Question

我试图在OpenGL的画布上打印一行包含变量和点的文本。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();
}

我使用不同的方法在鼠标移动时更新点位置。该代码一切正常，方块更新了它的位置并完美移动，直到我添加了文本行。

现在发生的事情是，一旦我启动程序，方形和文本出现，但是一旦我在窗口中移动鼠标，方块消失，只有文本保留，我希望它们中的两个留在窗口中。谁能看到什么错了？

Answer 1

我解决了这个问题所以我觉得我应该添加解决方案：

我是以不正确的方式解决这个问题，我应该在空闲方法中更新我的坐标值，如下所示：

    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display方法，我在这里使用坐标计算来改变屏幕上Point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();
}

在OpenGL窗口中打印变量和多边形

1 个答案: