opengl glDepthFunc不起作用 [英] opengl glDepthFunc doesn't work

问题描述

我正在编写显示对象隐藏部分的代码. 例如:板是较大的多边形对象，而圆柱是较小的多边形对象.圆柱体被板隐藏. (请参见下半部分窗口:圆柱体穿透了板.圆柱体的某些部分被板掩盖了.) 图片是由以下代码制作的.

I'm writing code that display hidden part of the object. Here is example : the plate is larger polygonal object, and cylinder is smaller polygonal object. cylinder is hidden by plate. (See the lower half window : cylinder penetrates the plate. some part of the cylinder is hidden by plate. ) The image is made by below code.

1. 绘制板(不将其绘制到RGB缓冲区.仅捕获深度值)
2. 绘制圆柱体(如果通过深度测试较少":则表示绘制了圆柱体的可见部分(深度较小))

每帧模型都沿y轴旋转.它为我提供了每帧正确的结果.

The model is rotated along y axis for each frame. It gives me a correct result for every frame.

现在，我想将圆柱体的隐藏部分显示为透明. 在使用混合之前，我只想显示圆柱的隐藏部分.也就是说，我必须显示圆柱区域，该区域的深度值比板的深度更大.然后，我改变

Now, I'd like to display hidden part of the cylinder as transparent. Before using blending, I want to display only the hidden part of the cylinder. That is, I have to display cylinder's region that have more greater depth values than plate's depth. Then, I just change

    glDepthFunc(GL_LESS); 

到

    glDepthFunc(GL_GREATER); 

但是，如果我将其更改为GL_GREATER，它不会给我正确的结果. 我在第一帧得到了正确的结果，但是之后，模型消失了. (这意味着该模型不会显示在窗口上.上下视口都显示) 我不明白原因.救救我！

However, If I changed it to GL_GREATER, it does not give me a correct result. I got correct result at first frame, but after then, the model is gone. (That means, the model is not displayed on window. Both of upper, and lower viewport) I cannot catch the reason. Help me!

void MyDisplay()
{
    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
    glRotatef(rot, 0, 1, 0);

    glViewport(0,0, width, height/2);
    glEnable(GL_DEPTH_TEST);
    DrawPlate();
    glColor4f(0,0,0,1);
    DrawCylinder();
    glDisable(GL_DEPTH_TEST);

    glViewport(0,height/2, width, height/2);
    glEnable(GL_DEPTH_TEST);

    glClearDepth(1.0);
    //glDrawBuffer(GL_NONE); // No color buffers are written
    glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE); 
    DrawPlate();

    glDepthFunc(GL_LESS); 
    // glDepthFunc(GL_GREATER); // doesn't work !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
    glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
    glColor4f(0,0,0,0.5f);
    DrawCylinder();

    delay(1);
    glFlush();
    glutPostRedisplay();
}

推荐答案

嘿，我找到了解决方案. 即:一帧后未初始化深度测试(更大). 帧后深度变为1，则没有像素通过测试. 因此，我必须在第一行输入glDepthFunc(GL_LESS).

Hey guys i found a solution. That is : depth test (greater) does not initialized after one frame. the depth goes to 1 after frame, then no pixel passes the test. Thus I have to input glDepthFunc(GL_LESS) at first line.

这篇关于opengl glDepthFunc不起作用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！