Attachment 117920 Details for Bug 91114 – GLSL sample implementaton of compute LOD for textureGradient of cubemaps

GLSL sample implementaton of compute LOD for textureGradient of cubemaps

textureCubeLOD.glsl (text/plain), 2.48 KB, created by Kevin Rogovin on 2015-08-26 07:14:32 UTC

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Creator: Kevin Rogovin

Created: 2015-08-26 07:14:32 UTC

Size: 2.48 KB

patch

obsolete

>
>/* Output:
>     q is p reorded so that the component with the largest magnitude
>     is in the z-coordinate. In addition dqdx and dqdy are the reorderings
>     of dpdx and dpdy to mirror the reordering in q.
> */
>void
>compute_selector_fast_and_brave(in vec3 p, in vec3 dpdx, in vec3 dpdy,
>				out vec3 q, out vec3 dqdx, out vec3 dqdy)
>{
>  vec3 absP;
>  float m;
>
>  absP = abs(p);
>  m = max(absP.x, max(absP.y, absP.z));
>  if (m == absP.x)
>    {
>      q = p.yzx;
>      dqdx = dpdx.yzx;
>      dqdy = dpdy.yzx;
>    } 
>  else if (m == absP.y)
>    {
>      q = p.xzy;
>      dqdx = dpdx.xzy;
>      dqdy = dpdy.xzy;
>    }
>  else
>    {
>      q = p;
>      dqdx = dpdx;
>      dqdy = dpdy;
>    }
>}
>
>void
>compute_selector_slow_and_careful(in vec3 p, in vec3 dpdx, in vec3 dpdy,
>				  out vec3 q, out vec3 dqdx, out vec3 dqdy)
>{
>  vec3 absP;
>  float m;
>
>  absP = abs(p);
>  if (absP.x >= max(absP.y, absP.z))
>    {
>      q = p.yzx;
>      dqdx = dpdx.yzx;
>      dqdy = dpdy.yzx;
>    } 
>  else if (absP.y >= max(absP.x, absP.z))
>    {
>      q = p.xzy;
>      dqdx = dpdx.xzy;
>      dqdy = dpdy.xzy;
>    }
>  else
>    {
>      q = p;
>      dqdx = dpdx;
>      dqdy = dpdy;
>    }
>}
>
>
>/* Choose the compute_selector method
> */
>#ifdef FAST_AND_BRAVE
>#define compute_selector compute_selector_fast_and_brave
>#else
>#define compute_selector compute_selector_slow_and_careful
>#endif
>
>void
>compute_vec2s(in vec3 q, in vec3 dqdx, in vec3 dqdy,
>	      out vec2 uv, out vec2 duvdx, out vec2 duvdy) 
>	      
>{
>  float recip, common;
>
>  recip = 1.0 / q.z;
>  common = recip * recip
>
>  uv.xy = q.xy * recip;
>  duvdx = dqdx * recip - q.xy * (dqdx.z * common);
>  duvdy = dqdy * recip - q.xy * (dqdy.z * common);
>}
>
>/* given position and derivatives of position
>   compute the LOD for a cubemap texture look
>   up where the dimension of the cubemap is L
> */
>float
>compute_textureCubeLOD(in vec3 p, in vec3 dpdx, in vec3 dpdy,
>		       in float L)
>{
>  vec3 q, dqdx, dqdy;
>  vec2 uv, duvdx, duvdy;
>  float m;
>
>  compute_selector(p, dpdx, dpdy, q, dqdx, dqdy);
>  compute_vec2s(q, dqdx, dqdy, uv, duvdx, duvdy);
>
>  m = max(dot(duvdx, duvdx), dot(duvdy, duvdy));
>
>  /*
>     rho = 0.5 * L * max( ||duvdx||, ||duvdy||)
>         = 0.5 * L * sqrt( max(dot(duvdx, duvdx), dot(duvdy, duvdy)) )
>	 = 0.5 * sqrt(L * L * m)
>
>     LOD = log2(rho)
>         = log2(0.5 * sqrt(L * L * m) ); 
>	 = -1.0 + 0.5 * log2(L * L  *m);
>  
>   */
>  return -1.0 + 0.5 * log2(m * L * L);
>  
>}

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Attachments on bug 91114: 116726 | 116781 | 116782 | 117920 | 117921

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