（OpenGL的）繪製直線，但形狀不

Question

我目前正在學習OpenGL和從我的理解，我有畫線之前調用

glMatrixMode(GL_PROJECTION); 
glLoadIdentity(); 

。然後，要繪製形狀，我需要調用

glMatrixMode(GL_MODELVIEW); 
glLoadIdentity(); 

繪製形狀，如GL_TRIANGLES和GL_QUADS。 我寫了這段代碼，其目的是在頂部繪製一條線和3個形狀，但只繪製了一條線。 這是我的代碼。

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 
} 

可能有人請向我解釋如何GL_PROJECTION和GL_MODELVIEW以及它們如何工作之間切換？

Answer 1

您的多邊形的Z值爲-5.0，它在設備座標的默認[-1,1]範圍之外，因此它們會被丟棄。

將所有glVertex3f(x, y, z)調用替換爲glVertex2f(x,y)。