Drawing a 3D cuboid and rotating it in OpenGL

Question

I am trying to draw a 3D cuboid by clicking on one of the corner points and then extending it based on the dimensions provided by the user, and then rotating it about any axis. However, I am not sure about how I can specify the (x, y, z) tuple after the mouse-click, since the output window is on 2D. Also, I cannot understand how to extend the point to form a cuboid.

Answer 1

What you want is called 3D Picking. Usually, this is done using Raycasting.

However, there is an easy solution (with acceptable performance) that involves rendering the scene off-screen on a framebuffer with 32-bit floats for the R/G/B values.

In the shader you use the x, y and z coordinates of that pixel as the color values.

Then, when the user clicks somewhere, you simply read out that pixels color to get its position.