5.5 Opengl编程实例－红蓝三角形

#include <GL/glut.h>

typedef GLfloat point2d[2]; // a point data type

void triangle( point2d a, point2d b, point2d c) // display a triangle

{

    glBegin(GL_TRIANGLES);

    glVertex2fv(a);

    glVertex2fv(b);

    glVertex2fv(c);

    glEnd();

}

void display(void)

{

    point2d v[3] = {{-1.0, -0.58}, {1.0, -0.58}, {0.0, 1.15}}; //initial triangle vertices

    glClear(GL_COLOR_BUFFER_BIT); // Clear display window

    glColor3f(0.0,0.0,1.0); // Set fill color to blue

    glLoadIdentity();//应该放在此处，保证每次显示正确

    glViewport(0, 0, 300, 400); // Set left viewport

    triangle(v[0], v[1], v[2]);

    glColor3f(1.0,0.0,0.0); // Set fill color to red

    glViewport(300, 0, 300, 400); // Set right viewport

    glRotatef(90.0, 0.0, 0.0, 1.0); // Rotate about z axis

    triangle(v[0], v[1], v[2]); // Display blue triangle

    glFlush();

}

void init()

{

    glMatrixMode(GL_PROJECTION);

    //glLoadIdentity();//如果放在此处，会导致第一次显示正确，再次刷新时图形旋转

    gluOrtho2D(-2.0, 2.0, -2.0, 2.0);

    glMatrixMode(GL_MODELVIEW);

    glClearColor(1.0, 1.0, 1.0,1.0);

}

void main(int argc, char **argv)

{

    glutInit(&argc, argv);

    glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);

    glutInitWindowSize(600, 400);

    glutCreateWindow("Triangle");

    glutDisplayFunc(display);

    init();

    glutMainLoop();

}