Cortex RT is a self made CPU based monte carlo path tracer created from scratch in C++.
Cortex supports an extended list of builtin uv mapped primitives mostly for testing purposes :
- Plane
- Cylinder
- Disk
- Cone
- Box
- Torus
- Sphere
| Primitives with test UV texture | Primitives with stone texture |
|---|---|
 |
 |
Cortex RT supports loading Wavefront .obj files.
obj is a kind of old legacy plain text 3D file format but it is still widely used by 3D software (blender, 3ds max, maya...) as an export file format.
- .obj file contains vertex, faces, normals, uv mapping and smmothing groups definition
- .mtl (Material template library) additional file contains materials definition (color, textures, ambient, diffuse, specular, bump...)
If you want to knowm more about obj and mtl files : https://en.wikipedia.org/wiki/Wavefront_.obj_file
| teapot.obj solid color | teapot.obj textured | 3ds max obj exporter |
|---|---|---|
 |
 |
 |
Cortex RT comes with a convenient .scene configuration file system to describe the scene to be rendered (primitives, meshes, camera, lights, materials, textures, rendering quality...)
# teapot_mesh.scene
image:
{
width = 512;
height = 388;
maxDepth = 100;
samplesPerPixel = 100;
background =
{
color = { r = 0.0; g = 0.0; b = 0.0; };
};
};
# Configuration of the camera
camera:
{
aspectRatio = "16:9";
lookFrom = { x = 0.0; y = 4.0; z = 9.0; };
lookAt = { x = 0.0; y = 0.0; z = 0.0; };
upAxis = { x = 0.0; y = 1.0; z = 0.0; };
fov = 18.0;
};
# Lights in the scene
lights:
{
sphereLights: (
{
name = "MySphereLight";
position = { x = 0.0; y = 8.0; z = 5.0; };
radius = 3.0;
intensity = 3.0;
color = { r = 1.0; g = 1.0; b = 1.0; };
invisible = true;
}
)
}
textures:
{
solidColor: (
{
name = "ground_texture";
color = { r = 0.7; g = 0.8; b = 1.0; };
},
),
image: (
{
name = "teapot_diffuse_texture";
filepath = "../../data/models/rusted_metal1.jpg";
}
)
}
materials:
{
lambertian: (
{
name = "ground_material";
texture = "ground_texture";
}
),
phong: (
{
name = "teapot_material";
diffuseTexture = "teapot_diffuse_texture";
ambientColor = { r = 0.0; g = 0.0; b = 0.0; };
shininess = 0.9;
}
)
}
# Meshes in the scene
meshes:
{
obj: (
{
name = "MyTeapotModel"
filepath = "../../data/models/teapot.obj";
position = { x = 0.0; y = 0.0; z = 0.0; };
material = "teapot_material"
use_mtl = false;
use_smoothing = true;
transform =
{
translate = { x = 0.0; y = 0.0; z = 0.0; };
rotate = { x = 0.0; y = 0.0; z = 0.0; };
scale = { x = 0.02; y = 0.02; z = 0.02; };
};
}
);
};
# Primitives in the scene
primitives:
{
# List of boxes
boxes: (
{
name = "MyGround";
position = { x = 0.0; y = -1.0; z = 0.0; };
size = { x = 40.0; y = 0.5; z = 40.0; };
material = "ground_material";
uvmapping = { scale_u = 1.0; scale_v = 1.0; offset_u = 0.0; offset_v = 0.0; repeat_u = 2.0; repeat_v = 2.0; };
}
);
};
Cortex RT mostly support following materials :
- Phong
- Oren Nayar
- Anisotropic (for wood, slate, ice, velvet...)
- Isotropic (for glass, crystals with cubic symmetry, diamonds, plastic, metal...)
- Dielectric (for water, glass, diamond...)
- Lambertian (simple diffuse material without any specular relection)
- Metal (for metals, mirrors...)
- Emissive (WIP)
| crate.obj (diffuse + specular + bump textures) | cushion.obj (diffuse + specular + normal textures) |
|---|---|
 |
 |
 |
 |
The phong reflection model is a full featured material that combines ambient + diffuse + specular. https://en.wikipedia.org/wiki/Phong_reflection_model
On top of that, Cortex RT phong material also support a lot of possible textures (solid color, gradient, image, bump, normal, displacement, alpha...)
