[gimp] app: in GimpPaintTool, sync brush-outline coords while painting

[Ell <ell src gnome org>]

commit 5c17d2a43b18a73ffe0af751d616390a0f00e45e
Author: Ell <ell_se yahoo com>
Date:   Fri Jun 8 03:14:17 2018 -0400

    app: in GimpPaintTool, sync brush-outline coords while painting
    
    Add GimpPaintTool::paint_[xy] members, and periodically assign the
    paint core's current coords to them in
    gimp_paint_tool_paint_timeout(), while the main thread and the
    paint thread are synchronized, during painting.
    
    In gimp_paint_tool_draw(), fetch the current coords for the brush
    outline from the above members during painting, instead of directly
    from the paint core, to avoid a race condition with the paint
    thread, so that we always use the correct coordinates at the time
    the paint buffer was flushed back to the drawable.

 app/tools/gimppainttool-paint.c | 11 +++++--
 app/tools/gimppainttool.c       | 65 +++++++++++++++++++++++------------------
 app/tools/gimppainttool.h       |  3 ++
 3 files changed, 49 insertions(+), 30 deletions(-)
---
diff --git a/app/tools/gimppainttool-paint.c b/app/tools/gimppainttool-paint.c
index 96754ff710..aec08b86e9 100644
--- a/app/tools/gimppainttool-paint.c
+++ b/app/tools/gimppainttool-paint.c
@@ -158,13 +158,17 @@ gimp_paint_tool_paint_thread (gpointer data)
 static gboolean
 gimp_paint_tool_paint_timeout (GimpPaintTool *paint_tool)
 {
-  GimpDrawable *drawable = paint_tool->drawable;
-  gboolean      update;
+  GimpPaintCore *core     = paint_tool->core;
+  GimpDrawable  *drawable = paint_tool->drawable;
+  gboolean       update;
 
   paint_timeout_pending = TRUE;
 
   g_mutex_lock (&paint_mutex);
 
+  paint_tool->paint_x = core->cur_coords.x;
+  paint_tool->paint_y = core->cur_coords.y;
+
   update = gimp_drawable_flush_paint (drawable);
 
   if (update && GIMP_PAINT_TOOL_GET_CLASS (paint_tool)->paint_flush)
@@ -248,6 +252,9 @@ gimp_paint_tool_paint_start (GimpPaintTool     *paint_tool,
   curr_coords.x -= off_x;
   curr_coords.y -= off_y;
 
+  paint_tool->paint_x = curr_coords.x;
+  paint_tool->paint_y = curr_coords.y;
+
   /*  If we use a separate paint thread, enter paint mode before starting the
    *  paint core
    */
diff --git a/app/tools/gimppainttool.c b/app/tools/gimppainttool.c
index 757d113b9a..40a2541e68 100644
--- a/app/tools/gimppainttool.c
+++ b/app/tools/gimppainttool.c
@@ -643,46 +643,55 @@ gimp_paint_tool_draw (GimpDrawTool *draw_tool)
       GimpDrawable   *drawable   = gimp_image_get_active_drawable (image);
       GimpCanvasItem *outline    = NULL;
       gboolean        line_drawn = FALSE;
-      gdouble         last_x, last_y;
       gdouble         cur_x, cur_y;
       gint            off_x, off_y;
 
       gimp_item_get_offset (GIMP_ITEM (drawable), &off_x, &off_y);
 
-      last_x = core->last_coords.x + off_x;
-      last_y = core->last_coords.y + off_y;
-      cur_x  = core->cur_coords.x + off_x;
-      cur_y  = core->cur_coords.y + off_y;
-
-      if (paint_tool->draw_line &&
-          ! gimp_tool_control_is_active (GIMP_TOOL (draw_tool)->control))
+      if (gimp_paint_tool_paint_is_active (paint_tool))
+        {
+          cur_x = paint_tool->paint_x + off_x;
+          cur_y = paint_tool->paint_y + off_y;
+        }
+      else
         {
-          GimpCanvasGroup *group;
+          cur_x = core->cur_coords.x + off_x;
+          cur_y = core->cur_coords.y + off_y;
 
-          group = gimp_draw_tool_add_stroke_group (draw_tool);
-          gimp_draw_tool_push_group (draw_tool, group);
+          if (paint_tool->draw_line &&
+              ! gimp_tool_control_is_active (GIMP_TOOL (draw_tool)->control))
+            {
+              GimpCanvasGroup *group;
+              gdouble          last_x, last_y;
 
-          gimp_draw_tool_add_handle (draw_tool,
-                                     GIMP_HANDLE_CIRCLE,
-                                     last_x, last_y,
-                                     GIMP_TOOL_HANDLE_SIZE_CIRCLE,
-                                     GIMP_TOOL_HANDLE_SIZE_CIRCLE,
-                                     GIMP_HANDLE_ANCHOR_CENTER);
+              last_x = core->last_coords.x + off_x;
+              last_y = core->last_coords.y + off_y;
 
-          gimp_draw_tool_add_line (draw_tool,
-                                   last_x, last_y,
-                                   cur_x, cur_y);
+              group = gimp_draw_tool_add_stroke_group (draw_tool);
+              gimp_draw_tool_push_group (draw_tool, group);
 
-          gimp_draw_tool_add_handle (draw_tool,
-                                     GIMP_HANDLE_CIRCLE,
-                                     cur_x, cur_y,
-                                     GIMP_TOOL_HANDLE_SIZE_CIRCLE,
-                                     GIMP_TOOL_HANDLE_SIZE_CIRCLE,
-                                     GIMP_HANDLE_ANCHOR_CENTER);
+              gimp_draw_tool_add_handle (draw_tool,
+                                         GIMP_HANDLE_CIRCLE,
+                                         last_x, last_y,
+                                         GIMP_TOOL_HANDLE_SIZE_CIRCLE,
+                                         GIMP_TOOL_HANDLE_SIZE_CIRCLE,
+                                         GIMP_HANDLE_ANCHOR_CENTER);
 
-          gimp_draw_tool_pop_group (draw_tool);
+              gimp_draw_tool_add_line (draw_tool,
+                                       last_x, last_y,
+                                       cur_x, cur_y);
 
-          line_drawn = TRUE;
+              gimp_draw_tool_add_handle (draw_tool,
+                                         GIMP_HANDLE_CIRCLE,
+                                         cur_x, cur_y,
+                                         GIMP_TOOL_HANDLE_SIZE_CIRCLE,
+                                         GIMP_TOOL_HANDLE_SIZE_CIRCLE,
+                                         GIMP_HANDLE_ANCHOR_CENTER);
+
+              gimp_draw_tool_pop_group (draw_tool);
+
+              line_drawn = TRUE;
+            }
         }
 
       gimp_paint_tool_set_draw_fallback (paint_tool, FALSE, 0.0);
diff --git a/app/tools/gimppainttool.h b/app/tools/gimppainttool.h
index d38d504cb9..8b63f8d408 100644
--- a/app/tools/gimppainttool.h
+++ b/app/tools/gimppainttool.h
@@ -59,6 +59,9 @@ struct _GimpPaintTool
 
   GimpDisplay   *display;
   GimpDrawable  *drawable;
+
+  gdouble        paint_x;
+  gdouble        paint_y;
 };
 
 struct _GimpPaintToolClass