Question

I drawn 2 shapes with Bezier curve algorithm with using GL_LINE_STRIP.
My shape likes moon and i want to coloring the space of between two curves.
I used GL_POLYGON but it didn’t produce the result that i want.

This is my Code:

float Points[4][3] = {
{275,356,0},
{ 395,353,0 },
{  435,325,0 },
{ 476,232,0 }
                     };
float SecendPoints[4][3] = {
{ 476,232,0},
{441,331,0},
{369,372,0},
{283,388,0}
                     };
void init()
    {
  glClearColor(0.0,0.0,0.0,0.0);
  glMatrixMode(GL_PROJECTION);
  gluOrtho2D(0.0,640,0.0,480.0);

    }
void Display(void)
    {
  int segment = 20;

   // clear the screen & depth buffer
   glClear(GL_DEPTH_BUFFER_BIT|GL_COLOR_BUFFER_BIT);

   glColor3f(1,1,1);


  glColor3f(1,0,1);

  // we will draw lots of little lines to make our curve

  glBegin(GL_LINE_STRIP);

for(int i=0;i!=segment;++i) {

    // use the parametric time value 0 to 1
    float t = (float)i/(segment-1);

    // nice to pre-calculate 1.0f-t because we will need it frequently
    float it = 1.0f-t;

    // calculate blending functions
    float b0 = t*t*t;
    float b1 = 3*t*t*it;
    float b2 = 3*t*it*it;
    float b3 =  it*it*it;

    // calculate the x,y and z of the curve point by summing
    // the Control vertices weighted by their respective blending
    // functions
    //
    float x = b0*Points[0][0] +
              b1*Points[1][0] +
              b2*Points[2][0] +
              b3*Points[3][0] ;

    float y = b0*Points[0][1] +
              b1*Points[1][1] +
              b2*Points[2][1] +
              b3*Points[3][1] ;

    float z = b0*Points[0][2] +
              b1*Points[1][2] +
              b2*Points[2][2] +
              b3*Points[3][2] ;

    // specify the point
    glVertex3f( x,y,z );
}


for(int i=0;i!=segment;++i) {

    // use the parametric time value 0 to 1
    float t = (float)i/(segment-1);

    // nice to pre-calculate 1.0f-t because we will need it frequently
    float it = 1.0f-t;

    // calculate blending functions
    float b0 = t*t*t;
    float b1 = 3*t*t*it;
    float b2 = 3*t*it*it;
    float b3 =  it*it*it;

    // calculate the x,y and z of the curve point by summing
    // the Control vertices weighted by their respective blending
    // functions
    //
    float x = b0*SecendPoints[0][0] +
              b1*SecendPoints[1][0] +
              b2*SecendPoints[2][0] +
              b3*SecendPoints[3][0] ;

    float y = b0*SecendPoints[0][1] +
              b1*SecendPoints[1][1] +
              b2*SecendPoints[2][1] +
              b3*SecendPoints[3][1] ;

    float z = b0*SecendPoints[0][2] +
              b1*SecendPoints[1][2] +
              b2*SecendPoints[2][2] +
              b3*SecendPoints[3][2] ;

    // specify the point
    glVertex3f( x,y,z );
}
glVertex3f( 476,232,0 );
glEnd();
glFlush();
}

Any Idea?

Answer 1

GL_POLYGON only works correctly for convex polygons.

Tessellate the area between your curves into triangles and render those.