[nautilus] canvas-container: fix desktop snapping

[Carlos Soriano Sánchez <csoriano src gnome org>]

commit 984438f1028580d3be65ee1d27f99dd84448c97f
Author: Carlos Soriano <csoriano gnome org>
Date:   Mon Feb 1 09:40:46 2016 +0100

    canvas-container: fix desktop snapping
    
    To snap an icon to the closest grid cell, we were trying to round
    the x position with an offset of 0.5. However, cells are not
    normalized, so that 0.5 is actually doing little to round the
    position.
    
    This is making the icons to snap to the right closest cell once the
    user drags more the icon left to the current cell.
    
    The actual size of the cell is SNAP_SIZE_*, so to fix this use half
    of the SNAP_SIZE to "round" the number.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=750446

 libnautilus-private/nautilus-canvas-container.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/libnautilus-private/nautilus-canvas-container.c b/libnautilus-private/nautilus-canvas-container.c
index 84e6523..e3d0bd7 100644
--- a/libnautilus-private/nautilus-canvas-container.c
+++ b/libnautilus-private/nautilus-canvas-container.c
@@ -109,8 +109,8 @@
 #define SNAP_HORIZONTAL(func,x) ((func ((double)((x) - DESKTOP_PAD_HORIZONTAL) / SNAP_SIZE_X) * SNAP_SIZE_X) 
+ DESKTOP_PAD_HORIZONTAL)
 #define SNAP_VERTICAL(func, y) ((func ((double)((y) - DESKTOP_PAD_VERTICAL) / SNAP_SIZE_Y) * SNAP_SIZE_Y) + 
DESKTOP_PAD_VERTICAL)
 
-#define SNAP_NEAREST_HORIZONTAL(x) SNAP_HORIZONTAL (floor, x + .5)
-#define SNAP_NEAREST_VERTICAL(y) SNAP_VERTICAL (floor, y + .5)
+#define SNAP_NEAREST_HORIZONTAL(x) SNAP_HORIZONTAL (floor, x + SNAP_SIZE_X / 2)
+#define SNAP_NEAREST_VERTICAL(y) SNAP_VERTICAL (floor, y + SNAP_SIZE_Y / 2)
 
 #define SNAP_CEIL_HORIZONTAL(x) SNAP_HORIZONTAL (ceil, x)
 #define SNAP_CEIL_VERTICAL(y) SNAP_VERTICAL (ceil, y)