OpenGL gluPickMatrix not existing

sandro4912

I tryed out a example for opengl which was for QT4. However now i use QT 5.12.4 and i get error with this command:

    gluPickMatrix(GLdouble(pos.x()), GLdouble(viewport[3] - pos.y()),
                  5.0, 5.0, viewport);

According from the web the Header QtOpenGL does not include anymore "OpenGL/glu.h" which is required for this command.

I tryed to include OpenGL/glu.h but it looks like it does not exist?

How can i add it. Im using KDE Neon (Linux).

SGaist

Hi,

IIRC this header comes from the glu library. On Debian it's the libglu1-mesa-dev package.

sandro4912

OK i could install it. But what else do i have to do that the project finds it?

SGaist

Taking a look at the package content, the header is under "GL/glu.h".

sandro4912

I added the header however its not found.

Steps i took:

sudo apt-get update
sudo apt-get install libglu1-mesa-dev

Restart the project and

#include "gl/glu.h"

SGaist

Casing is important.

sandro4912

Ok I changed it to the correct:

"GL/glu.h".

It looks like it is found. However when i compile i still get an error with the gluPickMatrix like this:

../tetrahedron/tetrahedron.cpp:128: undefined reference togluPickMatrix'
`

SGaist

You need to also link to libGLU.

wrosecrans

GLU was last updated in the 1990's, it's basically deprecated, and depends on functionality that was deprecated from OpenGL years ago. Ideally you should find a different way of doing what you are trying to accomplish. If you are using any kind of modern OpenGL with vertex shaders from the last ~15 - 20 years, GLU will have no idea how to understand your projection matrices, and the results it gives you will be nonsensical or wrong even if you get it working.

sandro4912

The whole code which uses the gluPickMatrix looks like this.

int Tetrahedron::faceAtPosition(const QPoint &pos)
{
    constexpr int MaxSize = 512;
    GLuint buffer[MaxSize];
    GLint viewport[4];

    makeCurrent();

    glGetIntegerv(GL_VIEWPORT, viewport);
    glSelectBuffer(MaxSize, buffer);
    glRenderMode(GL_SELECT);

    glInitNames();
    glPushName(0);

    glMatrixMode(GL_PROJECTION);
    glPushMatrix();
    glLoadIdentity();
    gluPickMatrix(GLdouble(pos.x()), GLdouble(viewport[3] - pos.y()),
                  5.0, 5.0, viewport);
    GLdouble x = GLdouble(width()) / height();
    glFrustum(-x, x, -1.0, 1.0, 4.0, 15.0);
    draw();
    glMatrixMode(GL_PROJECTION);
    glPopMatrix();

    if (!glRenderMode(GL_RENDER)) {
        return -1;
    }
    return static_cast<int>(buffer[3]);
}

What would be an alternative?

And how can i link against libGLU?

jsulm

@sandro4912 said in OpenGL gluPickMatrix not existing:

And how can i link against libGLU?
Add

LIBS += -lGLU

to your pro file.

sandro4912

The linking worked.

However i found this approach to implement gluPickMatrix and not need the glu library:

void gluPickMatrix(
        GLdouble x, GLdouble y, GLdouble deltax, GLdouble deltay,
        GLint viewport[4])
{
   if (deltax <= 0 || deltay <= 0) {
       return;
     }

   /* Translate and scale the picked region to the entire window */
   glTranslated((viewport[2] - 2 * (x - viewport[0])) / deltax,
           (viewport[3] - 2 * (y - viewport[1])) / deltay, 0);
   glScaled(viewport[2] / deltax, viewport[3] / deltay, 1.0);
}