mirror

[ch98]

Is it possible to put in an easy way to make mirror in mods in minetest? I hard that irrlicht can make mirrors and reflections. Maybe add a way of changing how much an surface reflects images with background texture so something like metal or water or glass can reflect a bit too.

[Exilyth]

There are three ways mirrors are done in games usually:

a) ray casting - light from the light sources (or rays from the camera, depending on which method is used) is cast through the world and is reflected off of surfaces (and takes on their color).

b) texture mirror - the camera is placed so that it views what the mirror would see. This view is saved as a texture and placed on the surface of the mirror. Downside: this requires one additional render pass per mirror.

c) fake - the mirror is a glass panel with a complete room placed behind it. All objects in the real room are copied in the mirror room.

Anyway, I doubt the low level rendering systems needed for either method a) or b) are made available through the lua api.
And c) might be hard to implement and/or give bad results.

[ch98]

There are three ways mirrors are done in games usually:

a) ray casting - light from the light sources (or rays from the camera, depending on which method is used) is cast through the world and is reflected off of surfaces (and takes on their color).

b) texture mirror - the camera is placed so that it views what the mirror would see. This view is saved as a texture and placed on the surface of the mirror. Downside: this requires one additional render pass per mirror.

c) fake - the mirror is a glass panel with a complete room placed behind it. All objects in the real room are copied in the mirror room.

Anyway, I doubt the low level rendering systems needed for either method a) or b) are made available through the lua api.
And c) might be hard to implement and/or give bad results.

I was suggesting of making new lua api for mirror surface in nodes.

[SegFault22]

I remember, when using that game making tool ''3D Rad'', there were options to make a surface of an object ''reflective''. 3D Rad is built in C++, which Minetest is built in, so it is possible. Maybe very, very difficult, but possible.

[hoodedice]

I remember, when using that game making tool ''3D Rad'', there were options to make a surface of an object ''reflective''. 3D Rad is built in C++, which Minetest is built in, so it is possible. Maybe very, very difficult, but possible.

Anything is possible. But implementing mirrors in a game which is by itself, largely buggy, unfinished and unoptimised is not nice.

[kaeza]

Anything is possible. But implementing mirrors in a game which is by itself, largely buggy, unfinished and unoptimised is not nice.

AFAIK, the problem with reflection is the fact that Minetest worlds are fully dynamic. In most other games, you can do those tricks because you "know" where the reflective surfaces are, and what can possibly be reflected on them and seen by the player because you have a closed, small environment.

Again, this is possible in Minetest, but not as trivial as in, say, a random FPS.

[ch98]

Anything is possible. But implementing mirrors in a game which is by itself, largely buggy, unfinished and unoptimised is not nice.

AFAIK, the problem with reflection is the fact that Minetest worlds are fully dynamic. In most other games, you can do those tricks because you "know" where the reflective surfaces are, and what can possibly be reflected on them and seen by the player because you have a closed, small environment.

Again, this is possible in Minetest, but not as trivial as in, say, a random FPS.

so we need an very good c++ programmer working on it long time?

[Exilyth]

Well... a basic ray/path tracing implementation isn't hard to write...

http://devmaster.net/posts/2836/raytracing-theory-implementation-part-1-introduction
http://www.codermind.com/articles/Raytracer-in-C++-Introduction-What-is-ray-tracing.html

... but it needs proper parallelisation and optimisation to run fast enough. And there can be artifacts/noise in the image when the camera moves, like this: http://www.youtube.com/watch?v=Dh9uWYaiP3s (the game shown, sfera, is open source btw)

I fear this might break the 'should run on low end machines' requirement of minetest.


So, something different...

Cheating with environment maps might be possible... They wouldn't give perfect reflections and would have to be recalculated every frame, but they might be fast enough to give the illusion of a mirror.
Mutltiple different techniques (+glsl shader code) are described e.g. here: http://www.ozone3d.net/tutorials/glsl_texturing_p04.php#part_4


If I wasn't busy learning for a test I'd go write a fork w/ray tracing.

[hdastwb]

This has been brought up before, but without much success: https://forum.minetest.net/viewtopic.php?id=1743

Texture mirroring seems like a pretty plausible feature to me, though it would probably only work well for small mirrors and on more powerful machines. One would probably have to adjust the camera location and FOV on each render pass, along with defining a certain render type which would mark mirror surfaces to the client and adding a player object for the mirror pass (unless Minetest players are actually secretly vampires).

so we need an very good c++ programmer working on it long time?

The devs have a tendency to shun actual C++ programmers; what you need is a novice who doesn't understand templates, iterators, inline functions, or RAII. You probably want a very good C programmer who knows very little C++ and can actually read through the Minetest codebase without wondering why the devs decided to redefine simple standard-library math functions and output operations for user-defined types as macros and who can read through the coding guidelines without wishing that they'd calmly overrun their calloc arrays and segfault out of existence sometime soon to be replaced with coding guidelines that, at the very least, do not encourage macros over templated inline functions or discourage the use of iterators or operator overloading for output of user-defined types.

I think it's pretty easy to figure out how to make a mirror and, assuming some basic reentrancy from the Minetest renderer, it shouldn't be too difficult to code up a basic implementation in the client. However, you'll probably have a hard time convincing any of the main devs to implement it, and any implementations from other people will likely never make it upstream. Thus, I think the addition of mirrors to Minetest is definitely a technical possibility but one that will probably never make it into the engine because of practicality reasons.

That said, I would like to be proved wrong because I would also really like to have mirrors in Minetest, but I am not going to put any time into coding it myself because I know far too much C++ and too little C to mess with the Minetest engine.