[gtk+] pixelcache: use factor instead of margin

[Christian Hergert <chergert src gnome org>]

commit e55a8b6aefe1ef71d90c06297efb7c40f449e1bc
Author: Christian Hergert <christian hergert me>
Date:   Sun Sep 13 21:08:57 2015 -0700

    pixelcache: use factor instead of margin
    
    Instead of using a fixed size, use a factor of the surface size. This
    helps in situations where animations of surrounding widgets are used
    and cause a rapid rate of surface destroy/create cycles.

 gtk/gtkpixelcache.c |   12 ++++++------
 1 files changed, 6 insertions(+), 6 deletions(-)
---
diff --git a/gtk/gtkpixelcache.c b/gtk/gtkpixelcache.c
index 6661f3d..dae4044 100644
--- a/gtk/gtkpixelcache.c
+++ b/gtk/gtkpixelcache.c
@@ -29,8 +29,8 @@
 
 /* When resizing viewport we allow this extra
    size to avoid constantly reallocating when resizing */
-#define ALLOW_SMALLER_SIZE 32
-#define ALLOW_LARGER_SIZE 32
+#define ALLOW_SMALLER_SIZE_FACTOR 0.5
+#define ALLOW_LARGER_SIZE_FACTOR  1.25
 
 struct _GtkPixelCache {
   cairo_surface_t *surface;
@@ -213,10 +213,10 @@ _gtk_pixel_cache_create_surface_if_needed (GtkPixelCache         *cache,
   /* If current surface can't fit view_rect or is too large, kill it */
   if (cache->surface != NULL &&
       (cairo_surface_get_content (cache->surface) != content ||
-       cache->surface_w < MAX(view_rect->width, surface_w - ALLOW_SMALLER_SIZE) ||
-       cache->surface_w > surface_w + ALLOW_LARGER_SIZE ||
-       cache->surface_h < MAX(view_rect->height, surface_h - ALLOW_SMALLER_SIZE) ||
-       cache->surface_h > surface_h + ALLOW_LARGER_SIZE ||
+       cache->surface_w < MAX(view_rect->width, surface_w * ALLOW_SMALLER_SIZE_FACTOR) ||
+       cache->surface_w > surface_w * ALLOW_LARGER_SIZE_FACTOR ||
+       cache->surface_h < MAX(view_rect->height, surface_h * ALLOW_SMALLER_SIZE_FACTOR) ||
+       cache->surface_h > surface_h * ALLOW_LARGER_SIZE_FACTOR ||
        cache->surface_scale != gdk_window_get_scale_factor (window)))
     {
       cairo_surface_destroy (cache->surface);