Not sure if its a bug or my misunderstanding. Here's my understanding of how alpha mode works in GLB
1) if the alphamode = 0 then it draws the sprite normally (no alpha blending at all and the sprite is 100% visible)
2) if the alphamode > 0 then the sprite is drawn with an additive blend i.e. it will be brighter than normal
3) if the alphamode < 0 then the sprite will be transparent i.e. -0.5 alpha mode means the sprite will be 50% transparent and -1.0 means 100% transparency (so its not visible)
Can some one confirm if this is correct?
OK, so if the above is correct then, an alpha mode of 0.5 means the sprite should be brighter. However it is actually 50% transparent when used within a polyvector command. Gernot is there something different we should consider when using alphamode and polyvectors?
After a quick test the range seems to be when using polyvectors...
1 = sprite at 0% transparency (visible)
0.001 = 100% transparency i.e. invisible sprite.
then back to 0% transparency when the alpha mode = 0.
This means to fade out a sprite I need to change the alphamode from 1 to 0.001 which is different from the manual says.