Improves the accuracy of snap to edges

Recently the snap to edges has been changed to work with coordinates 2d. Thus, the lambda of the snap pointon on edge becomes different from the actual lambda in a 3d edge.

The solution to correct the lambda was this:

```
if (is_persp) {
	const float fac = depth_a / (depth_a + depth_b);
	lambda *= (1.0f + (fac - 0.5f) * (1.0f - lambda));
````

...
But the lambda was still not very accurate.
Now the function uses the `dist_squared_ray_to_seg_v3` to get the coordinate of the snap point on the edge. And then tests that point.

The accuracy returned to normal values.

1 files changed, 32 insertions, 92 deletions

diff --git a/source/blender/editors/transform/transform_snap_object.c b/source/blender/editors/transform/transform_snap_object.c
index 36a064e6265..29ac8f88fed 100644
--- a/source/blender/editors/transform/transform_snap_object.c
+++ b/source/blender/editors/transform/transform_snap_object.c
@@ -454,85 +454,14 @@ static bool test_projected_vert_dist(
 
 static bool test_projected_edge_dist(
         PreDefProject *projectdefs,
-        const float va[3], const float vb[3], const bool is_persp,
-        const float mval[2], const float depth_range[2],
+        const float va[3], const float vb[3], const float ray_start[3], const float ray_normal[3],
+        const bool is_persp, const float mval[2], const float depth_range[2],
         float r_co[3])
 {
-	float depth_a, depth_b;
-	float(*pmat)[4] = projectdefs->pmat;
-
-	if (is_persp) {
-		depth_a = mul_project_m4_v3_zfac(pmat, va);
-		depth_b = mul_project_m4_v3_zfac(pmat, vb);
-
-		if (depth_a < depth_range[0] && depth_b < depth_range[0]) {
-			return false;
-		}
-	}
-
-	float va2d[2] = {
-		(dot_m4_v3_row_x(pmat, va) + pmat[3][0]),
-		(dot_m4_v3_row_y(pmat, va) + pmat[3][1]),
-	};
-	float vb2d[2] = {
-		(dot_m4_v3_row_x(pmat, vb) + pmat[3][0]),
-		(dot_m4_v3_row_y(pmat, vb) + pmat[3][1]),
-	};
 
-	if (is_persp) {
-		mul_v2_fl(va2d, 1 / depth_a);
-		mul_v2_fl(vb2d, 1 / depth_b);
-	}
-
-	va2d[0] += 1.0f;
-	va2d[1] += 1.0f;
-	vb2d[0] += 1.0f;
-	vb2d[1] += 1.0f;
-
-	va2d[0] *= projectdefs->win_half[0];
-	va2d[1] *= projectdefs->win_half[1];
-	vb2d[0] *= projectdefs->win_half[0];
-	vb2d[1] *= projectdefs->win_half[1];
-
-	float tmp_point[2], edge[2], rdist;
-	sub_v3_v3v3(tmp_point, mval, va2d);
-	sub_v3_v3v3(edge, vb2d, va2d);
-	float lambda = dot_v2v2(tmp_point, edge) / len_squared_v2(edge);
-	if (lambda <= 0) {
-		lambda = 0.0f;
-		//copy_v2_v2(tmp_point, va2d);
-		rdist = len_squared_v2v2(mval, va2d);
-	}
-	else if (lambda >= 1.0f) {
-		lambda = 1.0f;
-		//copy_v2_v2(tmp_point, vb2d);
-		rdist = len_squared_v2v2(mval, vb2d);
-	}
-	else {
-		madd_v2_v2v2fl(tmp_point, va2d, edge, lambda);
-		//madd_v2_v2fl(va2d, edge, lambda);
-		rdist = len_squared_v2v2(mval, tmp_point);
-	}
-	if (rdist < projectdefs->dist_px_sq) {
-		if (r_co) {
-			if (is_persp) {
-				const float fac = depth_a / (depth_a + depth_b);
-				lambda *= (1.0f + (fac - 0.5f) * (1.0f - lambda));
-
-				const float depth = depth_a + (depth_b - depth_a) * lambda;
-				if (depth < depth_range[0] || depth > depth_range[1]) {
-					return false;
-				}
-			}
-			float seg[3];
-			sub_v3_v3v3(seg, vb, va);
-			madd_v3_v3v3fl(r_co, va, seg, lambda);
-		}
-
-		projectdefs->dist_px_sq = rdist;
-		return true;
-	}
-	return false;
+	float tmp_co[3], depth;
+	dist_squared_ray_to_seg_v3(ray_start, ray_normal, va, vb, tmp_co, &depth);
+	return test_projected_vert_dist(projectdefs, tmp_co, is_persp, mval, depth_range, r_co);
 }
 
