+ const beam_t *b = cl.beams + surfacelist[surfacelistindex];
+ vec3_t beamdir, right, up, offset, start, end;
+ float length, t1, t2;
+
+ CL_Beam_CalculatePositions(b, start, end);
+
+ // calculate beam direction (beamdir) vector and beam length
+ // get difference vector
+ VectorSubtract(end, start, beamdir);
+ // find length of difference vector
+ length = sqrt(DotProduct(beamdir, beamdir));
+ // calculate scale to make beamdir a unit vector (normalized)
+ t1 = 1.0f / length;
+ // scale beamdir so it is now normalized
+ VectorScale(beamdir, t1, beamdir);
+
+ // calculate up vector such that it points toward viewer, and rotates around the beamdir
+ // get direction from start of beam to viewer
+ VectorSubtract(r_refdef.view.origin, start, up);
+ // remove the portion of the vector that moves along the beam
+ // (this leaves only a vector pointing directly away from the beam)
+ t1 = -DotProduct(up, beamdir);
+ VectorMA(up, t1, beamdir, up);
+ // generate right vector from forward and up, the result is unnormalized
+ CrossProduct(beamdir, up, right);
+ // now normalize the right vector and up vector
+ VectorNormalize(right);
+ VectorNormalize(up);
+
+ // calculate T coordinate scrolling (start and end texcoord along the beam)
+ t1 = r_refdef.scene.time * -r_lightningbeam_scroll.value;// + beamrepeatscale * DotProduct(start, beamdir);
+ t1 = t1 - (int) t1;
+ t2 = t1 + beamrepeatscale * length;
+
+ // the beam is 3 polygons in this configuration:
+ // * 2
+ // * *
+ // 1******
+ // * *
+ // * 3
+ // they are showing different portions of the beam texture, creating an
+ // illusion of a beam that appears to curl around in 3D space
+ // (and realize that the whole polygon assembly orients itself to face
+ // the viewer)
+
+ // polygon 1, verts 0-3
+ VectorScale(right, r_lightningbeam_thickness.value, offset);
+ R_CalcLightningBeamPolygonVertex3f(vertex3f + 0, start, end, offset);
+ // polygon 2, verts 4-7
+ VectorAdd(right, up, offset);
+ VectorScale(offset, r_lightningbeam_thickness.value * 0.70710681f, offset);
+ R_CalcLightningBeamPolygonVertex3f(vertex3f + 12, start, end, offset);
+ // polygon 3, verts 8-11
+ VectorSubtract(right, up, offset);
+ VectorScale(offset, r_lightningbeam_thickness.value * 0.70710681f, offset);
+ R_CalcLightningBeamPolygonVertex3f(vertex3f + 24, start, end, offset);
+ R_CalcLightningBeamPolygonTexCoord2f(texcoord2f + 0, t1, t2);
+ R_CalcLightningBeamPolygonTexCoord2f(texcoord2f + 8, t1 + 0.33, t2 + 0.33);
+ R_CalcLightningBeamPolygonTexCoord2f(texcoord2f + 16, t1 + 0.66, t2 + 0.66);
+
+ // draw the 3 polygons as one batch of 6 triangles using the 12 vertices
+ R_DrawCustomSurface(r_lightningbeam_qmbtexture.integer ? r_lightningbeamqmbtexture : r_lightningbeamtexture, &identitymatrix, MATERIALFLAG_ADD | MATERIALFLAG_BLENDED | MATERIALFLAG_FULLBRIGHT | MATERIALFLAG_NOCULLFACE, 0, 12, 0, 6, false, false);