Fix T43867: Clicking outside the viewport exits now Grease Pencil "Continous Draw" mode

When working with a pen only, it was previously impossible to exit Grease Pencil
draw mode (when continous drawing was enabled). Now, clicking outside the drawing region
(e.g. in the timeline, properties editor, or the header/properties/toolshelf regions)
where you are drawing will exit this mode.

Some corner cases to be aware of:
* When Region Overlap is enabled, clicking on the overlapping panels still exits
  draw mode (even though you can see behind the buttons)
* In the Nodes Editor, clicking on a node (while in drawmode) will still draw a
  dot/stroke. But, you can still exit drawmode by clicking on any of the panels
  (properties/toolshelf/header) mentioned earlier
* To cope with cases where the operator is launched from the toolshelf, the
  code now sets a new "active region" when the first stroke is performed
  (based on what region is under the cursor at the time of that stroke),
  overwriting the setting that got stored when invoking the operator (i.e. the toolshelf).
  This change doesn't have any real user-visible effects, other than making it possible for
  this fix to actually work without breaking that use case.

1 files changed, 73 insertions, 15 deletions

diff --git a/source/blender/editors/gpencil/gpencil_paint.c b/source/blender/editors/gpencil/gpencil_paint.c
index 778f98d212e..bcce5cc8fab 100644
--- a/source/blender/editors/gpencil/gpencil_paint.c
+++ b/source/blender/editors/gpencil/gpencil_paint.c
@@ -48,6 +48,7 @@
 #include "BKE_context.h"
 #include "BKE_global.h"
 #include "BKE_report.h"
+#include "BKE_screen.h"
 #include "BKE_tracking.h"
 
 #include "DNA_object_types.h"
@@ -1030,6 +1031,7 @@ static bool gp_session_initdata(bContext *C, tGPsdata *p)
 			/* set current area
 			 *	- must verify that region data is 3D-view (and not something else)
 			 */
+			/* CAUTION: If this is the "toolbar", then this will change on the first stroke */
 			p->sa = curarea;
 			p->ar = ar;
 			
@@ -1938,25 +1940,81 @@ static int gpencil_draw_modal(bContext *C, wmOperator *op, const wmEvent *event)
 			}
 		}
 		else if (event->val == KM_PRESS) {
-			/* Switch paintmode (temporarily if need be) based on which button was used
-			 * NOTE: This is to make it more convenient to erase strokes when using drawing sessions
+			bool in_bounds = false;
+			
+			/* Check if we're outside the bounds of the active region
+			 * NOTE: An exception here is that if launched from the toolbar,
+			 *       whatever region we're now in should become the new region
 			 */
-			if (event->type == LEFTMOUSE) {
-				/* restore drawmode to default */
-				p->paintmode = RNA_enum_get(op->ptr, "mode");
+			if ((p->ar) && (p->ar->regiontype == RGN_TYPE_TOOLS)) {
+				/* Change to whatever region is now under the mouse */
+				ARegion *current_region = BKE_area_find_region_xy(p->sa, RGN_TYPE_ANY, event->x, event->y);
+				
+				printf("found alternative region %p (old was %p) - at %d %d (sa: %d %d -> %d %d)\n",
+					current_region, p->ar, event->x, event->y,
+					p->sa->totrct.xmin, p->sa->totrct.ymin, p->sa->totrct.xmax, p->sa->totrct.ymax);
+				
+				if (current_region) {
+					/* Assume that since we found the cursor in here, it is in bounds
+					 * and that this should be the region that we begin drawing in
+					 */
+					p->ar = current_region;
+					in_bounds = true;
+				}
+				else {
+					/* Out of bounds, or invalid in some other way */
+					p->status = GP_STATUS_ERROR;
+					estate = OPERATOR_CANCELLED;
+					
+					if (G.debug & G_DEBUG)
+						printf("%s: Region under cursor is out of bounds, so cannot be drawn on\n", __func__);
+				}
 			}
-			else if (event->type == RIGHTMOUSE) {
-				/* turn on eraser */
-				p->paintmode = GP_PAINTMODE_ERASER;
+			else if (p->ar) {
+				rcti region_rect;
+				
+				/* Perform bounds check using  */
+				ED_region_visible_rect(p->ar, &region_rect);
+				in_bounds = BLI_rcti_isect_pt_v(&region_rect, event->mval);
 			}
-
-			gpencil_draw_toggle_eraser_cursor(C, p, p->paintmode == GP_PAINTMODE_ERASER);
-
-			/* not painting, so start stroke (this should be mouse-button down) */
-			p = gpencil_stroke_begin(C, op);
-			
-			if (p->status == GP_STATUS_ERROR) {
+			else {
+				/* No region */
+				p->status = GP_STATUS_ERROR;
 				estate = OPERATOR_CANCELLED;
+				
+				if (G.debug & G_DEBUG)
+					printf("%s: No active region found in GP Paint session data\n", __func__);
+			}
+			
+			if (in_bounds) {
+				/* Switch paintmode (temporarily if need be) based on which button was used
+				 * NOTE: This is to make it more convenient to erase strokes when using drawing sessions
+				 */
+				if (event->type == LEFTMOUSE) {
+					/* restore drawmode to default */
+					p->paintmode = RNA_enum_get(op->ptr, "mode");
+				}
+				else if (event->type == RIGHTMOUSE) {
+					/* turn on eraser */
+					p->paintmode = GP_PAINTMODE_ERASER;
+				}
+				
+				gpencil_draw_toggle_eraser_cursor(C, p, p->paintmode == GP_PAINTMODE_ERASER);
+				
+				/* not painting, so start stroke (this should be mouse-button down) */
+				p = gpencil_stroke_begin(C, op);
+				
+				if (p->status == GP_STATUS_ERROR) {
+					estate = OPERATOR_CANCELLED;
+				}
+			}
+			else if (p->status != GP_STATUS_ERROR) {
+				/* User clicked outside bounds of window while idling, so exit paintmode 
+				 * NOTE: Don't eter this case if an error occurred while finding the
+				 *       region (as above)
+				 */
+				p->status = GP_STATUS_DONE;
+				estate = OPERATOR_FINISHED;
 			}
 		}
 		else {