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  Bitmask transparency  (Read 1299 times)
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Offline mudman

Junior Devvie

Here we go again...

« Posted 2006-04-11 13:35:52 »

Since hardware acceleration of Java2d supports bitmask transparency shouldn't it be possible to use it in OpenGL too?
I can't seem to find anything indicating this.
(I understand there are 2 kinds of "bitmask" transparency - one is assigning a special color as transparent, the other is using a 1 bit black/white texture as bitmask. The last option would be preferrable)
Offline darkprophet

Senior Devvie

Go Go Gadget Arms

« Reply #1 - Posted 2006-04-12 23:56:59 »

tis called alpha testing Smiley

GL11.glAlphaFunc( GL11.GL_GREATER, 0);

what that basically does is pass fragments through the test that have a transperancy of > 0, upon which it then goes through the stencil test (if enabled), then the depth test (if enabled) before being rasterised.


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Offline mudman

Junior Devvie

Here we go again...

« Reply #2 - Posted 2006-04-13 08:48:19 »

Then I would have to use RGBA images to make it work I think?
 Is there any way I can use a 1 bit black/white image to mask out a 24 bit RGB image, or define one of the colors in a 24 bit image as translucent? I would prefer being able to use masking, since this is for isometric tiles, and 50% of the rectangle containing a tile is transparent - that way I could save 50% space if I just used the same mask texture for all tiles.
I looked at polygon stipples, but they are only 32X32.
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Offline darkprophet

Senior Devvie

Go Go Gadget Arms

« Reply #3 - Posted 2006-04-13 09:12:18 »

I would suggest using RGBA, but define the internal format as RGB5_A1, that gives you 5 bits for each red, green and blue components and 1 bit for alpha resulting in a combined 16 bit image...

If you really really dont want RGBA, then your going to have to use multitexturing with one channel having RGBA8 and one having Alpha4; your still going to have to deal with the overhead of seperate textures and mulitexturing.

Look here for the internal format listing.


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Offline CaptainJester

JGO Knight

Medals: 12
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Make it work; make it better.

« Reply #4 - Posted 2006-04-13 12:02:40 »

You could look at the NeHe tutorial that does just what you are trying to do.  It also includes the source in LWJGL.

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