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Soft blurry shadow in ParallaxOcclusionMapping


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#1 Jeason   Members   -  Reputation: 96

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Posted 06 March 2012 - 12:17 AM

Greeting!

I am learning ParallaxOcclusionMapping recently, but i get in trouble now.
I can't comprehend the following codes well which are found in ParallaxOcclusionMapping sample in DX9.
Is there any theory or basis behind the codes, especially the number and weight, such as 0.88, 0.77, 0.66?

if ( g_bDisplayShadows == true )
  {
   float2 vLightRayTS = vLightTS.xy * g_fHeightMapScale;
   // Compute the soft blurry shadows taking into account self-occlusion for
   // features of the height field:
   float sh0 =  tex2Dgrad( tNormalHeightMap, texSampleBase, dx, dy ).a;
   float shA = (tex2Dgrad( tNormalHeightMap, texSampleBase + vLightRayTS * 0.88, dx, dy ).a - sh0 - 0.88 ) *  1 * g_fShadowSoftening;
   float sh9 = (tex2Dgrad( tNormalHeightMap, texSampleBase + vLightRayTS * 0.77, dx, dy ).a - sh0 - 0.77 ) *  2 * g_fShadowSoftening;
   float sh8 = (tex2Dgrad( tNormalHeightMap, texSampleBase + vLightRayTS * 0.66, dx, dy ).a - sh0 - 0.66 ) *  4 * g_fShadowSoftening;
   float sh7 = (tex2Dgrad( tNormalHeightMap, texSampleBase + vLightRayTS * 0.55, dx, dy ).a - sh0 - 0.55 ) *  6 * g_fShadowSoftening;
   float sh6 = (tex2Dgrad( tNormalHeightMap, texSampleBase + vLightRayTS * 0.44, dx, dy ).a - sh0 - 0.44 ) *  8 * g_fShadowSoftening;
   float sh5 = (tex2Dgrad( tNormalHeightMap, texSampleBase + vLightRayTS * 0.33, dx, dy ).a - sh0 - 0.33 ) * 10 * g_fShadowSoftening;
   float sh4 = (tex2Dgrad( tNormalHeightMap, texSampleBase + vLightRayTS * 0.22, dx, dy ).a - sh0 - 0.22 ) * 12 * g_fShadowSoftening;
   // Compute the actual shadow strength:
   fOcclusionShadow = 1 - max( max( max( max( max( max( shA, sh9 ), sh8 ), sh7 ), sh6 ), sh5 ), sh4 );
   // The previous computation overbrightens the image, let's adjust for that:
   fOcclusionShadow = fOcclusionShadow * 0.6 + 0.4;		
  }   


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#2 Dawoodoz   Members   -  Reputation: 299

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Posted 06 March 2012 - 03:38 AM

If I understand it correct, the values are creating a height sampling line from the light direction in tangent space.

My open source DirectX 10/11 graphics engine. https://sites.google.com/site/dawoodoz

"My design pattern is the simplest to understand. Everyone else is just too stupid to understand it."


#3 Jeason   Members   -  Reputation: 96

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Posted 06 March 2012 - 07:47 PM

Yes, you are right, Dawoodoz.

But what i want to know is why author use this method to calculate the soft shadow factor? Does he take some theories into the above formula?




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