c - 在窗口 OpenGL 中一起打印变量和多边形

Question

我正在尝试在 OpenGL 的 Canvas 上打印一行包含一个变量和一个点的文本。我的代码如下:

 void display()
 {
    glClear (GL_COLOR_BUFFER_BIT);
    glLoadIdentity();
    char string[50];
    sprintf(string, "Base Rotation: %d", numVertices); 
    renderMyText(-0.4, 0.35, string);
    glPointSize(20);
    glBegin(GL_POINTS);
        glVertex2f(characterX, characterY);
    dx = vertices[numVertices-1].x-ox;
    dy = vertices[numVertices-1].y-oy;
    dt = glutGet(GLUT_ELAPSED_TIME);
    characterX = ox + dx / sqrt(dx*dx+dy*dy) * Velocity * dt;
    characterY = oy + dy / sqrt(dx*dx+dy*dy) * Velocity * dt;
    printf("%f %f", characterX, characterY); 
    glEnd();
    glFlush();
}

我正在使用一种不同的方法来在鼠标移动时更新点的位置。该代码一切正常，正方形更新了它的位置并完美移动，直到我添加了文本行。

现在发生的情况是，一旦我启动程序，方 block 和文本就会出现，但是一旦我在窗口中移动鼠标，方 block 就会消失，只剩下文本，我希望它们两个留在窗口中。谁能看出哪里出了问题？

Answer 1

我解决了这个问题，所以我觉得我应该添加解决方案:

我以错误的方式解决了这个问题，我应该像这样在空闲方法中更新我的坐标值:

    void idle()
{
    //dx is last mouse x - last box x
    dx = vertices[numVertices-1].x-ox;
    //dy is last mouse y - last box y
    dy = vertices[numVertices-1].y-oy;
    dt = 50;
    //dt helps to control the chasing charcters speed
    characterX = ox + dx / sqrt(dx*dx+dy*dy) * Velocity * dt;
    characterY = oy + dy / sqrt(dx*dx+dy*dy) * Velocity * dt;
    //equations to move the character after the cursor by moving it along the slope of the line between the two points
    ox = characterX;
    oy = characterY;
    //update object x and y for next calculation
    if((numVertices > 5) && characterX >= vertices[numVertices-1].x - 1 && characterX <= vertices[numVertices-1].x + 1 && characterY >= vertices[numVertices-1].y -1 && characterY <= vertices[numVertices-1].y + 1) { 
        endGame = true;
        //vertices over 5, so that we don't accidentially die when we start, this collision detection code works on a threshold of contact of one
        //between the cursor and object on the X and Y
    }
    glutPostRedisplay();
}

然后 glutPostRedisplay 调用显示方法，我在这里使用坐标计算来更改点在屏幕上的位置:

        void display() { 
            glColor3f(0,255,0); //set the in game text to green
            if(endGame == true) { 
                glColor3f(255,0,0);
                //if the game is over set the text to red
            }
            glClear (GL_COLOR_BUFFER_BIT);
            glPointSize(20);
            glBegin(GL_POINTS);
                glVertex2f(characterX, characterY);
            glEnd();
            glFlush();
            glutSwapBuffers();
}