Simple Ray tracing framework Sim Rt is based on the mini-book series of Peter Shirley that can be found on his github. It's a hobby project to learn about the basics of CPU Ray tracing and modern C++17.
| Cornell Box | Material test | Environment map |
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| Meshs and instancing | Texture test | Debug rays |
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This sections covers algorithms and techniques that might be implemented in the future.
- Scene format for describing scenes and materials
- Photon mapping for faster calculation of global illumination
- Importance sampling for faster convergence rates
- Improved OBJ loader
The main application can be used as a command line tool. It can be called with
.\sim-rt.exe <SCENE_PATH> <OUTPUT_IMAGE_PATH>?
while the path of the output image path is optional. If it's not specified it defaults to:
.\sim-rt.exe <SCENE_PATH> .\unnamed.png
The file consists of 5 parts namely TRACER, CAMERA, MATERIALS, OBJECTS and SCENE. The parts should be specified in the file in this order to avoid unexpected errors as the scene is constructed on the fly and might depend on previously defined parts. In the following all 5 parts are described in detail.
Specifies the type of tracer, the image resolution of the image plane and thus the resolution of the output image, the number of samples per pixel and the trace depth per ray.
TRACER
TYPE raytracer
RESOLUTION 1080 720
SAMPLES 100
DEPTH 100
So far there are three different types of tracers raycaster, raytracer and debugtracer. The debugtracer renders the intersections between the rays and the scene and displays those intersections as spheres, while rendering the scene from a different angle than the camera and tries to be far away enough such that the whole scene is visible.
The resolution keyword has to be followed by two positive integer numbers bigger than zero. The first number is the width of the output image and the second number is the height of the output image.
The number of samples has to be followed by one positive integer number bigger than zero. The number of samples specifies the number of rays emitted per pixel. The resulting colors per ray are averaged to get the final pixel color.
The depth keyword is followed by a positive integer number bigger than zero. It specifies the trace depth i.e. the number of indirections.
Specifies the camera type and coordinate system. The camera together with the image plane specify the visible scene.
CAMERA
TYPE simple
POS (0,0,-2)
LOOKAT (0,0,0)
UP (0,1,0)
FOV 45.0
There are two camera types, simple which models a pinhole camera and dof which models a camera with a specified focal length.
The position of the camera is specified by a 3D vector. Together with the look at position it specifies the direction the camera is looking at. The up vector is needed to specify the orientation of the camera. The up vector mustn't be parallel to the view direction of the camera.
The field of view is followed by a positive floating point value beteen (0, 180) while 0 and 180 are not valid values.
CAMERA
TYPE dof
...
APERTURE 2.0
The dof camera has an additional attribute for the size of the aperture. Bigger values result in blurrier images while an aperture of 0 is completely sharp. It is important to note that the look at point is also the focus point of the dof camera.
Materials describe the behavior of the rays when intersection with an object. In general there are three possible kinds of interactions, namely absorption, reflection and refraction.
MATERIALS
MATERIAL
NAME normalcolor
TYPE normal
MATERIAL
NAME red
TYPE lambertian
COLOR (1,0,0)
MATERIAL
NAME profilephoto
TYPE lambertian
PATH ../image/sample1.jpg
MATERIAL
NAME metal
TYPE metal
COLOR (0.3,0.4,0.2)
The list of materials starts with the MATERIALS keyword. Then each material has to start with the MATERIAL keyword and then a list of attributes.
The name and the type attribute are required for all materials. The name is used to identify the material thus it has to be unique among all materials. This name is used in the MATERIAL attribute of the objects that follow after the list of materials. The type attribute specifies what kind of material will be used.
The supported types are normal, lambertian, metal, dielectric, diffuselight, brdf and isotropic.
COLOR (0.3,0.2,0)
Furthermore has the texture to be specified. As described in the Peter Shirleys book Raytracing in one weekend, a simple color is also seen as a texture of constant color. Therefore there are three different types of textures supported. The constant texture is specified by the COLOR keyword followed by a vector describing a RGB triplet. The values range from 0 to 1, where (0,0,0) is black and (1,1,1) is white.
PATH ../image/sample1.jpg
The second option is a normal 2D texture which is specified by the PATH keyword followed by an absolute or relative path to an image file. The root for the relative path is the directory where the scene file resides.
CUBEMAP
PATH ../image/cubemap/posx.png
PATH ../image/cubemap/negx.png
PATH ../image/cubemap/posy.png
PATH ../image/cubemap/negy.png
PATH ../image/cubemap/posz.png
PATH ../image/cubemap/negz.png
The third option is a cubemap consisting of six images for all six sides of a cube. It is specified with the CUBEMAP keyword followed by six PATH statements with either absolute or relative paths. The orientation in which the six images are specified is important. By imagining an axis alligned cube, while looking along the negative z-axis, the six sides of the cube map are positive x, negative x, positive y, negative y, positive z and negative z or alternatively right, left, top, bottom, front and back.
