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Editorial Team
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Asked: 2026-06-16T12:44:46+00:00

I have a 3D scene I’m drawing and I want to draw a rectangle

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I have a 3D scene I’m drawing and I want to draw a rectangle for a dialogue text that will be stretched for all the screen’s width, what’s the best way to achieve this, having performance in mind?

I found about glOrtho() that I can use for exact pixel placing, but since it’s a matrix multiplication task, won’t my app feel much heavier during scenes with dialogues?
If yes, should I try to find a math solution to find the X position of my left window corner according to some Z distance and draw a QUAD from there? (Is this even possible?)

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1 Answer

  1. Editorial Team

    glOrtho() is the way to go.

    In the course of OpenGL’s rendering Pipeline, during the Primitive Assembly stage, every vertex will be transformed (projected) from eye coordinates to clip coordinates. Whether your projection matrix is used for 3D perspective or 2D orthogonalization, it’s still one matrix multiplication per vertex before Rasterization starts.

    glOrtho() will change your projection matrix to an orthographic one but the matrix only needs to be generated once per frame and the equations required to do so are very simple:

    enter image description here

    (image credit: MSDN)

    Once you have a projection matrix, don’t let the thought of matrix multiplication scare you. It’s exactly what video cards are designed to do and it’s hardly a frightening task for any processor or GPU these days.

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