Changes the opacity (also known as alpha, 0.0 transparent - 1.0 opaque) of an image
This can either be used to make an image (semi-)transparent / fully opaque or to temporarily hide an image completely (alpha
Images with a very low alpha value (below 0.0001) are not rendered anymore. This allows you to hide images efficiently by setting their alpha value to 0. Note however that there is still a tiny (but negligible) performance impact even if the image is not rendered. If you are sure that you will not need an image anymore you should remove it with freeimage
If you just want to hide an image it is most efficient to set alpha
to 0. Later set it to a higher value to show it again. Deleting the image with freeimage
and creating a new one causes much more network traffic than hiding it.
Sample 1: Creating an image and changing its opacity