Long Version:
I know you can use a PNG24 on a quad and float it in 3d but what happens when you spin the camera around the quad? Your nice flare or what have you will be really skinny and at some angles non-existent. Is there a way to implement a sprite object so that you don't have to use code to keep re orientating your quad so that it's face to face with the camera?

Short Version:
Plunk down an image in 3d so that it's always facing the camera. Anyway to do itbesides always rotating a Quad with the image as a texture?

Please no strictly OpenGL suggestions (hacks), I'd like to stay flexible and stick to a processing solution for portability to P3D.

Many thanks! I suppose you could write your own library for a sprite object and then just use that. I was curious if the functionality was already built in.

Thanks!!!

here is a quick way of rotating particles to face the camera.

float deltaX = camTarget.x - camPosition.x;
float deltaY = camTarget.y - camPosition.y;
float deltaZ = camTarget.z - camPosition.z;

float angleZ   = atan2( deltaY,deltaX );
float hyp      = sqrt( sq( deltaX ) + sq( deltaY ) );
float angleY   = atan2( hyp,deltaZ );

gl.glPushMatrix();
gl.glTranslatef( loc.x, loc.y, loc.z );
gl.glRotatef( degrees( angleZ ), 0, 0,    1.0f );
gl.glRotatef( degrees( angleY ), 0, 1.0f, 0    );
gl.glScalef( renderSize, renderSize, 0 );
gl.glBegin( GL.GL_QUADS );

gl.glColor4f( 1, 1, 1, 1 );
gl.glTexCoord2f( 0, 0 );
gl.glVertex3f( -0.5f, -0.5f, 0 );
gl.glTexCoord2f( 0, 1 );
gl.glVertex3f( -0.5f,  0.5f, 0 );
gl.glTexCoord2f( 1, 1 );
gl.glVertex3f(  0.5f,  0.5f, 0 );
gl.glTexCoord2f( 1, 0 );
gl.glVertex3f(  0.5f, -0.5f, 0 );

gl.glEnd();
gl.glPopMatrix();

problem with this method is the particles rotate around the Z axis, not sure why.  Won't notice this is your particle texture is circular but you will notice it rotate if its any other shape.

Yeah... that didn't work at all. I miss understood the relationship of the rotation. Seems that the rotation of the sprite controlled by movement on all three axii. Will be tough to nail that down.

Any other ideas?

Perfect, thanks selter.

EDIT: I apologize. I'm too often eager to jump to answers before i have given the problem my full attention ( let's call it ego creep ). My suggestion below is _strictly_ openGL and consequently an invalid suggestion to the initial question. I will leave it in-tact just for those who are searching the forums...

The fastest way i have found to do billboards in _pure openGL_ is point sprites (if your card works with them). I will be posting a way to do fast 2d text right after i finish this reply using Point sprites. They are _always_ facing the camera. They have absolutely no rotation whatsoever.
Basically a point sprite is a texture across a point so that you only have to specify the center of the sprite instead of 4 for a quad - in other words its pretty efficient but it can be tricky.

Important Note: Point Sprites will only work with Power of Two textures created with GL_TEXTURE_2D. this is because the texture coordinates are automatically generated across a range of 0.0-1.0. Non Power of Two textures use actual pixel distance to specify texture coordinates and so they don't work.

Example Time:

Code:

//enable point sprites
gl.glEnable(GL.GL_POINT_SPRITE);
//set up auto tex coords, point sprites wont work without it
gl.glTexEnvi(GL.GL_POINT_SPRITE, GL.GL_COORD_REPLACE, GL.GL_TRUE);

gl.glBegin(GL.GL_POINTS);
for( int i=0; i< NumberOfSprites; i++){
    gl.glPointSize(Sprite[i].Size);
    //render all your points here
    gl.glVertex3f(  Sprite[i].centerX, Sprite[i].centerY, Sprite[i].Z );
}
gl.glEnd();
 

Now about the sprite size: You can change the sprite size for each individual sprite or let openGL do it for you. If you want to let openGL do it look into the parameters
Code:

glPointParameterfARB( GL_POINT_FADE_THRESHOLD_SIZE_ARB, ### );
glPointParameterfARB( GL_POINT_SIZE_MIN_ARB, ### );
glPointParameterfARB( GL_POINT_SIZE_MAX_ARB, ### );
glPointParameterfvARB( GL_POINT_DISTANCE_ATTENUATION_ARB,  ###);
 

Hello all,
  Hopefully I can reply in this thread and get some eyes!  I am using point sprites after very excitedly finding out about them from this thread and others.  I have run into a bit of a snag.  Looking at ness's example above, it seems that you should be able to change the size of individual sprites within the same gl.glBegin(GL.GL_POINTS) -->  gl.glEnd() sequence.  Unfortunately, I could never get it to work, and ended up calling a new glBegin upon every iteration in my array of points, in order to get them to be different sizes.
  Now, in the hopes of improving real time performance, I'd like to revisit this problem and see if anyone knows what's up.  Firstly, if I could change the point size within the glBegin command, would this improve my performance?  And secondly, if I can do this, what am I doing wrong?
  When I put the gl.glPointSize command within the points iteration, it reduces all of the sprites' size to tiny specks.  Here is the offending code:

Quote:


and here is what I have had to do to make it work (including colorizing the sprites):

Quote:


Any help would be greatly appreciated, thank you!