Mixed intrinsic and extrinsic camera parameter in OpenGL projection matrix

[zhengpingzhou]

Bug Report

• I checked the documentation and the forum but found no answer.
• I checked to make sure that this issue has not already been filed.

Environment

• DART version: 6.3.0
• OS name and version name(or number): Ubuntu 18.04
• Compiler name and version number: GCC 7.5.0

Expected Behavior

The OpenGL projection matrix is expected to have the following structure:

Therefore, if you print the value of GL_PROJECTION_MATRIX, the 16th element must be zero.

Current Behavior

Currently, if you construct a SimWindow following the default setup, the 16th element of GL_PROJECTION_MATRIX is not zero. For example, when the aspect ratio is 4:3, the projection matrix is:

 1.81066        0        0        0
       0  2.41421        0        0
       0        0  -1.0202 0.818182
       0        0       -1        1

It seems the cause of the problem is that part of extrinsic parameters (which are supposed to be included in the model-view matrix) are integrated into the projection matrix (which is supposed to only contain the intrinsic parameters):

https://github.com/dartsim/dart/blob/v6.3.0/dart/gui/Win3D.cpp#L169

This may lead to confusion if the camera parameters need to be exported and used in other programs. Although this does not expose any rendering problem, I personally suggest moving the gluLookAt to model-view. Kindly let me know if I'm missing any context.

Code to Reproduce

dart-opengl-projection-matrix-bug-report

Steps to Reproduce

Build and run the code. The code prints the value of GL_PROJECTION_MATRIX when the aspect ratio is 4:3.

[jslee02]

Thanks for the report with the test code! I was able to reproduce the incorrect projection matrix computation and fix it by moving the gluLookAt to the model-view section, as you suggested (#1485).

[zhengpingzhou]

Great, thanks!