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an alpha Q

Started by AndyIC3 Feb 24, 2005 at 5:50 PM 2 replies 800+ views

Original Post

Feb 24, 2005 at 5:50 PM

I know you're supposed to render all your opaque triangles, then do your blended triangles back to front. i'm working on a height map based demo/minigame that has a height map, then "water" that is just a single giant quad with an alpha blended texture. Because this quad is so large, and is the size of the whole map, when should i draw it, before or after? i'm having a hard time getting it to blend for some reason. have been reading tutorials and books and experimenting with no success. how do i post source code on here? maybe someone can take a look

JohnBolton

Feb 24, 2005 at 8:11 PM

You are doing it the right way. Draw all the opaque geometry (the terrain), and then draw all the alpha-blended triangles (the single water quad) back to front. The size of the quad is not important.

AndyIC3

Feb 24, 2005 at 8:16 PM

Well, here's a strange thing... when i draw the water before the terrain, i can see it, but when i render it after the terrain, it doesnt show at all. any ideas?

also, what should i be using for my blend func? here's what i'm using to set up blending:

glBlendFunc( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA );
glEnable( GL_BLEND );

[edit] although it shows when i draw it before the terrain, it is not blended (or it is blended with the clear color.. i can't relaly tell [/edit]

AndyIC3

Feb 24, 2005 at 9:16 PM

i got it!

here's what i did (basically)

init RC with blending off

game loop
{
draw map
turn on & set blending settings
draw water
turn off blending
}

before, i was trying to set all the blending settings when i set up the RC. hope this helps someone

-andy

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