Some experiments for Cloud lighting

fancy1.cpp

@@ -29,7 +29,7 @@ int main()
     scene.setBackgroundColor(Color(0.529f, 0.808f, 0.922f));
 
     // Add lights
-    auto mainLight = std::make_shared<SunLight>(Vector3d(1.0f, -1.0f, -1.0f), 10.0f);
+    auto mainLight = std::make_shared<SunLight>(Vector3d(-1.0f, -0.5f, -1.0f), 10.0f);
     scene.add(mainLight);
     scene.add(std::make_shared<AmbientLight>(0.3f));
 

shader/cloudshader.cpp

@@ -38,6 +38,7 @@ Color CloudShader::shade(const Scene &scene, const Ray &ray) const
 
     // Step through cloud
     float transmittance = 1.0f;
+    Color cloudColor = Color(1, 1, 1);
     for (int i = 0; i < noiseSamples; ++i)
     {
         // Get sample point
@@ -45,8 +46,10 @@ Color CloudShader::shade(const Scene &scene, const Ray &ray) const
 
         // Get data at point
         float sampleDensity = getCloudDensity(samplePoint) * stepLength;
+//        cloudColor += lightMarch(scene, samplePoint, ray);
 
         transmittance *= exp(-sampleDensity * stepLength * settings.densityAbsorption);
+        if (transmittance <= TRANSMITTANCE_BREAK) break; // No need to continue
     }
 
     // Add some ambient and diffuse lighting
@@ -59,7 +62,7 @@ Color CloudShader::shade(const Scene &scene, const Ray &ray) const
 //        cloud += material.cloud() * illumination.cloud * diffuse;
 //    }
 
-    return background * transmittance + (1.0f - transmittance) * settings.cloudColor;
+    return background * transmittance + (1.0f - transmittance) * cloudColor;
 }
 
 bool CloudShader::isTransparent() const
@@ -84,3 +87,55 @@ float CloudShader::getCloudDensity(Vector3d point) const
 
     return density;
 }
+
+Color CloudShader::lightMarch(const Scene &scene, Vector3d position, const Ray &ray) const
+{
+    Color cloudColor;
+
+    // For alle lights
+    for (const auto &light: scene.lights())
+    {
+        auto illumination = light->illuminate(scene, position);
+
+        // Get light direction
+        Vector3d lightDirection = normalized(illumination.direction);   // Points from surface to light
+
+        // Get length of remaining cloud in light direction
+        float cloudLength = 0.0f;
+
+        Ray cloudRay = ray;
+        cloudRay.origin = position;
+        cloudRay.direction = lightDirection;
+        cloudRay.length = INFINITY;
+        cloudRay.primitive = nullptr;
+
+        // Find other end of cloud
+        if (!ray.primitive->intersect(cloudRay) || cloudRay.length == INFINITY)
+        {
+            // No cloud or at edge
+            continue;
+        }
+        cloudLength = cloudRay.length;
+
+        // Calculate step length
+        int lightSamples = settings.lightSamples;
+        float stepLength = cloudLength / lightSamples;
+
+        // Step through cloud
+        float transmittance = 0.0f;
+        for (int i = 0; i < lightSamples; ++i)
+        {
+            Vector3d samplePoint = position + i * stepLength * lightDirection;
+            float density = getCloudDensity(samplePoint) * stepLength;
+            transmittance *= exp(-density * settings.densityAbsorption);
+
+            if (transmittance <= TRANSMITTANCE_BREAK) break; // No need to continue
+        }
+
+//        float lightAbsorption = dotProduct(lightDirection, ray.direction);  // Approaches 1 when light is parallel to ray
+
+        cloudColor += transmittance * illumination.color;
+    }
+
+    return cloudColor;
+}

shader/cloudshader.h

@@ -3,19 +3,23 @@
 
 #include "scene/scene.h"
 #include "shader.h"
+#include "light/light.h"
 #include "primitive/primitive.h"
 #include "common/noise/worleynoise.h"
 
 int const NOISE_SIZE = 128;
+int const TRANSMITTANCE_BREAK = 0.01f;  // If transmittance goes below this limit, the cloud is considered opaque
 
 struct CloudSettings
 {
     int densitySamples = 100;
+    int lightSamples = 25;
     float scale = 10;
     float densityTreshold = 0.55f;
     float densityIntensity = 2.5f;
     float densityAbsorption = 2;
     Color cloudColor = Color(1, 1, 1);
+    float darknessThreshold = 0.1f;
 };
 
 class CloudShader : public Shader
@@ -35,6 +39,8 @@ private:
     Noise cloudNoise;
 
     float getCloudDensity(Vector3d point) const;
+
+    Color lightMarch(const Scene &scene, Vector3d position, const Ray &ray) const;
 };