Why do image lists and tool bars use horizontal strips if vertical is so much better?

Raymond Chen

Two people pointed out that the ImageList_Add function and toolbars use horizontal strips even though we learned that vertical strips are much more efficient. While it’s true that the images are passed to the ImageList_Add and CreateToolbarEx functions in horizontal strips, the image list and toolbar code copy them to a vertical strip.

In other words, the horizontal strip is merely an interchange format. Internally, the image list and toolbar use the more efficient vertical arrangement.