c++ - 带有GLUT的OpenGL-黑屏

我想收到四个三角形的小动画。我写了几个版本的代码，但是这些版本都不起作用。结果，我黑屏了。
我的代码:

#define GLUT_DISABLE_ATEXIT_HACK
#define TIMERSECS 20

#include <windows.h>
#include <GL/glut.h>
#include <GL/gl.h>
#include <GL/GL.H>
#include <stdlib.h>

float arc = 0.0f;

void draw_traingle(float x0, float y0, float x1, float y1, float x2, float y2) {
    glColor4f(0.0f, 0.0f, 1.0f, 1.0f); //Blue
    glVertex2f(x0, y0);
    glVertex2f(x1, y1);
    glVertex2f(x2, y2);
}

void draw(void) {
    glLoadIdentity();
    glClear(GL_COLOR_BUFFER_BIT);
    glRotatef(arc, 1.0f,0.0f,0.0f);

    glBegin(GL_POLYGON);

    float center_x = 300.0f;
    float center_y = 300.0f;

    float up_x = center_x;
    float up_y = 250.0f;

    float down_x = center_x;
    float down_y = 350.0f;

    float right_x = 350.0f;
    float right_y = center_y;

    float left_x = 250.0f;
    float left_y = center_y;
    glPushMatrix();
    draw_traingle(up_x, up_y, right_x, right_y, center_x, center_y);
    draw_traingle(right_x, right_y, down_x, down_y, center_x, center_y);
    draw_traingle(down_x, down_y, left_x, left_y, center_x, center_y);
    draw_traingle(left_x, left_y, up_x, up_y, center_x, center_y);
    glPopMatrix();
    glEnd();
    glFlush();
    glutSwapBuffers();
}

void handleKeypress(unsigned char key, int x, int y) {
    switch (key) {
    case 27:
        exit(0);
    }
}
void init(void) {
    glClearColor(0.0, 0.0, 0.0, 0.0);
    glViewport(0, 0, 600, 600);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity(); //=1
    gluOrtho2D(0.0, 600.0, 0.0, 600.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity(); //=1
}
void update(int value) {
    arc += 2.0f;
    if (arc > 360.f) {
        arc -= 360;
    }
    glutPostRedisplay();
    glutTimerFunc(TIMERSECS, update, 0);
}
int main(int argc, char** argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); //single buffer and RGBA
    glutInitWindowSize(600, 600);
    glutInitWindowPosition(100, 100);
    glutCreateWindow("Window");
    init();
    glutDisplayFunc(draw);
    glutTimerFunc(TIMERSECS, update, 0);
    glutKeyboardFunc(handleKeypress);
    glutMainLoop();
    return 0;
}

我想创建一个动画，其中从小火车建立的矩形每隔一小段时间旋转2度。我想像时钟一样旋转它。我知道问题不是及时的(不是太小)，而是在glRotatef中-我不知道应该给我适当的效果应该使用什么参数。

提前致谢! :)

最佳答案

#include <GL/glut.h>
#include <GL/gl.h>
#include <stdlib.h>
//#define TIMERSECS 200 prefer not to use preprocessor macros
//instead you can use:
static const int TIMERSECS = 200;

float arc = 0.0f;

void draw_traingle(float x0, float y0, float x1, float y1, float x2,     float y2) {
    glBegin(GL_POLYGON);
    glColor4f(0.0f, 0.0f, 1.0f, 1.0f); //Blue
    glVertex2f(x0, y0);
    glVertex2f(x1, y1);
    glVertex2f(x2, y2);
    glEnd();
}

void draw(void) {
    glClear(GL_COLOR_BUFFER_BIT);
    glTranslatef(300, 300, 0);
    glRotatef(arc, 0.0f,0.0f,1.0f);
    glTranslatef(-300, -300, 0);

    float center_x = 300.0f;
    float center_y = 300.0f;

    float up_x = center_x;
    float up_y = 250.0f;

    float down_x = center_x;
    float down_y = 350.0f;

    float right_x = 350.0f;
    float right_y = center_y;

    float left_x = 250.0f;
    float left_y = center_y;
    draw_traingle(up_x, up_y, right_x, right_y, center_x,     center_y);
    draw_traingle(right_x, right_y, down_x, down_y, center_x, center_y);
    draw_traingle(down_x, down_y, left_x, left_y, center_x, center_y);
    draw_traingle(left_x, left_y, up_x, up_y, center_x, center_y);

    glutSwapBuffers();
}

void handleKeypress(unsigned char key, int x, int y) {
    switch (key) {
    case 27:
            exit(0);
    }
}

void init() {
    glClearColor(0.0, 0.0, 0.0, 0.0);
    glViewport(0, 0, 600, 600);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity(); //=1
    gluOrtho2D(0.0, 600.0, 0.0, 600.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity(); //=1
}
void update(int value) {
    arc += 2.0f;
    if (arc > 360.f) {
            arc -= 360;
    }
    glutPostRedisplay();
    glutTimerFunc(200, update, 1);
}
int main(int argc, char** argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE  | GLUT_RGBA); //single buffer and RGBA
    glutInitWindowSize(600, 600);
    glutCreateWindow("Window");
    init();
    glutDisplayFunc(draw);
    glutTimerFunc(TIMERSECS, update, 1);
    glutKeyboardFunc(handleKeypress);
    glutMainLoop();
    return 0;
}

旋转始终相对于您使用的坐标系。变换总是以相反的顺序应用。当我们使用rotatef函数旋转对象时，它总是相对于坐标系的中心。因此，首先我们需要将其转换到由translatef(-300，-300,0)完成的中心。现在，对象位于中心。然后，我们使用rotatef将对象旋转到x，y或z轴。然后，我们再次将对象平移到转换之前的位置。最后，我们以相反的顺序编写函数。你已准备好出发 :)