Queried Virtual Shadow Maps problem

akira32

I am implementing the QVSM.
I have a question how to calculate the matrix of m4x4_screen_to_shadowmap in vsmshadow_sm_helper2.hlsl(in Book sample of ShaderX5 chapter4.5).

1. 
   
2. //vsmshadow_sm_helper2.hlsl
   
3. 
   
4. float4x4 m4x4_screen_to_shadowmap; // The uniform part of the transformation from screenspace to shadowmapspace
   
5. 
   
6. 
   
7. //-------------------------------------------------------------------------------------------------
   
8. // ScreenspaceToShadowmapspace
   
9. //-------------------------------------------------------------------------------------------------
   
10. 
    
11. inline float4 ScreenspaceToShadowmapspace(float screen_x, float screen_y, float z_view)
    
12. {
    
13.         float4 v4_pos_screen_reprojected = float4( screen_x * z_view, screen_y * z_view, z_view, 1 );
    
14.         float4 v4_pos_lightspace        = mul(v4_pos_screen_reprojected, m4x4_screen_to_shadowmap);
    
15.         return v4_pos_lightspace;
    
16. };
    
17. 
    
18. 
    
19. //-------------------------------------------------------------------------------------------------
    
20. // ScreenspaceToShadowmapCoordinatesAndLightspaceDepth
    
21. //-------------------------------------------------------------------------------------------------
    
22. 
    
23. inline float3 ScreenspaceToShadowmapCoordinatesAndLightspaceDepth(float screen_x, float screen_y, float z_view)
    
24. {
    
25.         float4 pos_light = ScreenspaceToShadowmapspace(screen_x, screen_y, z_view);
    
26. 
    
27.         // Project result into shadowmap coordinates
    
28. 
    
29.         double pos_light_w_inv = 1.0 / pos_light.w;
    
30. 
    
31.         float3 pos_shadowmap =
    
32.                 float3(
    
33.                         0.5 + 0.5 * pos_light_w_inv * pos_light.x, // SM texture x
    
34.                         0.5 - 0.5 * pos_light_w_inv * pos_light.y, // SM texture y
    
35.                         pos_light_w_inv * pos_light.z  // depth in SM space
    
36.                 );
    
37. 
    
38.         return pos_shadowmap;
    
39. };
    

复制代码

1. 
   
2. //vsmshadow_deferred.hlsl
   
3. 
   
4. //-------------------------------------------------------------------------------------------------
   
5. // PsApplySmTileToFramebufferUsingShadowDepthBuffer
   
6. // Apply shadow map tile to the frame buffer using the linear depth values stored in the
   
7. // Shadow Depth Buffer
   
8. //-------------------------------------------------------------------------------------------------
   
9. 
   
10. Ps_DEFAULT_OUT PsApplySmTileToFramebufferUsingShadowDepthBuffer(Ps_TC_IN IN)
    
11. {
    
12.         Ps_DEFAULT_OUT OUT;
    
13.        
    
14.         float shadow_term = 1.0f;
    
15.         const float shadow_ambient = 0.7f;
    
16.         //float shadow_ambient = UNIFORM_shadow_map_ambient;
    
17.        
    
18.         float z_view_center = tex2D(tex_shadow_depth_buffer, IN.v2_tc.xy).w;
    
19. 
    
20.         float3 pos_shadowmap =
    
21.                 ScreenspaceToShadowmapCoordinatesAndLightspaceDepth( IN.v2_tc.x, IN.v2_tc.y, z_view_center );
    
22.         float2 sm_coords = pos_shadowmap.xy;
    
23.         float depth_lightspace = pos_shadowmap.z;
    
24.        
    
25.         // Pixel lies on backplane or query does not concern current tile => Skip Fragment
    
26.         if(
    
27.                 (z_view_center == 0.0f) ||  // skip pixels lying on the backplane (D3D9 only allows DWORDs for Clear, so we have to use 0 here).
    
28.                 (sm_coords.x < 0) || (sm_coords.x > 1) ||  // pixel lies outside of current shdow map tile
    
29.                 (sm_coords.y < 0) || (sm_coords.y > 1)
    
30.         )
    
31.         {
    
32.                 clip(-1);
    
33.         }
    
34. 
    
35.        
    
36. #if(1)
    
37. 
    
38.         shadow_term = (tex2D(tex_shadowmap_tile, sm_coords).x < (depth_lightspace)) ? shadow_ambient : 1.0f;
    
39. 
    
40. #else
    
41. 
    
42.         #include "vsmshadow_adaptive_sm_filtering_inc.hlsl"
    
43. 
    
44. #endif
    
45. 
    
46.         OUT.color = tex2D(tex_shadow_depth_buffer, IN.v2_tc.xy) * shadow_term;
    
47. 
    
48.         return OUT;
    
49. }
    

复制代码