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xujiezhige

soft shadow in ParallaxOcclusionMapping

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I get the codes in ParallaxOcclusionMapping sample in DX9.
Is there any theory or basis behind the codes, especially the number and weight ?

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;


Please help me!

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