How to scale 2d world with 3d rendering?

Question

I'm using 3d mode to render my 2d game, because the camera rotation and zooming in/out is much easier than with 2d mode.

Now i have ran into a problem i cant seem to think how to fix:

• How to make the 2d plane of my world to fit the screen in a way that 1 texture pixel matches 1 pixel on my screen? In other words: how do i calculate the z-position of my camera to achieve this?

My texcoords start from 0 and ends to 1, so i can see all the pixels from one tile in the GL_NEAREST texture filter mode.

My window is resizeable in a way that my tiles are always squares but the visible area expands depending on how i resize my window.

Edit: my view port is using perspective mode, not isometric. but if its not possible in perspective mode, im willing to change to isometric.

Answer 1

Use an orthographic projection that maps eye space units to pixels:

glViewport(0,0, width, height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0, width, 0, height, -1, 1);

Update due to question update:

A texel → viewport pixel matching is possible with a perspective projection, but only under a certain constraint: The textured quad must be coplanar to the perspective frustum near/far plane.

How to do it? For glFrustum(left, right, bottom, top, near, far) with Z=near, XY eye space range [left, right]×[bottom, top] maps to NDC xy[-1, 1]² and NDC xy[-1, 1]² maps to the viewport extents. So those are all affine transformations following the law

y(x) = to_lower_bound + (x - from_lower_bound) * (to_upper_bound - to_lower_bound) / (from_upper_bound - from_lower_bound)

All you have to do it map viewport to NDC to near plane and if you're Z =/= near scale by near/Z.