[gimp] app: align display paint area to a coarse grid

[N/A <ell src gnome org>]

commit db50c72c24fffd07d3bdcadc6a633b864d065fac
Author: Ell <ell_se yahoo com>
Date:   Sun Apr 8 09:16:53 2018 -0400

    app: align display paint area to a coarse grid
    
    Align rectangles added to the display paint area, in
    gimp_display_paint_area(), to a coarse grid, to reduce the
    complexity of ther overall area.  This is similar to commit
    49285463e6c0cc03c361902df4e3006fa135dde3, however the alignment
    happens in display space, instead of image space.

 app/display/gimpdisplay.c |   13 ++++++++++++-
 1 files changed, 12 insertions(+), 1 deletions(-)
---
diff --git a/app/display/gimpdisplay.c b/app/display/gimpdisplay.c
index 0ed57de..5966b66 100644
--- a/app/display/gimpdisplay.c
+++ b/app/display/gimpdisplay.c
@@ -50,7 +50,10 @@
 #include "gimp-intl.h"
 
 
-#define FLUSH_NOW_INTERVAL 20000 /* 20 ms in microseconds */
+#define FLUSH_NOW_INTERVAL      20000 /* 20 ms in microseconds */
+
+#define PAINT_AREA_CHUNK_WIDTH  32
+#define PAINT_AREA_CHUNK_HEIGHT 32
 
 
 enum
@@ -902,5 +905,13 @@ gimp_display_paint_area (GimpDisplay *display,
   x2 = ceil (x2_f + 0.5);
   y2 = ceil (y2_f + 0.5);
 
+  /*  align transformed area to a coarse grid, to simplify the
+   *  invalidated area
+   */
+  x1 = floor ((gdouble) x1 / PAINT_AREA_CHUNK_WIDTH)  * PAINT_AREA_CHUNK_WIDTH;
+  y1 = floor ((gdouble) y1 / PAINT_AREA_CHUNK_HEIGHT) * PAINT_AREA_CHUNK_HEIGHT;
+  x2 = ceil  ((gdouble) x2 / PAINT_AREA_CHUNK_WIDTH)  * PAINT_AREA_CHUNK_WIDTH;
+  y2 = ceil  ((gdouble) y2 / PAINT_AREA_CHUNK_HEIGHT) * PAINT_AREA_CHUNK_HEIGHT;
+
   gimp_display_shell_expose_area (shell, x1, y1, x2 - x1, y2 - y1);
 }