Exactly one of the three texture types should be specified. If nothing is specified then a constant white texture is used as a fallback. If more than one of those keywords is specified then the order of preference is PATH > CUBEMAP > COLOR, where PATH has the highest priority.
PATH ../image/sample1.jpg
ITPLT bilinear
WRAP clamp repeat
For the textures one can also specify two texture attributes. The first attribute is the interpolation method specified by the keyword ITPLT followed by either bilinear or nearest. Where bilinear performs a bilinear interpolation and nearest picks the color or the closest pixel. The other attribute is the wrap behaviour when the texture coordinates of the object are greater than 1.0 or smaller than 0.0. This attribute is specified by the WRAP followed by one or two values. Those values can be clamp or repeat, while the first values describes the behaviour in u-direction und the second one v-direction. If only one value is specified then this values is used for both u- and v-direction. Clamping uses the value at the border of the texture while repeat repeats the texture in this direction.
In the following the different material types are specified in order.
MATERIAL
NAME foo
TYPE normal
The normal material is the simplest material as it only has a name and a type attribute. The normal material is mostly for debugging purposes as it color codes the orientation of the normal with rgb(n) = (n+1)/2, assuming that the normal n is normalized.
MATERIAL
NAME foo
TYPE lambertian
COLOR (0.2,0.8,0.4)
PATH ../image/profile1.jpg
CUBEMAP
PATH ../image/cubemap/posx.png
PATH ../image/cubemap/negx.png
PATH ../image/cubemap/posy.png
PATH ../image/cubemap/negy.png
PATH ../image/cubemap/posz.png
PATH ../image/cubemap/negz.png
Lambertian material describes perfectly diffuse material, so material that has no specular terms like reflection and refraction. For the lambertian material the texture has to be specified using either color, image path or cube map image paths.
MATERIAL
NAME foo
TYPE metal
COLOR (0.2,0.8,0.4)
PATH ../image/profile1.jpg
CUBEMAP
PATH ../image/cubemap/posx.png
PATH ../image/cubemap/negx.png
PATH ../image/cubemap/posy.png
PATH ../image/cubemap/negy.png
PATH ../image/cubemap/posz.png
PATH ../image/cubemap/negz.png
Metal acts as a perfect mirror and has no diffuse or refractive terms. The color of the ray is tinted with the color of the texture. For the metal the texture has to be specified using either color, image path or cube map image paths.
MATERIAL
NAME foo
TYPE dielectric
COLOR (0.2,0.8,0.4)
PATH ../image/profile1.jpg
CUBEMAP
PATH ../image/cubemap/posx.png
PATH ../image/cubemap/negx.png
PATH ../image/cubemap/posy.png
PATH ../image/cubemap/negy.png
PATH ../image/cubemap/posz.png
PATH ../image/cubemap/negz.png
COEFF 1.52
Dielectrics or non-metals are a mix of relflective and refractive terms. The probability of refraction and reflection depends on the angle of incident. If a ray hits the surface perpendicular the probability for refraction is highest while a near parallel ray has the highest probability of reflection.
In addition the refractive index has to be specified with the COEFF keyword followed by a floating point number. Typical values are given in the table below:
| type | refractive index |
|---|---|
| air | 1.0 |
| water | 1.333 |
| ice | 1.31 |
| glass | 1.52 |
| diamond | 2.42 |
MATERIAL
NAME foo
TYPE diffuselight
COLOR (0.2,0.8,0.4)
PATH ../image/profile1.jpg
CUBEMAP
PATH ../image/cubemap/posx.png
PATH ../image/cubemap/negx.png
PATH ../image/cubemap/posy.png
PATH ../image/cubemap/negy.png
PATH ../image/cubemap/posz.png
PATH ../image/cubemap/negz.png
Diffuse light is used for light sources where the object emits light uniformly in all directions. When a raytracer is used, at least on object has to have diffuse light material, else the whole scene will be black. The texture attribute describes the color of the light.
