UI: Add angle snapping to line gesture tools

This adds support for snapping for line gesture tool. It is implemented
in the modal keymap as Snap, which is a toggle (similar to how snapping
in the transform operator works).

Right now it snaps the angle of the line to 15 degree increments, which
is defined in code. This should be easy to expose in the UI in the future
if we need to.

Reviewed By: Severin

Differential Revision: https://developer.blender.org/D9115

1 files changed, 42 insertions, 0 deletions

diff --git a/source/blender/windowmanager/intern/wm_gesture_ops.c b/source/blender/windowmanager/intern/wm_gesture_ops.c
index faafd6c8235..669cf48a4f2 100644
--- a/source/blender/windowmanager/intern/wm_gesture_ops.c
+++ b/source/blender/windowmanager/intern/wm_gesture_ops.c
@@ -884,6 +884,32 @@ int WM_gesture_straightline_active_side_invoke(bContext *C, wmOperator *op, cons
   return OPERATOR_RUNNING_MODAL;
 }
 
+#define STRAIGHTLINE_SNAP_DEG 15.0f
+static void wm_gesture_straightline_do_angle_snap(rcti *rect)
+{
+  const float line_start[2] = {rect->xmin, rect->ymin};
+  const float line_end[2] = {rect->xmax, rect->ymax};
+  const float x_axis[2] = {1.0f, 0.0f};
+
+  float line_direction[2];
+  sub_v2_v2v2(line_direction, line_end, line_start);
+  const float line_length = normalize_v2(line_direction);
+
+  const float angle = angle_signed_v2v2(x_axis, line_direction);
+  const float angle_deg = RAD2DEG(angle) + (STRAIGHTLINE_SNAP_DEG / 2.0f);
+  const float angle_snapped_deg = -floorf(angle_deg / STRAIGHTLINE_SNAP_DEG) *
+                                  STRAIGHTLINE_SNAP_DEG;
+  const float angle_snapped = DEG2RAD(angle_snapped_deg);
+
+  float line_snapped_end[2];
+  rotate_v2_v2fl(line_snapped_end, x_axis, angle_snapped);
+  mul_v2_fl(line_snapped_end, line_length);
+  add_v2_v2(line_snapped_end, line_start);
+
+  rect->xmax = (int)line_snapped_end[0];
+  rect->ymax = (int)line_snapped_end[1];
+}
+
 /**
  * This modal callback calls exec once per mouse move event while the gesture is active with the
  * updated line start and end values, so it can be used for tools that have a real time preview
@@ -912,6 +938,10 @@ int WM_gesture_straightline_modal(bContext *C, wmOperator *op, const wmEvent *ev
       gesture_straightline_apply(C, op);
     }
 
+    if (gesture->use_snap) {
+      wm_gesture_straightline_do_angle_snap(rect);
+    }
+
     wm_gesture_tag_redraw(win);
   }
   else if (event->type == EVT_MODAL_MAP) {
@@ -925,6 +955,10 @@ int WM_gesture_straightline_modal(bContext *C, wmOperator *op, const wmEvent *ev
           wm_gesture_tag_redraw(win);
         }
         break;
+      case GESTURE_MODAL_SNAP:
+        /* Toggle snapping on/off. */
+        gesture->use_snap = !gesture->use_snap;
+        break;
       case GESTURE_MODAL_SELECT:
         if (gesture_straightline_apply(C, op)) {
           gesture_modal_end(C, op);
@@ -971,6 +1005,10 @@ int WM_gesture_straightline_oneshot_modal(bContext *C, wmOperator *op, const wmE
       rect->ymax = event->y - gesture->winrct.ymin;
     }
 
+    if (gesture->use_snap) {
+      wm_gesture_straightline_do_angle_snap(rect);
+    }
+
     wm_gesture_tag_redraw(win);
   }
   else if (event->type == EVT_MODAL_MAP) {
@@ -984,6 +1022,10 @@ int WM_gesture_straightline_oneshot_modal(bContext *C, wmOperator *op, const wmE
           wm_gesture_tag_redraw(win);
         }
         break;
+      case GESTURE_MODAL_SNAP:
+        /* Toggle snapping on/off. */
+        gesture->use_snap = !gesture->use_snap;
+        break;
       case GESTURE_MODAL_SELECT:
       case GESTURE_MODAL_DESELECT:
       case GESTURE_MODAL_IN: