[Gambas-user] gb3: DrawAlpha

Kevin Fishburne kevinfishburne at ...1887...
Tue Jul 5 04:39:11 CEST 2011

Since DrawImage just copies the RGBA channels and PaintImage blends the 
channels using the alpha channel, I'm assuming that DrawAlpha copies 
(but does not blend) the alpha channel. Is that the case?

If so then it follows there should be a PaintAlpha, which blends one 
alpha channel into another rather than overwriting it. Or maybe there's 
a workaround that I haven't thought of.

What I'm trying to do is this:

1) Create a landscape image
2) Create a solar lighting image
3) Create an object lighting image
4) Composite them

The landscape image is just the landscape with no lighting. The solar 
lighting image is RGBA and reflects the solar light level and color tint 
applied to the landscape image. The object lighting image is pure alpha 
and is generated by whatever non-solar light sources are in the scene 
(fire, generally). It should modify only the solar lighting image 
(blending its alpha channel), which is then drawn on top of the 
landscape image via PaintImage. This will allow the landscape to be 
colored and darkened by the solar lighting image, which has had "holes" 
made in it by the object lighting image.

Is any of this possible? I've been thinking about it for about a week 
and have just started to implement code to experiment. I also have some 
gut feeling that I may need to invert an alpha channel to accomplish 
this, but there's no evidence to support that yet. Any thoughts are 
appreciated as always.

Kevin Fishburne
Eight Virtues
www: http://sales.eightvirtues.com
e-mail: sales at ...1887...
phone: (770) 853-6271

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