How to Draw Scaled Single-Pixel Lines with OpenGL?

Draw Scaled Single-Pixel Lines with OpenGL

Problem:

When rendering a 320x240 OpenGL scene scaled to a higher resolution (e.g., 960x720), lines appear thinner than intended due to being drawn on the scaled output canvas instead of the internal 320x240 canvas.

Answer:

The misunderstanding lies in the assumption that there is a separate 320x240 OpenGL canvas. The entire viewport is the physical window resolution (960x720 in this case).

Solution:

To draw pixelated lines at the correct thickness, the rendering should be performed to a separate 320x240 image buffer, and then the image should be drawn to the screen as a scaled texture.

Steps:

1. Create a 320x240 texture.
2. Create a framebuffer object (FBO) and attach the texture to it.
3. Bind the FBO for rendering.
4. Set the viewport to the image size (320x240).
5. Render the scene to the FBO.
6. Unbind the FBO.
7. Set the viewport to the window size (960x720).
8. Draw the texture to the window as a scaled image.

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