Sprite white out
Post: #1
Hi all,
This seems to have been asked before. But I need a method for Opengl iphone 1.1 i.e. works on a 3g.
I simply wish to draw any sprite with a complete white frame. I haven't got the ram to store every possible animated frame in white aswell.
My only current (and rubbish!) solution is to draw the sprite I require white multiple times with glBlendFunc( GL_SRC_ALPHA, GL_ONE );
Yeah, I know!. But it works!!! :-)
I *assume* there's a much better (more efficient) way to simply draw a white frame rather than multiple draws.
Cheers
This seems to have been asked before. But I need a method for Opengl iphone 1.1 i.e. works on a 3g.
I simply wish to draw any sprite with a complete white frame. I haven't got the ram to store every possible animated frame in white aswell.
My only current (and rubbish!) solution is to draw the sprite I require white multiple times with glBlendFunc( GL_SRC_ALPHA, GL_ONE );
Yeah, I know!. But it works!!! :-)
I *assume* there's a much better (more efficient) way to simply draw a white frame rather than multiple draws.
Cheers
Post: #2
use texture combiners to combine the constant color (1, 1, 1, 1) with the alpha from your sprite?
Post: #3
Hi OSC,
I kind of read about this method, but never found any code example or can be certain it's opengl 1.1 viable.....
Cheers
I kind of read about this method, but never found any code example or can be certain it's opengl 1.1 viable.....
Cheers
Post: #4
It works fine with OpenGL 1.1. Texture combiners are generally a giant pain to set up. Though if all you want to do is output a constant color that is probably not so bad. Maybe only like 10 lines of code? I don't really remember.
Normally you would use GL_MODULATE as your texture ENV mode which multiplies the vertex color against the texture color. You could use GL_ADD instead, but this would only work with specifically 100% white. You wouldn't be able to flash it any other color.
This is an OK article on texture combiners. You would only need to read like the first 1/4 of it maybe.
http://iphone-3d-programming.labs.oreilly.com/ch08.html
Normally you would use GL_MODULATE as your texture ENV mode which multiplies the vertex color against the texture color. You could use GL_ADD instead, but this would only work with specifically 100% white. You wouldn't be able to flash it any other color.
This is an OK article on texture combiners. You would only need to read like the first 1/4 of it maybe.
http://iphone-3d-programming.labs.oreilly.com/ch08.html
Scott Lembcke - Howling Moon Software
Author of Chipmunk Physics - A fast and simple rigid body physics library in C.
Post: #5
assuming (SRC_ALPHA, ONE_MINUS_SRC_ALPHA) blending, something like
Code:
// switch to texture combiner mode
glTexEnvi(GL_TEXTURE_2D, GL_TEXTURE_ENV_MODE, GL_COMBINE);
// calculate color by REPLACE-ing with the CONSTANT TEXTURE_ENV_COLOR
glTexEnvi(GL_TEXTURE_2D, GL_TEXTURE_ENV_COLOR, (GLfloat[]){ 1, 1, 1, 1 });
glTexEnvi(GL_TEXTURE_2D, GL_COMBINE_RGB, GL_REPLACE);
glTexEnvi(GL_TEXTURE_2D, GL_SRC0_RGB, GL_CONSTANT);
glTexEnvi(GL_TEXTURE_2D, GL_OPERAND0_RGB, GL_SRC_COLOR);
// calculate alpha by REPLACE-ing with the alpha from the TEXTURE
glTexEnvi(GL_TEXTURE_2D, GL_COMBINE_ALPHA, GL_REPLACE);
glTexEnvi(GL_TEXTURE_2D, GL_SRC0_ALPHA, GL_TEXTURE);
glTexEnvi(GL_TEXTURE_2D, GL_OPERAND0_ALPHA, GL_SRC_ALPHA);
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