app: only expose the area covered by the vectors object

gimp_display_shell_expose_vectors() exposes the bounding box of
the vectors plus a small border.

app/display/gimpdisplayshell-expose.c

@@ -27,6 +27,8 @@
 #include "core/gimpguide.h"
 #include "core/gimpsamplepoint.h"
 
+#include "vectors/gimpvectors.h"
+
 #include "gimpdisplayshell.h"
 #include "gimpdisplayshell-expose.h"
 #include "gimpdisplayshell-transform.h"
@@ -44,6 +46,26 @@ gimp_display_shell_expose_area (GimpDisplayShell *shell,
   gtk_widget_queue_draw_area (shell->canvas, x, y, w, h);
 }
 
+static void
+gimp_display_shell_expose_region (GimpDisplayShell *shell,
+                                  gdouble           x1,
+                                  gdouble           y1,
+                                  gdouble           x2,
+                                  gdouble           y2,
+                                  gint              border)
+{
+  const gint x = floor (x1);
+  const gint y = floor (y1);
+  const gint w = ceil (x2) - x;
+  const gint h = ceil (y2) - y;
+
+  gimp_display_shell_expose_area (shell,
+                                  x - border,
+                                  y - border,
+                                  w + 2 * border,
+                                  h + 2 * border);
+}
+
 void
 gimp_display_shell_expose_guide (GimpDisplayShell *shell,
                                  GimpGuide        *guide)
@@ -111,11 +133,19 @@ void
 gimp_display_shell_expose_vectors (GimpDisplayShell *shell,
                                    GimpVectors      *vectors)
 {
+  gdouble x1, y1;
+  gdouble x2, y2;
+
   g_return_if_fail (GIMP_IS_DISPLAY_SHELL (shell));
   g_return_if_fail (vectors != NULL);
 
-  // FIXME
+  if (gimp_vectors_bounds (vectors, &x1, &y1, &x2, &y2))
-  gimp_display_shell_expose_full (shell);
+    {
+      gimp_display_shell_transform_xy_f (shell, x1, y1, &x1, &y1, FALSE);
+      gimp_display_shell_transform_xy_f (shell, x2, y2, &x2, &y2, FALSE);
+
+      gimp_display_shell_expose_region (shell, x1, y1, x2, y2, 2);
+    }
 }
 
 void