#include void gen_tornado( int xs, int ys, int zs, int time, float *tornado ) /* * Gen_Tornado creates a vector field of dimension [xs,ys,zs,3] from * a proceedural function. By passing in different time arguements, * a slightly different and rotating field is created. * * The magnitude of the vector field is highest at some funnel shape * and values range from 0.0 to around 0.4 (I think). * * I just wrote these comments, 8 years after I wrote the function. * * Developed by Roger A. Crawfis, The Ohio State University * */ { float x, y, z; int ix, iy, iz; float r, xc, yc, scale, temp, z0; float r2 = 8; float SMALL = 0.00000000001; float xdelta = 1.0 / (xs-1.0); float ydelta = 1.0 / (ys-1.0); float zdelta = 1.0 / (zs-1.0); for( iz = 0; iz < zs; iz++ ) { z = iz * zdelta; // map z to 0->1 xc = 0.5 + 0.1*sin(0.04*time+10.0*z); // For each z-slice, determine the spiral circle. yc = 0.5 + 0.1*cos(0.03*time+3.0*z); // (xc,yc) determine the center of the circle. r = 0.1 + 0.4 * z*z + 0.1 * z * sin(8.0*z); // The radius also changes at each z-slice. r2 = 0.2 + 0.1*z; // r is the center radius, r2 is for damping for( iy = 0; iy < ys; iy++ ) { y = iy * ydelta; for( ix = 0; ix < xs; ix++ ) { x = ix * xdelta; temp = sqrt( (y-yc)*(y-yc) + (x-xc)*(x-xc) ); scale = fabs( r - temp ); /* * I do not like this next line. It produces a discontinuity * in the magnitude. Fix it later. * */ if ( scale > r2 ) scale = 0.8 - scale; else scale = 1.0; z0 = 0.1 * (0.1 - temp*z ); if ( z0 < 0.0 ) z0 = 0.0; temp = sqrt( temp*temp + z0*z0 ); scale = (r + r2 - temp) * scale / (temp + SMALL); scale = scale / (1+z); *tornado++ = scale * (y-yc) + 0.1*(x-xc); *tornado++ = scale * -(x-xc) + 0.1*(y-yc); *tornado++ = scale * z0; } } } }