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source: code/branches/skybox/Media/materials/programs/varianceshadowreceiverfp.cg @ 883

Last change on this file since 883 was 390, checked in by landauf, 17 years ago

added materials

File size: 4.1 KB
Line 
1/////////////////////////////////////////////////////////////////////////////////
2//
3// shadowreceiverfp.cg
4//
5// Hamilton Chong
6// (c) 2006
7//
8// This is an example fragment shader for shadow receiver objects. 
9//
10/////////////////////////////////////////////////////////////////////////////////
11
12
13sampler2D ShadowMap : TEXUNIT0;
14
15// Define outputs from vertex shader.
16struct Vertex
17{
18  float4 position       : POSITION;     // fragment position in post projective space
19  float4 shadowCoord    : TEXCOORD0;    // fragment position in shadow map coordinates
20  float  diffuse        : TEXCOORD1;    // diffuse shading value
21};
22
23struct Fragment
24{
25    float4 color  : COLOR0;
26};
27
28Fragment main(Vertex        In,
29              uniform float uSTexWidth,
30              uniform float uSTexHeight)
31{
32    Fragment Out;
33
34    // compute the shadow coordinates for texture lookup
35    // NOTE: texture_viewproj_matrix maps z into [0,1] range, not [-1,1], so
36    //  have to make sure shadow caster stores depth values with same convention.
37    float4 scoord = In.shadowCoord / In.shadowCoord.w;
38
39
40    // -- Bilinear Filtering of Sample --------------------------------------------
41
42    // One could use scoord.xy to look up the shadow map for depth testing, but
43    // we'll be implementing a simple "percentage closest filtering" algorithm instead.
44    // This mimics the behavior of turning on bilinear filtering on NVIDIA hardware
45    // when also performing shadow comparisons.  This causes bilinear filtering of
46    // depth tests.  Note that this is NOT the same as bilinear filtering the depth
47    // values and then doing the depth comparison.  The two operations are not
48    // commutative.  PCF is explicitly about filtering the test values since
49    // testing filtered z values is often meaningless. 
50
51    // Real percentage closest filtering should sample from the entire footprint
52    // on the shadow map, not just seek the closest four sample points.  Such
53    // an improvement is for future work.
54
55   
56    // NOTE: Assuming OpenGL convention for texture lookups with integers in centers.
57    //  DX convention is to have integers mark sample corners
58    float2 tcoord;
59    tcoord.x = (scoord.x * uSTexWidth) - 0.5;
60    tcoord.y = (scoord.y * uSTexHeight) - 0.5;
61    float x0 = floor(tcoord.x);
62    float x1 = ceil(tcoord.x);
63    float fracx = frac(tcoord.x);
64    float y0 = floor(tcoord.y);
65    float y1 = ceil(tcoord.y);
66    float fracy = frac(tcoord.y);
67   
68    // sample coordinates in [0,1]^2 domain
69    float2 t00, t01, t10, t11;
70    float invWidth  = 1.0 / uSTexWidth;
71    float invHeight = 1.0 / uSTexHeight;
72    t00 = float2((x0+0.5) * invWidth, (y0+0.5) * invHeight);
73    t10 = float2((x1+0.5) * invWidth, (y0+0.5) * invHeight);
74    t01 = float2((x0+0.5) * invWidth, (y1+0.5) * invHeight);
75    t11 = float2((x1+0.5) * invWidth, (y1+0.5) * invHeight);
76   
77    // grab the samples
78    float2 z00 = tex2D(ShadowMap, t00).xy;
79    float2 z01 = tex2D(ShadowMap, t01).xy;
80    float2 z10 = tex2D(ShadowMap, t10).xy;
81    float2 z11 = tex2D(ShadowMap, t11).xy;
82
83    // bilinear filter the sample data
84    float2 d0 = ((1.0 - fracx) * z00) + (fracx * z10);
85    float2 d1 = ((1.0 - fracx) * z01) + (fracx * z11);
86    float2 datum = ((1.0 - fracy) * d0) + (fracy * d1);
87
88    // -- Variance Shadow Mapping ---------------------------------------------------
89
90    float zVariance = datum.y - (datum.x * datum.x);
91    float zDeviation = scoord.z - datum.x;
92    zDeviation = (zDeviation < 0.0) ? 0.0 : zDeviation;
93    float visibility = zVariance / (zVariance + (zDeviation * zDeviation));
94    float ztest = (scoord.z < datum.x) ? 1.0:0.0;  // filtering depth ok, because used only for small variance
95    visibility = (zVariance > 0.0) ? visibility : ztest; // if variance too small, we get garbage
96    //0.0000001
97
98    // determine that all geometry within pixel border of shadow map (and outside) is lit
99    float filterBorder = max(invWidth, invHeight);
100    visibility = (all(abs(scoord.xy-0.5)<=0.5-filterBorder)) ? visibility : 1.0;
101
102    // ------------------------------------------------------------------------------
103
104    visibility *= In.diffuse;
105    Out.color = float4(visibility, visibility, visibility, 0.0);
106    return Out;
107}
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