cogl-texture-2d-sliced: Use the smallest possible waste

When picking a size for the last slice in a texture, Cogl would always
pick the biggest power of two size that doesn't create too much
waste and is less than or equal to the previous slice size. However
this can end up creating a texture that is bigger than needed if there
is a smaller power of two.

For example, if the maximum waste is 127 (the current default) and we
try to create a texture that is 257 pixels wide it will decide that
the next power of two (512) is too much waste (255) so it will create
the first slice at 256 pixels wide. Then we only have 1 pixel left to
allocate but Cogl would pick the next smaller size that has a small
enough waste which is 128. But of course 1 is already a power of two
so that's redundantly oversized by 127.

This patch fixes it so that whenever it finds a size that would be big
enough, instead of using exactly that it picks the next power of two
up from the size we need to fill.

http://bugzilla.clutter-project.org/show_bug.cgi?id=2355

(cherry picked from commit 7e112472b5ad9deea9b0ad1fda47aa16199a780a)

1 files changed, 4 insertions, 0 deletions

diff --git a/clutter/cogl/cogl/cogl-texture-2d-sliced.c b/clutter/cogl/cogl/cogl-texture-2d-sliced.c
index 51323df8a..f6fd3bf1a 100644
--- a/clutter/cogl/cogl/cogl-texture-2d-sliced.c
+++ b/clutter/cogl/cogl/cogl-texture-2d-sliced.c
@@ -698,6 +698,10 @@ _cogl_pot_slices_for_size (int    size_to_fill,
       else if (span.size - size_to_fill <= max_waste)
         {
           /* Yes and waste is small enough */
+          /* Pick the next power of two up from size_to_fill. This can
+             sometimes be less than the span.size that would be chosen
+             otherwise */
+          span.size = _cogl_util_next_p2 (size_to_fill);
           span.waste = span.size - size_to_fill;
           if (out_spans)
             g_array_append_val (out_spans, span);