Binary files a/doc/output.tga and b/doc/output.tga differ

@@ -25,6 +25,7 @@ using namespace glm;

 /// Constants

 auto const infinity = std::numeric_limits<float>::infinity();

+auto const delta    = 0.001F;

 /// Types

@@ -34,12 +35,20 @@ struct Ray

 {

     vec3 origin;

     vec3 direction;

+    vec3 point(float distance) const

+    {

+        return origin + direction * distance;

+    }

+    Ray resumed(float distance)

+    {

+        return {point(distance), direction};

+    }

 };

 //// Material

 struct Material

 {

-    vec3 color;

+    vec4 color;

 };

 //// Trace

@@ -191,24 +200,34 @@ int main(int argc, char const * argv[])

     };

     auto const scene = Scene{

         // background

-        {vec3(0.2F, 0.2F, 0.5F)},

+        {vec4(0.2F, 0.2F, 0.5F, 0.5F)},

         // shapes

         {

-            {vec3( 2.0F, -1.0F, -10.0F), 3.0F, {vec3(1.0F, 0.0F, 0.0F)}},

-            {vec3( 1.0F,  2.0F,  -7.0F), 2.0F, {vec3(0.0F, 1.0F, 0.0F)}},

-            {vec3(-1.0F,  0.0F,  -4.0F), 1.0F, {vec3(0.0F, 0.0F, 1.0F)}},

-            {vec3( 0.0F, -1.0F,  -3.0F), 0.2F, {vec3(0.0F, 1.0F, 1.0F)}},

+            {vec3( 2.0F, -1.0F, -10.0F), 3.0F, {vec4(1.0F, 0.0F, 0.0F, 1.0F)}},

+            {vec3( 1.0F,  2.0F,  -7.0F), 2.0F, {vec4(0.0F, 1.0F, 0.0F, 1.0F)}},

+            {vec3(-1.0F,  0.0F,  -4.0F), 1.0F, {vec4(0.0F, 0.0F, 1.0F, 1.0F)}},

+            {vec3( 0.0F, -1.0F,  -3.0F), 0.2F, {vec4(0.0F, 1.0F, 1.0F, 0.5F)}},

         },

     };

     auto const tonemap = ACES{vec3(1.0F)};

     auto const output  = TGA{uvec2(640, 480), path};

     //// Render

     output.render([&](uvec2 const & size, uvec2 const & pixel) {

-        auto const ray   = camera.ray(size, pixel);

-        auto const trace = scene.trace(ray);

-        auto const rgb   = trace.material.color;

-        auto const srgb  = convertLinearToSRGB(tonemap.transform(rgb));

-        auto const alpha = 1.0F;

+        auto rgb   = vec3(0.0F); // Pre-multiplied alpha (opacity).

+        auto trans = 1.0F;       // 1 - alpha (opacity).

+        auto ray   = camera.ray(size, pixel);

+        while (true)

+        {

+            auto trace = scene.trace(ray);

+            auto color = trace.material.color;

+            rgb   += color.rgb() * color.a * trans;

+            trans *= 1.0F - color.a;

+            if (trace.distance == infinity || trans == 0.0F)

+                break;

+            ray = ray.resumed(trace.distance + delta);

+        }

+        auto const alpha = 1.0F - trans;

+        auto const srgb  = convertLinearToSRGB(tonemap.transform(rgb / alpha));

         return vec4(srgb, alpha);

     });

 }