Fix T32214: Wireframe edge select fails with verts behind the view

This resolves a long standing bug in edge selection
(picking, circle, box & lasso).

Now when one of the edges vertices fails to project into screen space,
the edge is clipped by the viewport to calculate an on-screen location
that can be used instead.

This isn't default as it may be important for the on the screen location
not to be clipped by the viewport.

1 files changed, 24 insertions, 5 deletions

diff --git a/source/blender/editors/space_view3d/view3d_select.c b/source/blender/editors/space_view3d/view3d_select.c
index 6a7ee46f719..5bdeb2cb35f 100644
--- a/source/blender/editors/space_view3d/view3d_select.c
+++ b/source/blender/editors/space_view3d/view3d_select.c
@@ -876,11 +876,16 @@ static bool do_lasso_select_mesh(ViewContext *vc,
 
     const eV3DProjTest clip_flag = V3D_PROJ_TEST_CLIP_NEAR |
                                    (use_zbuf ? 0 : V3D_PROJ_TEST_CLIP_BB);
+    /* Fully inside. */
     mesh_foreachScreenEdge_clip_bb_segment(
         vc, do_lasso_select_mesh__doSelectEdge_pass0, &data_for_edge, clip_flag);
     if (data.is_done == false) {
-      mesh_foreachScreenEdge_clip_bb_segment(
-          vc, do_lasso_select_mesh__doSelectEdge_pass1, &data_for_edge, clip_flag);
+      /* Fall back to partially inside.
+       * Clip content to account for edges partially behind the view. */
+      mesh_foreachScreenEdge_clip_bb_segment(vc,
+                                             do_lasso_select_mesh__doSelectEdge_pass1,
+                                             &data_for_edge,
+                                             clip_flag | V3D_PROJ_TEST_CLIP_CONTENT_DEFAULT);
     }
   }
 
@@ -3071,6 +3076,9 @@ struct BoxSelectUserData_ForMeshEdge {
   struct EditSelectBuf_Cache *esel;
   uint backbuf_offset;
 };
+/**
+ * Pass 0 operates on edges when fully inside.
+ */
 static void do_mesh_box_select__doSelectEdge_pass0(
     void *userData, BMEdge *eed, const float screen_co_a[2], const float screen_co_b[2], int index)
 {
@@ -3092,6 +3100,9 @@ static void do_mesh_box_select__doSelectEdge_pass0(
     data->is_changed = true;
   }
 }
+/**
+ * Pass 1 operates on edges when partially inside.
+ */
 static void do_mesh_box_select__doSelectEdge_pass1(
     void *userData, BMEdge *eed, const float screen_co_a[2], const float screen_co_b[2], int index)
 {
@@ -3181,11 +3192,16 @@ static bool do_mesh_box_select(ViewContext *vc,
 
     const eV3DProjTest clip_flag = V3D_PROJ_TEST_CLIP_NEAR |
                                    (use_zbuf ? 0 : V3D_PROJ_TEST_CLIP_BB);
+    /* Fully inside. */
     mesh_foreachScreenEdge_clip_bb_segment(
         vc, do_mesh_box_select__doSelectEdge_pass0, &cb_data, clip_flag);
     if (data.is_done == false) {
-      mesh_foreachScreenEdge_clip_bb_segment(
-          vc, do_mesh_box_select__doSelectEdge_pass1, &cb_data, clip_flag);
+      /* Fall back to partially inside.
+       * Clip content to account for edges partially behind the view. */
+      mesh_foreachScreenEdge_clip_bb_segment(vc,
+                                             do_mesh_box_select__doSelectEdge_pass1,
+                                             &cb_data,
+                                             clip_flag | V3D_PROJ_TEST_CLIP_CONTENT_DEFAULT);
     }
   }
 
@@ -3774,7 +3790,10 @@ static bool mesh_circle_select(ViewContext *vc,
     }
     else {
       mesh_foreachScreenEdge_clip_bb_segment(
-          vc, mesh_circle_doSelectEdge, &data, V3D_PROJ_TEST_CLIP_NEAR | V3D_PROJ_TEST_CLIP_BB);
+          vc,
+          mesh_circle_doSelectEdge,
+          &data,
+          (V3D_PROJ_TEST_CLIP_NEAR | V3D_PROJ_TEST_CLIP_BB | V3D_PROJ_TEST_CLIP_CONTENT_DEFAULT));
     }
   }