Quake Standards Group

Tutorial *75*

Right. In this tutorial, I'm just fixing up a minor issue involving the way ID chose to render flashblends, and fovs higher than 90.

First I'll explain the theory, then I'll show you the fix i implemented:

(you can skip this part if you don't care)

The flashblend effect, known to the more technically minded as the orange balls of glowy stuff around explosions and muzzleflashes in glquake, when gl_flashblend is set to 0, is not rendered as a sphere, nor is it a circle. It's basically a cone, made out of a triangle fan, with one point in the middle with a higher alpha, and those around the edge with zero alpha. OpenGL smooths them out to look like a spherical glow. So that they cover the entire model that theyre surrounding, and to give them a bit more depth, the centre point must be moved a little nearer to the view. ID software chose to move the centre point along the line called 'vpn', which is a vector that points in the direction the player is looking - perpendicular to the screen. The result is that flashblends which are further from the centre of the screen look like their centre point is further away from the centre of the screen than the actual centre of the blend's perimeter. This is because the centre point is moved along a line perpendicular to the screen, and not one which points towards the viewpoint. This is all fine and dandy with a fov of 90, which is why i think ID left it at that - it does look quite cool. However, at higher fovs, the centrepoint can appear outside the perimeter, and by strafing you can see how they actually are cones. THIS IS ABSOLUTELY HEADWRECKING if you have a lot of glows in the map, particularly with the model glow effects tutorial, where all the torches in the map get the glow effect.
The fix is quite simple, move the centrepoint towards the viewpoint and not just the screen. If you actually bothered to read this, you could probably do it now, and save yourself the hassle of copying and pasting.

Now here's the actual code:

For gl_flashblend, find r_RenderDlight, in gl_rlight.c, and add this line after all the other variable definitions:



	vec3_t	vp2;//dave - slight fix

then go to this line:



	glBegin (GL_TRIANGLE_FAN);

and immediately above, add this:



	VectorSubtract (light->origin, r_origin, vp2);

	VectorNormalize(vp2);

then change the line:



	for (i=0 ; i<3 ; i++)

		v[i] = light->origin[i] - vpn[i]*rad;

to say:



	for (i=0 ; i<3 ; i++)

		v[i] = light->origin[i] - vp2[i]*rad;

Then compile, fix all the compile errors, compile, and flashblends won't bug you when seen out of the corner of the eye.

Now for model glows. I'm assuming here that you haven't messed around with it any, because if you have, you can probably work out the changes you will need.

Go to gl_rmain.c and find R_DrawAliasModel. Add this to the variable definitions at the top:



	vec3_t		vp2;

Then find this:



		VectorSubtract(lightorigin, r_origin, v);



		// See if view is outside the light.

		distance = Length(v);

		if (distance > radius) {

and replace with:



		VectorSubtract(lightorigin, r_origin, vp2);



		// See if view is outside the light.

		distance = Length(vp2);

		if (distance > radius) {



			VectorNormalize(vp2);

Then find:



			for (i=0 ; i<3 ; i++)

				v[i] = lightorigin[i] - vpn[i]*radius;

and replace with:



			for (i=0 ; i<3 ; i++)

				v[i] = lightorigin[i] - vp2[i]*radius;

Then if nothing goes wrong, the glow effects will not bug you at all, ever.
This peace of mind was brought to you by KrimZon.