Lenard Lindstrom wrote:
Here is an example:
...
The bottom circle is purple, not light blue. Drawing is a fill
operation.
No, it's not -- when alpha is involved, it's a blending
operation, or at least it should be.
There's no reason you can't blend the source colours
with the destination colours according to the alpha
value of the source, whether the destination has an
alpha or not.
In other words, a destination with no alpha should be
treated as though it had an implicit alpha of 255
everywhere.