OpenGL programming easy to get started nurbs curves and surfaces (2)

Example 12: Draw a color curve, the curve closed synthesis circle. Draw 8 points at the edge of the curve, as shown in Figure 14.

#include <windows.h> #include <GL/glut.h> Glunurbsobj *thenurb; Glfloat Ctrlpoints[12][3] = {{4,0,0},{2.828,2.828,0},{0,4,0},{-2.828,2.828,0}, { -4,0,0},{-2.828,-2.828,0},{0,-4,0},{2.828,-2.828,0}, {4,0,0},{2.828,2.828,0},{0,4,0},{2.828,2.828,0}};//Control point Glfloat color[12][3]={{1.0,0.0,0.0},{1.0,1.0,0.0},{0.0,1.0,0.0},{-1.0,1.0,0.0}, { -1.0,0.0,0.0},{-1.0,-1.0,0.0},{0.0,-1.0,0.0},{1.0,-1.0,0.0}, {1.0,0.0,0.0},{1.0,1.0,0.0},{0.0,1.0,0.0},{1.0,1.0,0.0}}; Glfloat knots[15] = {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}; void Myinit (void) { Glclearcolor (1.0,1.0,1.0,0.0);/Set Background color Thenurb = Glunewnurbsrenderer ();//Create a NURBs object thenurb Glunurbsproperty (thenurb,glu_sampling_tolerance,10); } /* Draw Curve * * void Mydisplay (void) { int i; Glclear (Gl_color_buffer_bit|gl_depth_buffer_bit); glcolor3f (0.0,0.0,0.0); Gllinewidth (3.0); /* Draw Curve * * Glubegincurve (THENURB); Glunurbscurve (Thenurb,15,knots,3,&ctrlpoints[0][0],3,gl_map1_vertex_3); Glunurbscurve (thenurb,15,knots,3,&ctrlpoints[0][0],3,gl_map1_color_4); Gluendcurve (THENURB); /* Draw Point * * glcolor3f (1.0,0.0,0.0); Glpointsize (5.0); Glbegin (gl_points); for (i = 0;i < 8;i++) GLVERTEX2FV (&ctrlpoints[i][0]); Glend (); Glutswapbuffers (); } void Myreshape (Glsizei w,glsizei h) { Glviewport (0,0,W,H); Glmatrixmode (gl_projection); Glloadidentity (); if (w <=h) Glortho ( -10.0,10.0,-10.0* (glfloat) h/(glfloat) w,10.0* glfloat (h/) glfloat); Else Glortho ( -10.0* (glfloat) w/(glfloat) h,10.0* glfloat (w/) glfloat); Glmatrixmode (Gl_modelview); Glloadidentity (); Gltranslatef (0.0,0.0,-9.0); } int main (int argc,char * * argv) { /* Initialize * * Glutinit (&AMP;ARGC,ARGV); Glutinitdisplaymode (glut_double| glut_rgb| Glut_depth); Glutinitwindowsize (600,400); Glutinitwindowposition (200,200); /* Create window * * Glutcreatewindow ("NURBS curve"); /* Draw and display * * Myinit (); Glutreshapefunc (Myreshape); Glutdisplayfunc (Mydisplay); Glutmainloop (); return (0); }

Glubegincurve,gluendcurve to qualify nurbs surfaces. The return value is void and the parameters are glunurbsobj* nobj, which is a pointer to a NURBs object.

void Glunurbscurve (Glunurbsobj *nobj, Glint nknots, glfloat *knot, Glint stride, Glfloat *ctlarray, GLint order,glenum ty PE) to define the shape of the curve.

Nobj a pointer to a NURBs object.

Nknots number of nodes, node points equals control points plus order.

Knot nknots Array Non-descending node value.

Stride the offset of adjacent control points.

Ctlarry A pointer to an array of control points for NURBS.

Order NURBs Curve, the order number is 1 larger than the dimension.

Type surface types.

Figure 14: NURBs curve