（OpenGL的）绘制直线，但形状不

Question

我目前正在学习OpenGL和从我的理解，我有画线之前调用

glMatrixMode(GL_PROJECTION); 
glLoadIdentity(); 

。然后，要绘制形状，我需要调用

glMatrixMode(GL_MODELVIEW); 
glLoadIdentity(); 

绘制形状，如GL_TRIANGLES和GL_QUADS。 我写了这段代码，其目的是在顶部绘制一条线和3个形状，但只绘制了一条线。 这是我的代码。

void drawScene() { 
//Clear information from last draw 
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 

glMatrixMode(GL_PROJECTION); //Switch to the drawing perspective 
glLoadIdentity(); //Reset the drawing perspective 



glBegin(GL_LINES); 

glColor3f(100,200,100); 
glLineWidth(10.0f); 
glVertex2f(-1.0f,0.8f); 
glVertex2f(1.0f,0.8f); 

glEnd(); 

glMatrixMode(GL_MODELVIEW); 
glLoadIdentity(); 

glBegin(GL_QUADS); //Begin quadrilateral coordinates 

//Trapezoid 
glVertex3f(-0.7f, -1.5f, -5.0f); 
glVertex3f(0.7f, -1.5f, -5.0f); 
glVertex3f(0.4f, -0.5f, -5.0f); 
glVertex3f(-0.4f, -0.5f, -5.0f); 

glEnd(); //End quadrilateral coordinates 


glBegin(GL_TRIANGLES); //Begin triangle coordinates 

//Pentagon 
glVertex3f(0.5f, 0.5f, -5.0f); 
glVertex3f(1.5f, 0.5f, -5.0f); 
glVertex3f(0.5f, 1.0f, -5.0f); 

glVertex3f(0.5f, 1.0f, -5.0f); 
glVertex3f(1.5f, 0.5f, -5.0f); 
glVertex3f(1.5f, 1.0f, -5.0f); 

glVertex3f(0.5f, 1.0f, -5.0f); 
glVertex3f(1.5f, 1.0f, -5.0f); 
glVertex3f(1.0f, 1.5f, -5.0f); 

//Triangle 
glVertex3f(-0.5f, 0.5f, -5.0f); 
glVertex3f(-1.0f, 1.5f, -5.0f); 
glVertex3f(-1.5f, 0.5f, -5.0f); 

glEnd(); //End triangle coordinates 

glutSwapBuffers(); //Send the 3D scene to the screen 
} 

可能有人请向我解释如何GL_PROJECTION和GL_MODELVIEW以及它们如何工作之间切换？

Answer 1

您的多边形的Z值为-5.0，它在设备坐标的默认[-1,1]范围之外，因此它们会被丢弃。

将所有glVertex3f(x, y, z)调用替换为glVertex2f(x,y)。