opengl - How to implement adaptive subdivision algorithm for curve in C -


my homework write c program opengl/glut which, after getting groups of 4 points mouse click (points 3 coordinates), should draw bezier curve adaptive algorithm. @ theoretical level it's clear how algorithm works don't know how put in c code. mean @ lesson saw 4 control points have shape similar "trapeze" , algorithm calculates 2 "heights" , checks if satisfy tollerance. problem user might click everywhere in screen , points might not have trapeze-like shape...so, can start from? have

enter image description here

this cole have written, called each time control point added:

if (beziermode == casteljau_adaptive) {     glcolor3f (0.0f, 0.8f, 0.4f); /* draw adaptive casteljau curve in green */     for(i=0; i+3<numcv; += 3)         adaptivedecasteljau3(cv, i, 0.01); }   void adaptivedecasteljau3(float cv[max_cv][3], int position, float tolerance)  {    float x01 = (cv[position][0] + cv[position+1][0]) / 2;   float y01 = (cv[position][1] + cv[position+1][1]) / 2;    float x12 = (cv[position+1][0] + cv[position+2][0]) / 2;   float y12 = (cv[position+1][1] + cv[position+2][1]) / 2;    float x23 = (cv[position+2][0] + cv[position+3][0]) / 2;   float y23 = (cv[position+2][1] + cv[position+3][1]) / 2;    float x012 = (x01 + x12) / 2;   float y012 = (y01 + y12) / 2;    float x123 = (x12 + x23) / 2;   float y123 = (y12 + y23) / 2;    float x0123 = (x012 + x123) / 2;   float y0123 = (y012 + y123) / 2;    float dx = cv[3][0] - cv[0][0];   float dy = cv[3][1] - cv[0][1];    float d2 = fabs(((cv[1][0] - cv[3][0]) * dy - (cv[1][1] - cv[3][1]) * dx));   float d3 = fabs(((cv[2][0] - cv[3][0]) * dy - (cv[2][1] - cv[3][1]) * dx));    if((d2 + d3)*(d2 + d3) < tolerance * (dx*dx + dy*dy)) {        glbegin(gl_line_strip);           glvertex2f(x0123, y0123);       glend();        return;   }    float tmpleft[4][3];   float tmpright[4][3];    tmpleft[0][0] = cv[0][0];   tmpleft[0][1] = cv[0][1];   tmpleft[1][0] = x01;   tmpleft[1][1] = y01;   tmpleft[2][0] = x012;   tmpleft[2][1] = y012;   tmpleft[3][0] = x0123;   tmpleft[3][1] = y0123;    tmpright[0][0] = x0123;   tmpright[0][1] = y0123;   tmpright[1][0] = x123;   tmpright[1][1] = y123;   tmpright[2][0] = x23;   tmpright[2][1] = y23;   tmpright[3][0] = cv[3][0];   tmpright[3][1] = cv[3][1];    adaptivedecasteljau3(tmpleft, 0, tolerance);   adaptivedecasteljau3(tmpright, 0, tolerance);   }

and nothing drawn. have idea?

the begin / end should engulf whole loop, not being inside each isolated vertex !


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