UI: Pan 2D Region When Dragging to Boundary

This adds a modal operator called Edge Pan, which is meant to run invisibly
while something inside a region is being dragged. This patch applies this
to dragging panels, but it can be used elsewhere too.

The speed (which is defined relative to how far the mouse is beyond the
boundary) and delay are easily adjustible. and the speed also increases
smoothly from a start value to a max to make it feel more interactive
and less robotic.

Differential Revision: https://developer.blender.org/D7465

1 files changed, 24 insertions, 10 deletions

diff --git a/source/blender/editors/interface/interface_panel.c b/source/blender/editors/interface/interface_panel.c
index 54f60a05cfd..33f600f30a1 100644
--- a/source/blender/editors/interface/interface_panel.c
+++ b/source/blender/editors/interface/interface_panel.c
@@ -107,6 +107,7 @@ typedef struct uiHandlePanelData {
   int startx, starty;
   int startofsx, startofsy;
   int startsizex, startsizey;
+  float start_cur_xmin, start_cur_ymin;
 } uiHandlePanelData;
 
 typedef struct PanelSort {
@@ -1731,21 +1732,22 @@ static void check_panel_overlap(ARegion *region, Panel *panel)
 
 /************************ panel dragging ****************************/
 
+#define DRAG_REGION_PAD (PNL_HEADER * 0.5)
 static void ui_do_drag(const bContext *C, const wmEvent *event, Panel *panel)
 {
   uiHandlePanelData *data = panel->activedata;
   ScrArea *area = CTX_wm_area(C);
   ARegion *region = CTX_wm_region(C);
-  short align = panel_aligned(area, region), dx = 0, dy = 0;
+  short align = panel_aligned(area, region);
 
-  /* first clip for window, no dragging outside */
-  if (!BLI_rcti_isect_pt_v(&region->winrct, &event->x)) {
-    return;
-  }
+  /* Keep the drag position in the region with a small pad to keep the panel visible. */
+  int x = clamp_i(event->x, region->winrct.xmin, region->winrct.xmax + DRAG_REGION_PAD);
+  int y = clamp_i(event->y, region->winrct.ymin, region->winrct.ymax + DRAG_REGION_PAD);
 
-  dx = (event->x - data->startx);
-  dy = (event->y - data->starty);
+  float dx = (float)(x - data->startx);
+  float dy = (float)(y - data->starty);
 
+  /* Adjust for region zoom. */
   dx *= (float)BLI_rctf_size_x(&region->v2d.cur) / (float)BLI_rcti_size_x(&region->winrct);
   dy *= (float)BLI_rctf_size_y(&region->v2d.cur) / (float)BLI_rcti_size_y(&region->winrct);
 
@@ -1763,17 +1765,21 @@ static void ui_do_drag(const bContext *C, const wmEvent *event, Panel *panel)
     /* reset the panel snapping, to allow dragging away from snapped edges */
     panel->snap = PNL_SNAP_NONE;
 
-    panel->ofsx = data->startofsx + dx;
-    panel->ofsy = data->startofsy + dy;
+    /* Add the movement of the view due to edge scrolling while dragging. */
+    dx += ((float)region->v2d.cur.xmin - data->start_cur_xmin);
+    dy += ((float)region->v2d.cur.ymin - data->start_cur_ymin);
+    panel->ofsx = data->startofsx + round_fl_to_int(dx);
+    panel->ofsy = data->startofsy + round_fl_to_int(dy);
     check_panel_overlap(region, panel);
 
     if (align) {
-      uiAlignPanelStep(area, region, 0.2, true);
+      uiAlignPanelStep(area, region, 0.2f, true);
     }
   }
 
   ED_region_tag_redraw(region);
 }
+#undef DRAG_REGION_PAD
 
 /******************* region level panel interaction *****************/
 
@@ -2967,6 +2973,12 @@ static void panel_activate_state(const bContext *C, Panel *panel, uiHandlePanelS
       data->animtimer = WM_event_add_timer(CTX_wm_manager(C), win, TIMER, ANIMATION_INTERVAL);
     }
 
+    /* Initiate edge panning during drags so we can move beyond the initial region view. */
+    if (state == PANEL_STATE_DRAG) {
+      wmOperatorType *ot = WM_operatortype_find("VIEW2D_OT_edge_pan", true);
+      ui_handle_afterfunc_add_operator(ot, WM_OP_INVOKE_DEFAULT, true);
+    }
+
     data->state = state;
     data->startx = win->eventstate->x;
     data->starty = win->eventstate->y;
@@ -2974,6 +2986,8 @@ static void panel_activate_state(const bContext *C, Panel *panel, uiHandlePanelS
     data->startofsy = panel->ofsy;
     data->startsizex = panel->sizex;
     data->startsizey = panel->sizey;
+    data->start_cur_xmin = region->v2d.cur.xmin;
+    data->start_cur_ymin = region->v2d.cur.ymin;
     data->starttime = PIL_check_seconds_timer();
 
     /* Remember drag drop state even when animating to the aligned position after dragging. */