I’m trying to access the z or depth value at a point clicked by the mouse using glReadPixels(), and am getting a nonsensical value returned.

glGetIntegerv(GL_VIEWPORT, viewport);

glGetDoublev(GL_MODELVIEW_MATRIX, modelMatrix);

glGetDoublev(GL_PROJECTION_MATRIX,projMatrix);

realy = viewport[3] - (GLint) point.y - 1;

glReadPixels(x, realy, 1, 1, GL_DEPTH_COMPONENT, GL_DOUBLE, &winz);

```
gluUnProject((GLdouble)point.x, (GLdouble)realy, winz, modelMatrix,
projMatrix, viewport, &objx, &objy, &objz);
```

The value returned for winz is consistently -9.25596e+061. A number which I don’t understand!

This doesn’t make any sense, since there is a polygon object right below the mouse where I click to test for depth.

Anyone know what I might be doing wrong here?