Lab 2 - File Specification

Scene Description

Your raytracer should understand the following xml based format. Please make sure that everything is supported, otherwise we cannot grade your solution.

The input file begins with the header and a scene node, that specifies the output file, followed by the camera specifications. This is followed by the lights and surfaces. Each surface consists of a material, and zero or more transformations. Note that the transformations should be composed in the order they appear in the file.

Basic

Every file has to start with this header that specifies the xml version and the schema that should be used:

The scene node is the main node in the scene file. Every other node has to be a child node of it. The output is sends to the file specified by output_file, in this example to "myImage.png".
background_color sets the color of the background for when rays do not intersect any geometry.

Everything in the file between <!-- and --> should be treated as a comment (as always in XML).

Camera

The camera node has to appear once in every file in the scene node. It has to include the following information:

<position x="1.0" y="-2.0E-10" z="-3"/>

Location of the camera in world coordinates.

<lookat x="1" y="2" z="3"/>

The camera is looking at this point in space.

<up x="1" y="2" z="3"/>

The vector defines which direction is up.

<horizontal_fov angle="45"/>

The angle, in degrees, specifies half of the angle from the left side of the screen to the right side of the screen. When you're rendering your image, you'll use this number to space out the rays you fire. You should scale this angle appropriately in the Y direction based on the resolution of the output image. If the image is wider than tall, the angle from top to bottom will be proportionately smaller.

<resolution horizontal="1920" vertical="1080"/>

The pixel resolution of the final output image.

<max_bounces n="100"/>

n is the maximum number of bounces for reflection and refraction.

Light

All the lights in the scene should be grouped in the lights node. There are four different light types that can be used in the scene:

Defines an ambient light with color (r,g,b) - all objects are illuminated by this light. Note: the world can have precisely one ambient light.

Defines a parallel light with color (r,g,b) - much like the sun, these lights are infinitely far away, and only have a direction vector direction (x,y,z).

Defines a point light with color (r,g,b) and position (x,y,z).

Defines a spot light - this is optional for your assignment. Spot lights exist at a point in space (position) and point in a given direction. falloff with angle1 and angle2, both in degrees, specify how the light falls off. For any angle between zero and angle1, the light should be just like a point light. Between angle1 and angle2, the light falls off. For angles greater than angle2, the light isn't there. If you do this, start with linear falloff, then you may want to play with various gamma functions.

Surface/Geometry

All surfaces of these scene have to be grouped in the surface node. There are two different types of geometric primitives:

This adds a sphere to the world centered at the given point (position) with the given radius.

Adds a triangle mesh specified using the OBJ file format. Please note, that you should not write a complete OBJ parser! However, your parser should be able to read in vertices, normals, and texture information.

Material

This defines a non-textured material

<color r="0.1" g="0.2" b="0.3"/>

Specifies the materials color.

<phong ka="1" kd="1" ks="1" exponent="1"/>

Specifies the coefficients for the phong illumination model. ka is the ambient component, kd is the diffuse component ks is the specular component and exponent is the Phong cosine power for highlights.

<reflectance r="1.0"/>
<transmittance t="1.0"/>

Specifies the reflactance r (fraction of the contribution of the reflected ray) and the transmittance t (fraction of contribution of the transmitting ray). Note: For Fresnel reflection reflactance and transmittance are not needed

<refraction iof="1"/>

Specifies the index of refraction iof

Usually, 0 <= Ka <= 1, 0 <= Kd <= 1, and 0 <= Ks <= 1, though it is not required that Ka + Kd + Ks == 1. Note that transmitting objects (T > 0) are considered to have two sides for algorithms that need these (normally objects have one side). Please note, that you should be able to handle total internal reflection properly.

This defines a textured material

<texture name=""/>

Specifies the texture file that should be used for this material.

All other inputs are the same as the non-textured material.

Transformation

Transformations can be specified in every geometric primitive (sphere/mesh). There can be zero or more transformations that should be applied in the order of their appearence in the block.

<translate x="1" y="1" z="1"/>

Moves an object by the vector [x,y,z].

<scale x="1" y="1" z="1"/>

Scales an object by x on the x-axis, y on the y-axis and z on the z-axis.

<rotateX theta="1"/>
<rotateY theta="1"/>
<rotateZ theta="1"/>

Rotates an object by theta degrees around the specific axis.

Example

The following is an example of the type of input you should expect:

---

Last modified: February 03, 2017

Lukas Herzberger / a1006039 AT unet DOT univie DOT ac DOT at