[Jprogramming] alpha in gl2

[Oleg Kobchenko]

> From: June Kim <juneaftn at gmail.com>

> 
> Is there anyway to set the alpha value(transparency) with gl2?

I don't think transparency is supported by gl2 directly,
but it should be easy to achieve though bitblt (glqpixels, glpixels).

See "Image Operations" in J Wiki

   http://www.jsoftware.com/jwiki/OlegKobchenko/Image%20Operations

Basically, for a color component, transparency is weighted sum,
the complement of which to 1 is opacity.

   C = F*O + B*(1 - O)

C is the new color component value
B is the background value (0..1)
F is the foreground value (0..1)
O is the foreground opacity (0..1)