为什么我不能移动3D立方体？ OpenGL的

Question

My code is about creating 2 cubes, then rotating them at the same time, moving them at the same time, and scaling them at the same time. For rotating and scaling they work, but moving doesn't. I think it's something to do with my glTranslatef() but I tried all the ways I know.

The origin is the center of window and the cubes are always rotating.

Fragment Code:

    static GLfloat x = 0.0f;
    static GLfloat y = 0.0f;

    void display()
    {
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        glLoadIdentity();
        glTranslatef(-(1.5f + x), y + 0.5f, 0.3f);
        glScalef(xScale, yScale, zScale);
        glRotatef(theta[0], 1.0, 0.0, 0.0);
        glRotatef(theta[1], 0.0, 1.0, 0.0);
        glRotatef(theta[2], 0.0, 0.0, 1.0);
        colorcube();
        glFlush();

        glLoadIdentity(); 
        glTranslatef(1.5f + x, y + 0.5f, 0.3f);
        glScalef(xScale, yScale, zScale);
        glRotatef(theta[0], 1.0, 0.0, 0.0);
        glRotatef(theta[1], 0.0, 1.0, 0.0);
        glRotatef(theta[2], 0.0, 0.0, 1.0);
        colorcube();

        glFlush();
        glutSwapBuffers();
    }

    void spinCube()
    {
        // idle callback, spin cube 2 degrees about selected axis
        if (negative == true) theta[axis] -= 0.5;
        else  if (negative == false) theta[axis] += 0.5;
        if (theta[axis] > 360.0) theta[axis] -= 360.0;
        //display();
        glutPostRedisplay();
    }

void actionKeys(unsigned char key, int x, int y ) 
{
    switch (key)
    {
case 'r': case 'R': 
            x += 0.5f;
            glutPostRedisplay();
            break;
        case 'l': case 'L':
            x += 0.5f;
            glutPostRedisplay();
            break;
        case 'u': case 'U':
            y += 0.5f;
            glutPostRedisplay();
            break;
        case 'd': case 'D':
            y -= 0.5f;
            glutPostRedisplay();
            break;
}
}

Answer 1

The problem is with variable scope in your actionKeys function. You have global variables named x and y and the function parameters are also named x and y. Inside the actionKeys function the function parameter x and y are the ones that are being updated, not the global ones. This is why your movement doesn't work since the x and y global variables are never updated. I would suggest renaming the global variables to have a different naming convention than your function parameters so that you don't run into this problem again in the future. A common naming convention for global variables is to prefix them with g (for global) so you don't run into naming clashes with local variables.