opengl 过剩旋转键盘方向

Question

我想制作一个小应用程序，让我可以将三角形移动到 top/bottm left/right。

当我按下 w -> 旋转并向上移动时，s => 旋转底部并移动底部，d -> 向右旋转并向右移动，a -> 向左旋转并向左移动..

这是我的代码：

#include <GL/glut.h> // (or others, depending on the system in use)
float xpoint1 = 0.0f;
float xpoint2 = 50.0f;
float xpoint3 = 25.0f;
float ypoint1 = 0.0f, ypoint2 = 0.0f, ypoint3 = 20.0f;
double direction = 0.0;
void Keys(unsigned char key, int x, int y) {

    if (key == 'a') {
        if (xpoint1 != 0) {
            xpoint1 -= 1.0f;
            xpoint2 -= 1.0f;
            xpoint3 -= 1.0f;
            direction = 90.0;
        }

    }
    else if (key == 'd') {
        if (xpoint2 != 200) {
            xpoint1 += 1.0f;
            xpoint2 += 1.0f;
            xpoint3 += 1.0f;
            direction = 270.0;
        }
    }
    else if (key == 'w') {
        if (ypoint3 != 150) {
            ypoint1 += 1.0f;
            ypoint2 += 1.0f;
            ypoint3 += 1.0f;
            direction = 0.0;
        }
    }
    else if (key == 's') {
        if (ypoint3 != 0) {
            ypoint1 -= 1.0f;
            ypoint2 -= 1.0f;
            ypoint3 -= 1.0f;
            direction = 180.0;
            
        }
    }
    
    glutPostRedisplay();
}
void resizeChange(int w, int h) {

    glClearColor(1.0, 1.0, 1.0, 0.0); // Set display-window color to white.
    glMatrixMode(GL_PROJECTION); // Set projection parameters.
    glLoadIdentity();
    gluOrtho2D(0.0, 200.0, 0.0, 150.0);
    glViewport(0, 0, w, h);
    glMatrixMode(GL_MODELVIEW);
}
void lineSegment(void)
{
    glClear(GL_COLOR_BUFFER_BIT); // Clear display window.
    glColor3f(0.0, 0.4, 0.2); // Set line segment color to green.
    
    //gluLookAt(0.0, 0.0, 5.0,
    //  0.0, 0.0,0.0,
    //  0.0, 1.0, 0.0
    //);

    glLoadIdentity();

    glRotated(direction, 0.0, 0.0, 1.0);
        glBegin(GL_TRIANGLES);
            glColor3f(1.0, 0.0, 0.0);
            glVertex2f(xpoint1, ypoint1);
            glColor3f(0.0, 1.0, 0.0);
            glVertex2f(xpoint2, ypoint2);
            glColor3f(0.0, 0.0, 1.0);
            glVertex2f(xpoint3, ypoint3);
        glEnd();
        //degree += 1.0;
    glFlush(); // Process all OpenGL routines as quickly as possible.
        //glutSwapBuffers();
}
void main(int argc, char** argv)
{
    glutInit(&argc, argv); // Initialize GLUT.
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); // Set display mode.
    glutInitWindowPosition(50, 100); // Set top-left display-window position.
    glutInitWindowSize(600, 600); // Set display-window width and height.
    glutCreateWindow("An Example OpenGL Program"); // Create display window.
    glutDisplayFunc(lineSegment); // Send graphics to display window.
    glutReshapeFunc(resizeChange);
    //glutIdleFunc(lineSegment);
    glutKeyboardFunc(Keys);
    glutMainLoop(); // Display everything and wait.
}

问题是当我尝试改变三角形的方向时它消失了？！ , 有什么问题吗?!

Answer 1

glRotated 围绕 (0, 0) 旋转。实际上旋转三角形看不见了。你必须先旋转三角形，然后将它移动到它在世界中的位置。不要改变顶点坐标，而是添加一个平移矩阵 glTranslate:

double tx = 0.0, ty = 0.0;
double direction = 0.0;

void Keys(unsigned char key, int x, int y)
{
    if (key == 'a') {
        tx -= 1.0;
        direction = 90.0;
    }
    else if (key == 'd') {
        tx += 1.0;
        direction = 270.0;
    }
    else if (key == 'w') {
        ty += 1.0;
        direction = 0.0;
    }
    else if (key == 's') {
        ty -= 1.0;
        direction = 180.0;
    }
    glutPostRedisplay();
}

void lineSegment(void)
{
    // [...]

    glTranslated(tx, ty, 0.0);
    glRotated(direction, 0.0, 0.0, 1.0);
    glBegin(GL_TRIANGLES);
            glColor3f(1.0, 0.0, 0.0);
            glVertex2f(-25.0, 0.0);
            glColor3f(0.0, 1.0, 0.0);
            glVertex2f(25.0, 0.0);
            glColor3f(0.0, 0.0, 1.0);
            glVertex2f(0.0, 20.0);
    glEnd();

    // [...]
}

opengl 过剩旋转键盘方向

opengl glut rotation keyboard directions

c++

opengl

glut

freeglut