convert_shader_to_harfang.md

Convert SHADERTOY shader to HARFANG® API

In order to see if GLSL is portable in BGFX GLSL or BGFX HLSL, we decided to use a Shadertoy shader (that is using GLSL) and make it viable in HARFANG API (which is using BGFX)

In GLSL you can do this *= but not in HLSL so we are moving

• from this :

      p.xz *= _dt;

• to this :

      p.xz = mul(_dt, p.xz);

• or :

      p.xz = p.xz * _dt;

In GLSL you can do vec2(0.2) and it declares both values of the vec2. So we are moving

• from this :

      myVec2 = vec2(0.2);

• to this :

      myVec2 = vec2(0.2, 0.2);
  

In GLSL you can return struct but not in HLSL. So we are moving

• from this :

  struct obj
  {
      float d;
      vec3 cs;
      vec3 cl;
  }
  
  obj prim1(vec3 p)
  {
      p.x = abs(p.x)-3.;
      float per = 0.9;
      float id = round(p.y/per);
      p.xz *= rot(sin(dt(0.8,id*1.2)*TAU));
      crep(p.y, per,4.);
      mo(p.xz,vec2(0.3));
      p.x += bouncy(2.,0.)*0.8;
      float pd = box(p,vec3(1.5,0.2,0.2));
      return obj(pd,vec3(0.5,0.,0.),vec3(1.,0.5,0.9));
  }

• to this :

  struct obj
  {
      float d;
      vec3 cs;
      vec3 cl;
  }
  
  obj prim1(vec3 p)
  {
      p.x = abs(p.x)-3.0;
      float per = 0.9;
      float id = round(p.y/per);
      mat2 _dt = rot(sin(dt(0.8,id*1.2)*TAU));
      p.xz = mul(_dt, p.xz); 
      crep(p.y, per,4.0);
      mo(p.xz,vec2(0.3, 0.3));
      p.x += bouncy(2.0,0.0)*0.8;
      float pd = box(p,vec3(1.5,0.2,0.2));
  
      obj result; 
      result.d = pd;
      result.cs = vec3(0.5, 0.0, 0.0);
      result.cl = vec3(1.0, 0.5, 0.9);
      return result;
  }

In native GLSL you can have all types of uniforms but not with BGFX GLSL or BGFX HLSL,

So we are moving

• from this

      uniform float x;

• to this

      uniform vec4 (x, ~, ~, ~);

"~" are random values.