Knife: Preserve right click cancel functionality

Currently, the knife does not use right click cancel.
It causes users to accidentally delete entire cuts easily.

This patch allows right click cancel when no cuts have been made.
This makes it consistent with other tools when switching between them.
More info: https://devtalk.blender.org/t/gsoc-2021-knife-tool-improvements-feedback/19047/175?u=hobbesos

1 files changed, 14 insertions, 0 deletions

diff --git a/source/blender/editors/mesh/editmesh_knife.c b/source/blender/editors/mesh/editmesh_knife.c
index 8e0a7dbd69b..09ae779138c 100644
--- a/source/blender/editors/mesh/editmesh_knife.c
+++ b/source/blender/editors/mesh/editmesh_knife.c
@@ -240,6 +240,7 @@ typedef struct KnifeTool_OpData {
 
   BLI_mempool *kverts;
   BLI_mempool *kedges;
+  bool no_cuts; /* A cut has not been made yet. */
 
   BLI_Stack *undostack;
   BLI_Stack *splitstack; /* Store edge splits by #knife_split_edge. */
@@ -4089,6 +4090,8 @@ static void knifetool_init(bContext *C,
     knife_init_colors(&kcd->colors);
   }
 
+  kcd->no_cuts = true;
+
   kcd->axis_string[0] = ' ';
   kcd->axis_string[1] = '\0';
 
@@ -4501,12 +4504,23 @@ static int knifetool_modal(bContext *C, wmOperator *op, const wmEvent *event)
         handled = true;
         break;
       case KNF_MODAL_NEW_CUT:
+        /* If no cuts have been made, exit.
+         * Preserves right click cancel workflow which most tools use,
+         * but stops accidentally deleting entire cuts with right click.
+         */
+        if (kcd->no_cuts) {
+          ED_region_tag_redraw(kcd->region);
+          knifetool_exit(op);
+          ED_workspace_status_text(C, NULL);
+          return OPERATOR_CANCELLED;
+        }
         ED_region_tag_redraw(kcd->region);
         knife_finish_cut(kcd);
         kcd->mode = MODE_IDLE;
         handled = true;
         break;
       case KNF_MODAL_ADD_CUT:
+        kcd->no_cuts = false;
         knife_recalc_ortho(kcd);
 
         /* Get the value of the event which triggered this one. */