OpenGL GL_POLYGON 仅在顺时针绘制时有效？

Question

我是 OpenGL 新手，我尝试使用以下代码 (GL_POLYGON) 使用 python 绘制一个圆。但似乎它只是在以顺时针方式添加点时才绘制它，否则它什么也不绘制

这样就成功画了一个圆

p = self.pos + Y_VEC * self.height  # center of the circle
dv = self.dir_vec * self.radius  # vector point forward
rv = self.right_vec * self.radius  # vector point to right
sides = 20  # sides of the circle (circle is in fact polygon)
angle = 0
        inc = 2 * math.pi / sides
        glColor3f(0, 1, 0)
        glPointSize(10.0)
        glBegin(GL_POLYGON)  # GL_POLYGON drawn but not shown in top view? GL_LINE_LOOP works
        # glVertex3f(*p)  # used for TRIANGLE_FAN
        for i in range(sides+1):
            pc = p + dv * math.cos(angle) + rv * math.sin(angle)
            glVertex3f(*pc)
            angle -= inc
        glEnd()

没有渲染（唯一的变化是“-=”到“+=”）

angle = 0
        inc = 2 * math.pi / sides
        glColor3f(0, 1, 0)
        glPointSize(10.0)
        glBegin(GL_POLYGON)  # GL_POLYGON drawn but not shown in top view? GL_LINE_LOOP works
        # glVertex3f(*p)  # used for TRIANGLE_FAN
        for i in range(sides+1):
            pc = p + dv * math.cos(angle) + rv * math.sin(angle)
            glVertex3f(*pc)
            angle += inc  # change here
        glEnd()

这正常吗？我做错了什么？

Answer 1

确保face culling 被glDisable(GL_CULL_FACE) 禁用。