如何在OpenGL中一起绘制2D和3D东西？

Question

如何在OpenGL中一起绘制2D和3D东西？如果可能的话,请给我看一些C++代码.请展示如何在3D对象后面和前面绘制.

Answer 1

关于这个方式:

void render_perspective_scene(void);

void render_ortho_scene(void);

void render_HUD();

void display()
{
    float const aspect = (float)win_width/(float)win_height;

    glViewport(0,0,win_width,win_height);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glFrustum(-aspect*near/lens, aspect*near/lens, -near/lens, near/lens, near, far);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    render_perspective_scene();

    // just clear the depth buffer, so that everything that's
    // drawn next will overlay the previously rendered scene.
    glClear(GL_DEPTH_BUFFER_BIT);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(-aspect*scale, aspect*scale, -scale, scale, 0, 1);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    render_ortho_scene();

    // Same for the HUD, only that we render
    // that one in pixel coordinates.
    glClear(GL_DEPTH_BUFFER_BIT);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0, win_width, 0, win_height, 0, 1);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    render_HUD();
}

Answer 2

您处于正确的轨道上但是在绘制2D图形时还必须禁用深度测试: glDisable(GL_DEPTH_TEST);

否则它可能会被您的3D图形隐藏.