- int first_point = 0;
-// Need to tabulate every vertex in persistent memory because
-// gluTessVertex doesn't copy them.
- for(int i = 0; i < points.total; i++) {
- MaskPoint *point1 = points.values[i];
- MaskPoint *point2 = (i >= points.total - 1) ?
- points.values[0] : points.values[i + 1];
-
- float x, y;
- int segments = 0;
- if( point1->control_x2 == 0 && point1->control_y2 == 0 &&
- point2->control_x1 == 0 && point2->control_y1 == 0 )
- segments = 1;
-
- float x0 = point1->x, y0 = point1->y;
- float x1 = point1->x + point1->control_x2;
- float y1 = point1->y + point1->control_y2;
- float x2 = point2->x + point2->control_x1;
- float y2 = point2->y + point2->control_y1;
- float x3 = point2->x, y3 = point2->y;
-
- // forward differencing bezier curves implementation taken from GPL code at
- // http://cvs.sourceforge.net/viewcvs.py/guliverkli/guliverkli/src/subtitles/Rasterizer.cpp?rev=1.3
-
- float cx3, cx2, cx1, cx0, cy3, cy2, cy1, cy0;
-
- // [-1 +3 -3 +1]
- // [+3 -6 +3 0]
- // [-3 +3 0 0]
- // [+1 0 0 0]
-
- cx3 = - x0 + 3*x1 - 3*x2 + x3;
- cx2 = 3*x0 - 6*x1 + 3*x2;
- cx1 = -3*x0 + 3*x1;
- cx0 = x0;
-
- cy3 = - y0 + 3*y1 - 3*y2 + y3;
- cy2 = 3*y0 - 6*y1 + 3*y2;
- cy1 = -3*y0 + 3*y1;
- cy0 = y0;
-
- // This equation is from Graphics Gems I.
- //
- // The idea is that since we're approximating a cubic curve with lines,
- // any error we incur is due to the curvature of the line, which we can
- // estimate by calculating the maximum acceleration of the curve. For
- // a cubic, the acceleration (second derivative) is a line, meaning that
- // the absolute maximum acceleration must occur at either the beginning
- // (|c2|) or the end (|c2+c3|). Our bounds here are a little more
- // conservative than that, but that's okay.
- if (segments == 0) {
- float maxaccel1 = fabs(2*cy2) + fabs(6*cy3);
- float maxaccel2 = fabs(2*cx2) + fabs(6*cx3);
-
- float maxaccel = maxaccel1 > maxaccel2 ? maxaccel1 : maxaccel2;
- float h = 1.0;
-
- if(maxaccel > 8.0) h = sqrt((8.0) / maxaccel);
- segments = int(1/h);
- }