# Sample materials section in scene file
materials:
{
lambertian: (
{
name = "ground_material";
texture = "ground_texture";
}
),
phong: (
{
name = "crate_material";
diffuseTexture = "crate_diffuse_texture";
specularTexture = "crate_specular_texture";
#bumpTexture = "crate_bump_texture";
normalTexture = "crate_normal_texture";
ambientColor = { r = 0.0; g = 0.0; b = 0.0; };
shininess = 0.0;
}
)
}
Cortex RT supports quite a lot of textures you can combine in a material :
- Solid color texture
- Gradient color texture
- Image texture
- Bump texture
- Normal texture
- Displacement texture (WIP)
- Alpha texture (transparency texture)
- Perlin texture (procedural noise)
- Checker (procedural checkboard pattern texture)
- Emissive texture (WIP)
# Sample textures section in scene file
textures:
{
image: (
{
name = "ground_texture";
filepath = "../../data/textures/scifi_floor2.png";
},
{
name = "crate_diffuse_texture";
filepath = "../../data/models/crate_diffuse.jpg";
},
{
name = "crate_specular_texture";
filepath = "../../data/models/crate_specular.jpg";
},
{
name = "crate_bump_texture";
filepath = "../../data/models/crate_bump.jpg";
}
),
normal: (
{
name = "crate_normal_texture";
filepath = "../../data/models/crate_normal.jpg";
strength = 0.005;
}
)
}
| Bump texture | Normal texture |
|---|---|
 |
 |
Cortex RT provides 2 kinds of camera : perspective (default) and orthographic (no perception of depth)
| Perspective camera | Orthographic camera |
|---|---|
 |
 |
# Configuration of a perspective camera
camera:
{
aspectRatio = "16:9";
lookFrom = { x = 0.0; y = 2.0; z = 9.0; };
lookAt = { x = 0.0; y = 0.6; z = 0.0; };
upAxis = { x = 0.0; y = 1.0; z = 0.0; };
fov = 18.0; // Field Of View (zoom level in degrees)
};
# Configuration of an orthographic camera
camera:
{
aspectRatio = "16:9";
lookFrom = { x = 0.0; y = 2.0; z = 9.0; };
lookAt = { x = 0.0; y = 0.6; z = 0.0; };
upAxis = { x = 0.0; y = 1.0; z = 0.0; };
orthographic = true;
orthoHeight = 2.0; // Orthographic viewport height (height of the viewport in world space units)
};
The image section in .scene files defines some usefull render settings :
- width/height : The size in pixels of the final rendered image (according to the camera aspect ratio)
- maxDepth : The max number of ray bounces (50 should be more than enough)
- samplesPerPixel (spp) : The max number of samples calculated to generate each pixel of the rendered image (50 is very fast but very noisy, 500-1000 is high quality, 5000+ is extra high quality but very slow)
- background : The background to use while rendering the scene (color, simple image or hdr skybox image)
# Configuration of the rendered image quality
image:
{
width = 512;
height = 388;
maxDepth = 50;
samplesPerPixel = 500;
background =
{
#color = { r = 0.1; g = 0.1; b = 0.1; };
filepath = "../../data/backgrounds/hdr/christmas_photo_studio_02_2k.hdr";
is_skybox = true;
};
};
| 50 spp | 500 spp | 1000 spp | 5000 spp | 10000 spp |
|---|---|---|---|---|
 |
 |
 |
 |
 |
Cortex RT supports 3 different kinds of lights :
-
Omni light : Also known as a point light, an omni light emits light equally in all directions from a single point in space, similar to a light bulb.
-
Directional light : Simulates light coming from a specific direction, as if it were emitted from an infinitely large source, such as the sun.
-
Spot light : More focused light source that emits light in a specific direction within a cone.
Lights are produced by hidden objects (quad or sphere) with an emissive material.
Such objects can be displayed for debug lightning purpose.
| Omni light | Omni light debug (emissive sphere) |
|---|---|
 |
 |
| Directional light | Directional light debug (emissive quad) |
|---|---|
 |
 |
| Spot light | Spot light debug (emissive sphere) |
|---|---|
 |
 |
Cortex RT supports applying transforms to primitives and meshes (translate, rotate, scale). Transform attribute overrides the object position and size already defined.
# Transform applied on a box primitive
primitives:
{
boxes: (
{
name = "MyGround";
position = { x = 0.0; y = -0.28; z = 0.0; };
size = { x = 10.0; y = 0.5; z = 40.0; };
material = "ground_material";
},
{
name = "MyBox"
position = { x = 0.0; y = 0.35; z = 0.0; };
size = { x = 0.7; y = 0.7; z = 0.7; };
material = "uvmapper_material";
uvmapping = { scale_u = 0.5; scale_v = 0.5; offset_u = 0.0; offset_v = 0.0; };
transform =
{
translate = { x = 0.0; y = 0.0; z = 0.0; };
rotate = { x = 0.0; y = 45.0; z = 0.0; };
scale = { x = 2.0; y = 2.0; z = 2.0; };
};
}
);
};
# Transform applied on a custom mesh
meshes:
{
obj: (
{
name = "MyMesh"
filepath = "../../data/models/smooth_sphere.obj";
use_mtl = true;
use_smoothing = true;
transform =
{
translate = { x = -1.3; y = 0.0; z = 0.0; };
rotate = { x = 0.0; y = 45.0; z = 0.0; };
scale = { x = 1.2; y = 1.2; z = 1.2; };
};
}
);
};
In a scene objects (primitives and meshes) can be grouped by using groups. A transform can also be applied to a group.
primitives:
{
boxes: (
{
name = "MyBox1"
position = { x = 0.0; y = 0.0; z = 0.0; };
size = { x = 0.7; y = 0.7; z = 0.7; };
material = "uvmapper_material";
group = "MyGroup";
},
{
name = "MyBox2"
position = { x = 0.0; y = 0.0; z = 0.0; };
size = { x = 0.7; y = 0.7; z = 0.7; };
material = "uvmapper_material";
group = "MyGroup";
}
);
};
# Definition of groups
groups: (
{
name = "MyGroup";
transform =
{
translate = { x = -100.0; y = 270.0; z = 395.0; };
rotate = { x = 0.0; y = 15.0; z = 0.0; };
scale = { x = 2.0; y = 2.0; z = 2.0; };
};
}
);