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Comment by Sharlin | Hacker News Reader

I mean, it wouldn't be DOOM if it weren't raycast :)

I'm actually surprised that this wasn't just running (a port of) the original DOOM engine – or maybe it does, at least the renderer? I don't know if that's possible with Construct.

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Doom doesn't use raycasting, it uses binary space partitioning.

From the description it seems to be a DOOM clone. Physics feels a bit off, but all the little details may trick you into believing that it's the real thing.

Doom uses both: binary space partitioning to find the visible surfaces then casting rays to draw the textures.

It doesn't. Doom uses BSP to precisely determine which columns of textures it needs to render.

It's faster than raycasting, so this was even used in Wolf3D port to GBA.

Yeah is fast and cheap because the BSP tree is created after the level mapped out. It's also why "Will it run DOOM?!" is a thing.

For further reading: https://en.wikipedia.org/wiki/Doom_engine#Binary_space_parti... https://en.wikipedia.org/wiki/Binary_space_partitioning#Appl...

There is no need to cast rays when you have divided the space into convex polygons. If you know all the vertices of a convex polygon and two of them form a visible wall, you can determine the texture column and height of the screen space wall column by means of interpolation. This is what the Doom engine does.

The PC version of Wolfenstein 3D used a more straight forward ray casting approach, but I think the SNES port was Id's first use of BSP.

An easy tell is walking up to a painting or even looking at the pillars you see from your starting position: you'll notice that the vertical lines aren't perfectly perpendicular to the horizontal lines in screen space, because the camera is pointed slightly upwards. In Doom, walls are rendered as strips of screen columns, and the pitch of the camera angle looks like it's perfectly parallel to the horizontal plane as a result.

You can sort of implement looking up and down with minor modifications to the Doom engine, and this was implemented in Heretic, but because of the nature of the renderer, vertical lines in the world remain vertical lines in screen space even when you pitch the camera, so it looks somewhat distorted in a way that's very characteristic of the post-Doom "2.5D" engines.

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