rotation question

can I suggest you render you particles in a slightly different way?
I realise this might be annoying but it will liky help you solve this problem and also more in the future and also likly be a lot faster...

you currently use pushMatrix..popMatrix for each particle, and I guess, also use glTranslate, glRotate, etc, for each as well.. Honestly, this is quite slow and difficult to debug when things go wrong.

I guess you already have your particle positions stored? then, what you can do is work out where 4 vertices should be to create a front facing particle for the entire particle emitter (or even entire scene) and then go through each particle, draw 4 vertices with each being the particle position plus each of those 4 positions.
There is a nice easy way you can get there values too, through the modelview matrix:

//these are the two vertex offsets that can make a front facing particle (negative makes the other 2 verts) - they should be stored someplace.. computed when settings the camera

float vec1[3], vec2[3];



float mvMat[16];

glGetFloatv(GL_MODELVIEW_MATRIX,mvMat);


vec1[0] =  mat[0] + mat[4];
vec1[1] =  mat[1] + mat[5];
vec1[2] =  mat[2] + mat[6];

vec2[0] = -mat[0] + mat[4];
vec2[1] = -mat[1] + mat[5];
vec2[2] = -mat[2] + mat[6];

ok, then when you render a particle (as quads), it would just be:

 float x= ,y= ,z=; // particle position - I assume they are set...


 glVertex(x + vec1[0] , y + vec1[1] , z + vec1[2]);
 glVertex(x + vec2[0] , y + vec2[1] , z + vec2[2]);
 glVertex(x - vec2[0] , y - vec2[1] , z - vec2[2]);
 glVertex(x - vec1[0] , y - vec1[1] , z - vec1[2]);

vec1 and vec two should be scaled to the size of the particle of course.

The reason it works is because in the modelview matrix mat[0],mat[1] and mat[2] are effectivly a vector pointing ''left'' and mat[4], mat[5], and mat[6], effectivly point ''up''.. so you combine them you get up-left and down-left.. negate them and you then get down-right and up-right.. all relitive to the direction you are looking (hence useful in rendering sprites).

I can''t guarentee that code worked btw, I wrote it as is just then so I can''t say it will work.




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