OpenGL GL_多边形凹面多边形不上色

Question

在OpenGL中尝试使用多边形时遇到问题。我不知道如何解释，但我的所有顶点都与开始的顶点相连。当我试图给物体上色时，问题就出现了。我想画一个简单的物体。

void TOP (float x1, float y1, float x2, float h,float n)
{
  float r = x2-x1;
  if(n==1){glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);} // FOR FILL OR NO FILL OBJECT
  glBegin(GL_POLYGON);
     glVertex2f(x1,y1);
     glVertex2f(x2,y1);
     glVertex2f(x2,y1+h/7);
     y1=y1+h/7;
     glVertex2f(x2-r/5,y1+h/7);
     x2=x2-r/5; y1=y1+h/7;
     glVertex2f(x2,y1+2*h/7);
     y1=y1+2*h/7;
      glVertex2f(x2+r/5,y1+h/7);
      y1=y1+h/7; x2=x2+r/5;
      glVertex2f(x2,y1+2*h/7);
cout<<y1<<endl;
      y1=y1+2*h/7;
       glVertex2f(x2-r/5,y1); x2=x2-r/5;
      glVertex2f(x2,y1-h/7); y1=y1-h/7;
      glVertex2f(x2-r/5,y1);x2=x2-r/5;
      glVertex2f(x2,y1+h/7); y1=y1+h/7;
      glVertex2f(x2-r/5,y1);x2=x2-r/5;

       glVertex2f(x2,y1-h/7); y1=y1-h/7;
       glVertex2f(x2-r/5,y1);x2=x2-r/5;
        glVertex2f(x2,y1+h/7); y1=y1+h/7;
         glVertex2f(x2-r/5,y1);x2=x2-r/5;
         glVertex2f(x2,y1-2*h/7);y1=y1-2*h/7;
         glVertex2f(x2+r/5,y1-h/7);y1=y1-h/7; x2=x2+r/5;
         glVertex2f(x2,y1-2*h/7); y1=y1-2*h/7;
         glVertex2f(x2-r/5,y1-h/7); y1=y1-h/7;x2=x2-r/5;
          glVertex2f(x2,y1-h/7);

  glEnd();
}

输出：

Answer 1

GL_POLYGON仅用于convex polygons。

对于concave polygons至少有两个选项：

1. Triangulate the polygon并使用GL_TRIANGLES。

2. Use the stencil buffer trick。