GlReadPixels始终取自深度缓冲区0

Question

情况是，有许多相交的表面，并且无需单击鼠标即可确定光标位置的实际坐标（如果它指向的是什么或表面），为此，我想使用glReadPixels ，在整个着色器上绘制，最终glReadPixels给我当前像素的深度始终等于0 ，因为这可能是这样，并且可能具有新版opengl的替代功能中的任何功能，在论坛上寻找信息，但是发现我可以帮助，在此先感谢。

Answer 1

As far as I understood the question, you want to find coordinates of interscetion of some objects. Correct?

You can't do any of these with glReadPixels, because this fuction returns color of pixel. Pixels are flat (as your computer screen is), so there is no depth written. It just gets info from the result image on the screen.

Here is nice quote: "OpenGL is not a scene management library. It is just a drawing API that draws things onto the screen and then forgets about them."

So my guess is that you would have to do some tricks in your code and calculate everything with your own functions according to how your code works.

Answer 2

I am writing in Qt using openGl a 3D widget, which displays a variety of objects. It is necessary to find the coordinates of the point (which of course will be on-site) under the cursor, if it points to the coca-object respectively. All rendering goes through shaders. I want to get the depth value of the depth buffer in a given pixel, a lot of which shows how to do this, and I do the same, but glReadPixels always tells me that the depth of any pixel is 0.

enter code here

initializeOpenGLFunctions();

glEnable(GL_TEXTURE_2D);

//корректное отображение перспективы
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);

glEnable(GL_ALPHA_TEST);
glAlphaFunc(GL_GREATER,0);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glEnable(GL_BLEND);

// включение обновление буфера глубины
glEnable(GL_DEPTH_TEST);

// очистка буфера
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

GLint viewport[4];
GLdouble modelview[16];
GLdouble projectionmtr[16];
GLfloat winX, winY, winZ;
GLdouble posX, posY, posZ;

viewport[0] = 0;
viewport[1] = 0;
viewport[2] = geometry().width();
viewport[3] = geometry().height();
QMatrix4x4 mtr =  mCameraMatr * mObjectMatr * mScale * mCentrTr * translate;

int k = 0;
for(int i = 0; i<4; ++i)
{
    for(int j = 0; j<4; ++j)
    {
        modelview[k] = mtr(j,i);
        ++k;
    }
}

k = 0;
for(int i = 0; i<4; ++i)
{
    for(int j = 0; j<4; ++j)
    {
        projectionmtr[k] = projection(j,i);
        ++k;
    }

winX = x;
winY = viewport[3] - y;

glReadPixels( x, int(winY), 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &winZ );// Here is always written in the variable winZ 0

gluUnProject( winX, winY, winZ, modelview, projectionmtr, viewport, &posX, &posY, &posZ);

return QVector3D(posX, posY, posZ);