如何在OpenGl中检查鼠标是否在屏幕的一侧？

#include <GL/glut.h>

int screenWidth = 800;
int screenHeight = 600;

void display()
{
    glClear(GL_COLOR_BUFFER_BIT);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(0, screenWidth, 0, screenHeight);

    glColor3f(1.0, 0.0, 0.0); // 设置颜色为红色

    // 获取鼠标的屏幕坐标
    int mouseX = glutGet(GLUT_WINDOW_WIDTH) / 2;
    int mouseY = glutGet(GLUT_WINDOW_HEIGHT) / 2;

    // 将屏幕坐标转换为OpenGL坐标
    float glX = (float)mouseX / screenWidth;
    float glY = (float)mouseY / screenHeight;

    // 检查鼠标是否在屏幕的一侧
    if (glX < 0.5) {
        // 鼠标在屏幕的左侧
        glBegin(GL_POLYGON);
        glVertex2f(0, 0);
        glVertex2f(screenWidth / 2, 0);
        glVertex2f(screenWidth / 2, screenHeight);
        glVertex2f(0, screenHeight);
        glEnd();
    } else {
        // 鼠标在屏幕的右侧
        glBegin(GL_POLYGON);
        glVertex2f(screenWidth / 2, 0);
        glVertex2f(screenWidth, 0);
        glVertex2f(screenWidth, screenHeight);
        glVertex2f(screenWidth / 2, screenHeight);
        glEnd();
    }

    glFlush();
}

int main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize(screenWidth, screenHeight);
    glutCreateWindow("OpenGL Mouse Check");
    glutDisplayFunc(display);
    glutMainLoop();
    return 0;
}