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Thread: GLM::ORTHO reverts Y-axis. Why?

  1. #1
    Junior Member Newbie
    Join Date
    Feb 2018

    Question GLM::ORTHO reverts Y-axis. Why?

    I'm using GLM library. And when I initialize orthographic perspective the Y-axis gets reverted, the positive becomes down. How do I revert it so that the positive is up but still use glm:rtho? Thanks.
    Code :
    glm::mat4 projection_mat = glm::ortho((float)leop_opengl_window.getWidth()*-1.0f, (float)leop_opengl_window.getWidth(), (float)leop_opengl_window.getHeight(), (float)leop_opengl_window.getHeight()*-1.0f);

  2. #2
    Senior Member OpenGL Guru Dark Photon's Avatar
    Join Date
    Oct 2004
    Swap your bottom and top arguments.

    In OpenGL, the Y axis points up (in eye space and NDC space). So your bottom should be less than your top, unless you intentionally want to flip the orientation vertically.


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