为什么多个函数调用不工作在Opengl?

Question

我尝试使用不同的函数来制作各种对象，并在我的Opengl项目中通过一个函数(如display())调用。但是它不起作用，当我调用两个函数时然后给我一个函数另一个没有显示，我不知道为什么，

我已经试过了:

#include <windows.h>  // for MS Windows
#include <GL/glut.h>  // GLUT, include glu.h and gl.h
#include <math.h>

void box() {
glClearColor(1.0f, 1.0f, 1.0f, 1.0f); // Set background color to black and opaque
glClear(GL_COLOR_BUFFER_BIT);         // Clear the color buffer (background)
// Draw a Red 1x1 Square centered at origin
glBegin(GL_POLYGON);              // Each set of 4 vertices form a quad
glColor3f(1.0f, 0.0f, 0.0f); // Red
glVertex2f(-0.9f, -0.7f);
glVertex2f(-0.9f, 0.7f);
glVertex2f(0.9f, 0.7f);
glVertex2f(0.9f, -0.7f);    // x, y
glEnd();

glFlush();  // Render now

}
void triangle()
{
glClearColor(1.0f, 1.0f, 1.0f, 1.0f); // Set background color to black and opaque
glClear(GL_COLOR_BUFFER_BIT);
glBegin(GL_POLYGON);              // Each set of 4 vertices form a quad
glColor3f(0.0f, 1.0f, 0.0f); // green
glVertex2f(-0.9f, -0.7f);
glVertex2f(-0.4f, 0.7f);
glVertex2f(0.1f, -0.7f);    // x, y
glEnd();

glFlush();  // Render now
}
void display()
{
box();
triangle();
}
/* Main function: GLUT runs as a console application starting at main()  */
int main(int argc, char** argv) {
glutInit(&argc, argv);
glutInitWindowSize(1000, 600);// Set the window's initial width & height
glutCreateWindow("OpenGL Setup Test");
//gluOrtho2D(-0.1,0.7,-0.1,0.3); // Create a window with the given title
//glutInitWindowSize(500, 500);// Set the window's initial width & height
glutDisplayFunc(display);// Register display callback handler for window re-paint
glutMainLoop();           // Enter the event-processing loop
return 0;
}

有什么建议吗

Answer 1

在呈现每个形状之前清除缓冲区，从而擦除刚才绘制的形状。相反，您应该在每个display中只清除一次。glFlush:

void box() {
// Draw a Red 1x1 Square centered at origin
glBegin(GL_POLYGON);
glColor3f(1.0f, 0.0f, 0.0f); // Red
glVertex2f(-0.9f, -0.7f);
glVertex2f(-0.9f, 0.7f);
glVertex2f(0.9f, 0.7f);
glVertex2f(0.9f, -0.7f);    // x, y
glEnd();
}
void triangle()
{
glBegin(GL_POLYGON);
glColor3f(0.0f, 1.0f, 0.0f); // green
glVertex2f(-0.9f, -0.7f);
glVertex2f(-0.4f, 0.7f);
glVertex2f(0.1f, -0.7f);    // x, y
glEnd();
}
void display()
{
glClearColor(1.0f, 1.0f, 1.0f, 1.0f); // Set background color to white and opaque
glClear(GL_COLOR_BUFFER_BIT);         // Clear the color buffer (background)
box();
triangle();
glFlush();  // Render now
}