disable depth write?

(1) The transpareny looks okay to me, but if you want to fix it, allright. BTW: It looks like only the leaves are somewhat transparent. Not the trunk itself. Anyway, to fix it, you need to disable mipmapping. You can scale down the image yourself without blending the Alpha value, but OpenGL will still interpolate around the edges of the leaves if you render the texture. That's what you get even with regular GL_LINEAR textures (PS: Have you tried another texture setting? There is one that doesn't interpolate the pixels at all. Pretty ugly on normal textures, but this could work for you because you use a custom mipmap routine with custom blending. I don't know what the setting is called though. Look it up).

You could also change the depth values at which you switch mipmap textures. Keep the high-res textures for longer.

There is one other way aound it but thats ugly: Alpha testing. It works, but you'll get borders. Maybe you could combine them though:

glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glAlphaTest(GL_GREATER, 0.9f);

Don't know if that would work. It could blend the ugly alphatest borders.

for (2):
It looks like you use additive blending: GL_SRC_APLHA, GL_ONE. Try to use the blendfunc from (1) with GL_ONE_MINUS_SRC_ALPHA.


Sander Maréchal
[Lone Wolves Game Development][RoboBlast][Articles][GD Emporium][Webdesign][E-mail]

[edited by - sander on October 7, 2003 6:13:33 AM]

I just stumbled upon this. You might find it usefull. Especially the second half of the page: how to deal with alpha values in tree billboards.

Sander Maréchal
[Lone Wolves Game Development][RoboBlast][Articles][GD Emporium][Webdesign][E-mail]

Problem 1:
you will have to check the texture that you are rendering to, and find out whether the alpha values in that texture are wrong or not. This could be several problems:
* when rendering to the texture, you may have a residual glColor4f(x,y,z, interpolatealpha) still lying around. Before rendering to the texture try glColor4f(1,1,1,1) first.
* when rendering the imposter you could be doing the same thing
Try a glColor4f(1,1,1,1) first.
* or it may be mipmapping. Not sure, I don''t have much experience with this.

Problem 2:
Are you sure your tree''s bounding box is the correct size?
That 0.424475f looks too much like a scaling factor to me, which may account for the ''squashing effect'' in the pictures. I might be wrong though.

Problem 3:
For rendering any transparent objects (especially if you''re interpolating alpha), you HAVE to depth sort the objects. .
If you draw a mildy opaque object first and then draw a semi-translucent object, it won''t be drawn because the first object was written into the depth-buffer and thus occludes the second object (the phenomenon you see there). If you merely arbitrarily draw the tree model then the billboard it may render fine from one angle, but not from another angle.
Rather, calculate the depth of each translucent object (from the camera) and draw all of them in back to front order. This will eliminate the problem you see in picture 2.

Frey is correct about (3). Ignore my advice on additive blending....

Sander Maréchal
[Lone Wolves Game Development][RoboBlast][Articles][GD Emporium][Webdesign][E-mail]

Good luck! Keep us posted. I''m pretty curious. My team is looking into SpeedTreeRT but that''s sooooo expensive ($6000,-) so we may need to do our own LOD trees after all.

Sander Maréchal
[Lone Wolves Game Development][RoboBlast][Articles][GD Emporium][Webdesign][E-mail]