 /** \} */
@@ -561,7 +490,7 @@ typedef struct Object_Nearest2dPrecalc {
 
 
 static void nearest2d_precalc(
-        struct Object_Nearest2dPrecalc *neasrest_precalc, const ARegion *ar,
+        Object_Nearest2dPrecalc *neasrest_precalc, const ARegion *ar,
         const float dist_px, float obmat[4][4],
         const float ray_origin_local[3], const float ray_direction_local[3],
         const float mval[2], const float depth_range[2])
@@ -776,8 +705,9 @@ static bool cb_leaf_snap_edge(const BVHTreeAxisRange *UNUSED(bounds), int index,
 	get_edge_verts(neasrest_precalc->userdata, index, v_pair);
 
 	if (test_projected_edge_dist(
-	        &neasrest_precalc->projectdefs, v_pair[0], v_pair[1], true,
-	        neasrest_precalc->mval, neasrest_precalc->depth_range,
+	        &neasrest_precalc->projectdefs, v_pair[0], v_pair[1],
+	        neasrest_precalc->ray_origin_local, neasrest_precalc->ray_direction_local,
+	        true, neasrest_precalc->mval, neasrest_precalc->depth_range,
 	        neasrest_precalc->co))
 	{
 		sub_v3_v3v3(neasrest_precalc->no, v_pair[0], v_pair[1]);
@@ -801,8 +731,8 @@ static bool cb_nearest_walk_order(const BVHTreeAxisRange *UNUSED(bounds), char a
 
 static bool snapArmature(
         const ARegion *ar, Object *ob, bArmature *arm, float obmat[4][4],
-        const short snap_to, const float mval[2], const bool is_persp,
-        const float depth_range[2],
+        const short snap_to, const float origin[3], const float dir[3],
+        const float mval[2], const bool is_persp, const float depth_range[2],
         /* read/write args */
         float *dist_px,
         /* return args */
@@ -810,6 +740,17 @@ static bool snapArmature(
 {
 	bool retval = false;
 
+	float ray_start_local[3], ray_normal_local[3];
+	if (snap_to != SCE_SNAP_MODE_VERTEX) {
+		float imat[4][4];
+		invert_m4_m4(imat, obmat);
+
+		copy_v3_v3(ray_start_local, origin);
+		copy_v3_v3(ray_normal_local, dir);
+		mul_m4_v3(imat, ray_start_local);
+		mul_mat3_m4_v3(imat, ray_normal_local);
+	}
+
 	PreDefProject projectdefs;
 	precalc_project(&projectdefs, ar, *dist_px, obmat);
 
@@ -827,8 +768,8 @@ static bool snapArmature(
 							break;
 						case SCE_SNAP_MODE_EDGE:
 							retval |= test_projected_edge_dist(
-							        &projectdefs, eBone->head, eBone->tail, is_persp,
-							        mval, depth_range, r_loc);
+							        &projectdefs, eBone->head, eBone->tail, ray_start_local, ray_normal_local,
+							        is_persp, mval, depth_range, r_loc);
 							break;
 					}
 				}
@@ -852,8 +793,8 @@ static bool snapArmature(
 						break;
 					case SCE_SNAP_MODE_EDGE:
 						retval |= test_projected_edge_dist(
-						        &projectdefs,  head_vec, tail_vec, is_persp,
-						        mval, depth_range, r_loc);
+						        &projectdefs, head_vec, tail_vec, ray_start_local, ray_normal_local,
+						        is_persp, mval, depth_range, r_loc);
 						break;
 				}
 			}
@@ -1323,8 +1264,8 @@ static bool snapDerivedMesh(
 				data.retval = retval;
 
 				BLI_bvhtree_ray_cast_all(
-					    treedata->tree, ray_start_local, ray_normal_local, 0.0f,
-					    *ray_depth, raycast_all_cb, &data);
+				        treedata->tree, ray_start_local, ray_normal_local, 0.0f,
+				        *ray_depth, raycast_all_cb, &data);
 
 				retval = data.retval;
 			}
@@ -1645,8 +1586,8 @@ static bool snapEditMesh(
 				data.retval = retval;
 
 				BLI_bvhtree_ray_cast_all(
-					    treedata->tree, ray_start_local, ray_normal_local, 0.0f,
-					    *ray_depth, raycast_all_cb, &data);
+				        treedata->tree, ray_start_local, ray_normal_local, 0.0f,
+				        *ray_depth, raycast_all_cb, &data);
 
 				retval = data.retval;
 			}
@@ -1828,9 +1769,8 @@ static bool snapObject(
 	else if (snap_to != SCE_SNAP_MODE_FACE) {
 		if (ob->type == OB_ARMATURE) {
 			retval = snapArmature(
-			        ar, ob, ob->data, obmat, snap_to, mval, is_persp,
-			        depth_range,
-			        dist_px,
+			        ar, ob, ob->data, obmat, snap_to, ray_origin, ray_normal,
+			        mval, is_persp, depth_range, dist_px,
 			        r_loc, r_no);
 		}
 		else if (ob->type == OB_CURVE) {