MATERIAL
NAME foo
TYPE brdf
COLOR (0.2,0.8,0.4)
PATH ../image/profile1.jpg
CUBEMAP
PATH ../image/cubemap/posx.png
PATH ../image/cubemap/negx.png
PATH ../image/cubemap/posy.png
PATH ../image/cubemap/negy.png
PATH ../image/cubemap/posz.png
PATH ../image/cubemap/negz.png
METALNESS 1.0
ROUGHNESS 0.3
KD 0.2
This material uses the Cook-Torrance BRDF for physically based shading. It consists of a diffuse and a specular part. The metallness factor specifies if the material is a metal 1.0 or a dielectric 0.0. The model also allows for metallness factors in between 0.0 and 1.0. The roughness factor specifies how much the rays will be scattered. For a factor of 1.0, the light is scattered in all directions and it results in a flat color. For numbers near 0.0 the material has small bright highlights. The highlights get bigger and darker with increasing roughness. The factor KD specfies the probability of diffuseness. For a value of 1.0 the material is completely diffuse, while a value of 0.0 is completely specular and acts as a metal.
MATERIAL
NAME foo
TYPE isotropic
COLOR (0.2,0.8,0.4)
PATH ../image/profile1.jpg
CUBEMAP
PATH ../image/cubemap/posx.png
PATH ../image/cubemap/negx.png
PATH ../image/cubemap/posy.png
PATH ../image/cubemap/negy.png
PATH ../image/cubemap/posz.png
PATH ../image/cubemap/negz.png
Isotropic material should be used with volumes. It describes volumes that scatter rays uniformly in all directions. The texture specifies the color of the volume.
The objects list specifies the geometry used. There are several object types that are going to be elaborated together with their attributes.
OBJECTS
OBJECT
NAME light
TYPE sphere
POS (0,2,2)
R 1.0
MATERIAL light
OBJECT
NAME environment
TYPE cube
POS (0,0,0)
WIDTH 10
HEIGHT 10
DEPTH 10
INVERT true
MATERIAL environment
OBJECT
NAME cat1
TYPE mesh
PATH ../mesh/cat.obj
INVERT false
NORMALIZE true
SMOOTH true
MATERIAL gold
Supported object types are cube, cylinder, rectangle, sphere and mesh.
OBJECT
NAME foo
TYPE cube
POS (0,0,0)
WIDTH 10
HEIGHT 10
DEPTH 10
INVERT true
MATERIAL environment
A cube is specified by its position, and the dimensions width, height and depth. In addition there is a bool variable that flips the normals of the cube sides inwards if set to true. If not specified this attribute is false.
OBJECT
NAME foo
TYPE cylinder
POS (0,0,0)
POS2 (0,1,1)
R 2.0
MATERIAL glass
Cylinders have a start and end position as well as the radius of the cylinder.
OBJECT
NAME foo
TYPE rectangle
POS (0,0,0)
XAXIS (2,0,0)
YAXIS (0,3,0)
MATERIAL metal
A rectangle is specified by the position which is the position of the origin, and two axes that specify the plane and the half lenghts of the rectangle. The normal is calculate by n = (xaxis x yaxis) / ||xaxis x yaxis||.
OBJECT
NAME foo
TYPE sphere
POS (0,0,0)
R 2.0
MATERIAL red
A sphere has a position and a radius.
OBJECT
NAME foo
TYPE mesh
PATH ../mesh/cat.obj
INVERT false
NORMALIZE true
SMOOTH true
MATERIAL gold
Mesh is the most interesting object type since it allows to load obj files from the specified path. In addition three mesh attributes can be set. The normalize attribute flips the normals if set to true, its set to false when not specified. The normalize attribute scales down the mesh to fit inside a sphere with radius 1 when set to true. Its also set to false when not specified. The smooth attribute averages vertex normals at the edges where multiple triangle connect. It is also set to false when not specified.
The scene puts everything together. Only objects that are specified in the scene will be visible. So objects that had been specified in the objects list but not in the scene won't be visible in the scene. Objects in the scene can be transformed to allow for instancing.
SCENE
TYPE bvh
ELEMENTS
ELEMENT
OBJECT light
ELEMENT
OBJECT environment
ELEMENT
OBJECT cat1
TRANSFORM
ROTATE (0,1,0) 10
TRANSLATE (0.5,0,-1)
The scene starts with a SCENE keyword and followed by the type of the scene's organization which can be either bvh for a bounding volume hierarchy or list for a simple list.
Then the list of scene elements is specified by the ELEMENTS keyword followed by a list of elements. An element has to have a object attribute with the name of the attribute that has been specified in the objects list before.
In addition to that there is a transform attribute that transforms the respective object. The TRANSFORM keyword is followed by a list of transformations. One kind of transformation is a rotation which is specified by the axis of rotation and a counter-clockwise rotation angle in degrees. The other kind of transformation is a translation which is specified by a 3D vector which describes the direction of the translation. Those transformations can be mixed and there can be many tranformation types while the transformations are executed from top to down.
The mesh cat.obj was made by Juno Huang and is provided under the Royalty Free Licence.
The MIT License (MIT)
Copyright (c) 2019 Adrian Derstroff
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
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