-space */
+static void knife_interp_v3_v3v3(
+        const KnifeTool_OpData *kcd,
+        float r_co[3], const float v1[3], const float v2[3], float lambda_ss)
+{
+	if (kcd->is_ortho) {
+		interp_v3_v3v3(r_co, v1, v2, lambda_ss);
+	}
+	else {
+		/* transform into screen-space, interp, then transform back */
+		float v1_ss[3], v2_ss[3];
+
+		mul_v3_project_m4_v3(v1_ss, (float (*)[4])kcd->projmat, v1);
+		mul_v3_project_m4_v3(v2_ss, (float (*)[4])kcd->projmat, v2);
+
+		interp_v3_v3v3(r_co, v1_ss, v2_ss, lambda_ss);
+
+		mul_project_m4_v3((float (*)[4])kcd->projmat_inv, r_co);
+	}
+}
+
 static void knife_pos_data_clear(KnifePosData *kpd)
 {
 	zero_v3(kpd->co);
@@ -1682,8 +1704,8 @@ static KnifeEdge *knife_find_closest_edge(KnifeTool_OpData *kcd, float p[3], flo
 				}
 			}
 
-			/* now we have 'lambda' calculated */
-			interp_v3_v3v3(test_cagep, kfe->v1->cageco, kfe->v2->cageco, lambda);
+			/* now we have 'lambda' calculated (in screen-space) */
+			knife_interp_v3_v3v3(kcd, test_cagep, kfe->v1->cageco, kfe->v2->cageco, lambda);
 
 			if (kcd->vc.rv3d->rflag & RV3D_CLIPPING) {
 				/* check we're in the view */
@@ -2597,7 +2619,7 @@ static void knife_recalc_projmat(KnifeTool_OpData *kcd)
 {
 	invert_m4_m4(kcd->ob->imat, kcd->ob->obmat);
 	ED_view3d_ob_project_mat_get(kcd->ar->regiondata, kcd->ob, kcd->projmat);
-	//mul_m4_m4m4(kcd->projmat, kcd->vc.rv3d->winmat, kcd->vc.rv3d->viewmat);
+	invert_m4_m4(kcd->projmat_inv, kcd->projmat);
 
 	kcd->is_ortho = ED_view3d_clip_range_get(kcd->vc.v3d, kcd->vc.rv3d,
 	                                         &kcd->clipsta, &kcd->clipend, true);