レイマーチングテスト

RayMarching.rb

require 'dxruby'

hlsl = <<EOS
  float4x4 g_proj, g_view;

  struct VS_INPUT // 頂点シェーダの入力フォーマット
  {
    float4 vPosition    : POSITION0;
    float2 vTexCoord    : TEXCOORD0;
  };

  struct VS_OUTPUT // 頂点シェーダの出力フォーマット
  {
    float4 vPosition    : POSITION0;
    float2 vTexCoord    : TEXCOORD0;
  };

  VS_OUTPUT VS(VS_INPUT v) // 頂点シェーダ
  {
    VS_OUTPUT output;
    output.vPosition = mul(mul(v.vPosition, g_view), g_proj);
    output.vTexCoord = v.vTexCoord;
    return output;
  }

  struct PS_INPUT
  {
    float2 vTexCoord  : TEXCOORD0;
  };

  struct PS_OUTPUT
  {
    float4 vColor    : COLOR0;
  };

  float3 mod(float3 a, float b) { return a-b*floor(a/b); }

  float DistanceFunction(float3 pos)
  {
    float c = 8.0;
    return length(mod(pos, c) - 0.5 * c) - 1.0;
  }

  float3 getNormal(float3 p)
  {
    float d = 0.0001;
    return normalize(float3( DistanceFunction(p+float3(d,0.0,0.0))-DistanceFunction(p+float3(-d,0.0,0.0)),
                             DistanceFunction(p+float3(0.0,d,0.0))-DistanceFunction(p+float3(0.0,-d,0.0)),
                             DistanceFunction(p+float3(0.0,0.0,d))-DistanceFunction(p+float3(0.0,0.0,-d))));
  }

  PS_OUTPUT PS(PS_INPUT p)
  {
    PS_OUTPUT output;
    float2 pos = (p.vTexCoord * 2.0 - 1.0) * float2(640.0 / 480.0, -1.0);
    float3 light = float3(1, 1, -1);

    float3 camPos = float3(0.0, 0.0, -3.0);
    float3 camDir = float3(0.0, 0.0, 1.0);
    float3 camUp = float3(0.0, 1.0, 0.0);
    float3 camSide = cross(camUp, camDir);
    float focus = 1.8;
 
    float3 rayDir = normalize(camSide*pos.x + camUp*pos.y + camDir*focus);
 
    float t = 0.0, d;
    float3 posOnRay = camPos;
 
    for(int i=0; i<32; ++i)
    {
      d = DistanceFunction(posOnRay);
      t += d;
      posOnRay = camPos + t*rayDir;
    }
 
    if(abs(d) < 0.001)
    {
      float3 normal = getNormal(posOnRay);
      output.vColor = float4(float3(1,1,1) * max(dot(normal, light), 0.2),1);
    }
    else
    {
      output.vColor = float4(0,0,0,0);
    }
    return output;
  }

  technique
  {
  pass
    {
      VertexShader = compile vs_3_0 VS();
      PixelShader = compile ps_3_0 PS();
    }
  }
EOS

width = 640
height = 480

core = Shader::Core.new(hlsl,
                    g_view: :float,
                    g_proj: :float)
shader = Shader.new(core)

# 2D用ビュー行列
shader.g_view = [       1,        0, 0, 0,
                        0,       -1, 0, 0,
                        0,        0, 1, 0,
                 -width/2, height/2, 0, 1]

# 2D用透視変換(?)行列
shader.g_proj = [2.0 / width,            0, 0, 0,
                           0, 2.0 / height, 0, 0,
                           0,            0, 0, 0,
                           0,            0, 1, 1]

image = Image.new(640, 480)

Window.loop do
  Window.draw_shader(0, 0, image, shader)
  break if Input.key_push?(K_ESCAPE)
end