How does one make a 3D background in a 2D game?

Question

I am trying to figure out how to make a background that looks 3D in a game that is 2D. Below there is a video of the game "Under The Lotus." I am trying to get a background with similar effect (it looks like a 3D environment, while the game runs basically in the X and Y axis).

http://www.youtube.com/watch?v=3GsTwsx5aWo

Can anyone give me an idea how to do that? Or point me in some direction on what to read to be able to figure this out?

I am planning on using SDL for this game. If I could avoid using OpenGL that would be better, but it is not a real requirement.

Answer 1

Like chrish said, I would recommend writing a game in a 3D engine or with a 3D framework than working with a 2D engine or framework and trying to add in 3D just for a single effect. OpenGL can do it, and so can many other game engines, like Unity (I would assume) and the BGE.

Answer 2

A lot of 2D games are actually written using OpenGL (which is still a good option with SDL, actually); you can take advantage of the 3D hardware for creating very nice special effects without impacting your draw performance.

In a case like this, you'd draw your 3D background, switch to an orthographic projection, then draw your 2D bits on top. If I remember correctly, glOrtho() sets up the projection you want, and should be enough info to get you going (finding ortho tutorials is as simple as hitting up the Google). For example, NeHe's Tutorial 21 shows you how to use glOrtho() for drawing 2D objects.

Answer 3

As others have said, using OpenGL/DirectX will give you more options and better performance for most things. It's definitely a lot more complex than SDL, but it will pay off.

The particular effect looks a pixel shader that uses noise (probably multiple times - first to find the coordinates in the noise, then to find the value). I was able to achieve a similar effect with this (HLSL, sorry):

sampler sNoise = sampler_state { texture = <_noise>; magfilter = ANISOTROPIC; minfilter = ANISOTROPIC; mipfilter = ANISOTROPIC; AddressU = MIRROR; AddressV = MIRROR; };
sampler sColors = sampler_state { texture = <_colors>; magfilter = ANISOTROPIC; minfilter = ANISOTROPIC; mipfilter = ANISOTROPIC; AddressU = BORDER; AddressV = BORDER; };

float4 background(PixelInfo p) : COLOR0
{
    float3 ofs = _time * _velocity + _ofs;
    float3 spos = float3((p.uv - ofs.xy) * 512 / _screenSize, ofs.z);

    float3 vpos;
    vpos.x = tex3D(sNoise, spos + 0.0000).r - 0.5;
    vpos.y = tex3D(sNoise, spos + 0.3333).r - 0.5;
    vpos.z = tex3D(sNoise, spos + 0.6667).r - 0.5;

    float v = tex3D(sNoise, vpos).r;
    return tex1D(sColors, pow(v, _density));
}