Use non-random sequences to initialize ambient occlusion data

This allows selecting the formulas to obtain a better distribution of
values.

diff --git a/source/effects/ambientocclusion.cpp b/source/effects/ambientocclusion.cpp
index b4050aef92428ceeacf44a8924e4a48d07085279..a407c2d9918621b3aa9f057fd93597845635f1e9 100644 (file)
--- a/source/effects/ambientocclusion.cpp
+++ b/source/effects/ambientocclusion.cpp
@@ -41,11 +41,10 @@ const Texture2D &AmbientOcclusion::get_or_create_rotate_lookup()
        rotate_lookup->storage(RGBA8, 4, 4, 1);
        resources.add(name, rotate_lookup);
 
-       unsigned seed = 1;
        unsigned char data[64];
        for(unsigned i=0; i<16; ++i)
        {
-               Geometry::Angle<float> a = Geometry::Angle<float>::from_turns(random(seed));
+               Geometry::Angle<float> a = Geometry::Angle<float>::from_turns(i*7/16.0f);
                unsigned char c = (cos(a)*0.5f+0.5f)*255;
                unsigned char s = (sin(a)*0.5f+0.5f)*255;
                data[i*4  ] = c;
@@ -58,11 +57,12 @@ const Texture2D &AmbientOcclusion::get_or_create_rotate_lookup()
        return *rotate_lookup;
 }
 
-float AmbientOcclusion::random(unsigned &seed)
+float AmbientOcclusion::radical_inverse(unsigned n)
 {
-       static const unsigned modulus = (1U<<31)-1;
-       seed = (static_cast<UInt64>(seed)*48271)%modulus;  // minstd
-       return static_cast<float>(seed)/(modulus-1);
+       unsigned inv = ((n&0x55)<<1) | ((n&0xAA)>>1);
+       inv = ((inv&0x33)<<2) | ((inv&0xCC)>>2);
+       inv = ((inv&0x0F)<<4) | ((inv&0xF0)>>4);
+       return inv/256.0f;
 }
 
 void AmbientOcclusion::set_n_samples(unsigned n)
@@ -70,13 +70,14 @@ void AmbientOcclusion::set_n_samples(unsigned n)
        if(n<1 || n>32)
                throw out_of_range("AmbientOcclusion::set_n_samples");
 
-       unsigned seed = 1;
-       float radius_divisor = (n-1)*(n-1);
        Vector3 sample_points[32];
        for(unsigned i=0; i<n; ++i)
        {
-               Vector3 v(random(seed)-0.5f, random(seed)-0.5f, random(seed)-0.5f);
-               sample_points[i] = normalize(v)*(0.1f+0.9f*i*i/radius_divisor);
+               float z = static_cast<float>(i)/n;
+               float r = sqrt(1.0f-z*z);
+               float d = radical_inverse(i);
+               Geometry::Angle<float> a = Geometry::Angle<float>::from_turns(d);
+               sample_points[i] = Vector3(cos(a)*r, sin(a)*r, z)*(0.1f+0.9f*d*d);
        }
        shdata.uniform3_array("sample_points", n, &sample_points[0].x);
        shdata.uniform("n_samples", static_cast<int>(n));

diff --git a/source/effects/ambientocclusion.h b/source/effects/ambientocclusion.h
index 61d4d4f3e44a48daf94468d684d26f14e4b19ba5..f186db3dcd073a9577d20d44d68c6bd6f9d8185f 100644 (file)
--- a/source/effects/ambientocclusion.h
+++ b/source/effects/ambientocclusion.h
@@ -54,7 +54,7 @@ public:
 
 private:
        static const Texture2D &get_or_create_rotate_lookup();
-       static float random(unsigned &);
+       static float radical_inverse(unsigned);
 
 public:
        void set_n_samples(unsigned);