Fix T101894: only do FCurve-select if no keys have been touched previously

Change the behaviour of circle select on FCurves:
- Before any key is touched, the behaviour is as it was (key included in
  circle-select area → select it; otherwise → select entire curve)
- If any key has been touched, an internal option
  (`use_curve_selection`) is  flipped and selecting the entire curve is
  disallowed.

This ensures that once a key changes selection state, it's no longer
possible to select the entire curve. This allows dragging over keys and
subsequently drag over a keyless part of the curve.

Reviewed By: RiggingDojo, troopy28

Maniphest Tasks: T101894

Differential Revision: https://developer.blender.org/D16307

1 files changed, 6 insertions, 0 deletions

diff --git a/source/blender/editors/space_graph/graph_select.c b/source/blender/editors/space_graph/graph_select.c
index 932ed417f21..3265dcbf0d1 100644
--- a/source/blender/editors/space_graph/graph_select.c
+++ b/source/blender/editors/space_graph/graph_select.c
@@ -1061,6 +1061,12 @@ static int graph_circle_select_exec(bContext *C, wmOperator *op)
   /* Apply box_select action. */
   const bool any_key_selection_changed = box_select_graphkeys(
       &ac, &rect_fl, BEZT_OK_REGION_CIRCLE, selectmode, incl_handles, &data);
+  if (any_key_selection_changed) {
+    /* If any key was selected at any time during this process, the entire-curve selection should
+     * be disabled. Otherwise, sliding over any keyless part of the curve will immediately cause
+     * the entire curve to be selected. */
+    RNA_boolean_set(op->ptr, "use_curve_selection", false);
+  }
   const bool use_curve_selection = RNA_boolean_get(op->ptr, "use_curve_selection");
   if (use_curve_selection && !any_key_selection_changed) {
     box_select_graphcurves(&ac, &rect_fl, BEZT_OK_REGION_CIRCLE, selectmode, incl_handles, &data);