There are two ways to render a 3d scene into a 2d image: `rasterization`, which converts the shapes and geometric figures to pixels and applies calculations to obtain the color, the shadows, the refraction, etc... of those pixels. The other method is called `ray tracing` and consists in drawing each pixel with its color, shadows, refraction, reflection, etc.... already present from the start.
Imagine a camera pointing at a scene, and from that camera, a bunch of rays are coming, which bounce from object to object until they reach the light source (lamp, sun, etc...). This is basically how a ray tracer works.
In `ray tracing` each of these rays can be seen as a pixel in the image captured by the camera. Recursively the ray tracer will calculate where the light comes from in that pixel, allowing to give that pixel a color with some shadow aspect, some refraction aspect, and so on.
As your ray tracer will probably be a bit slow to render high resolution scenes, you should make 4 .ppm images for the auditors to evaluate. The scenarios of these 4 images that you have to create consist of:
All the images should be in the format of 800x600. However, while testing, you should use smaller resolution images in order to reduce your rendering time (a 1200x1000 can take up to 40 mins to create). It would be best to consider the possibility of changing the output image's resolution easily.
Another aspect you should consider is that the auditor will have to use your ray tracer, so make it as usable and optimized as possible. You should provide the auditor clear documentation.
By documentation, we mean the explaining of how the ray tracer work and how to work with it, for example: how to create an object, how to change brightness in a scene, etc... After reading the documentation, a new user of your ray tracer has to be able to use it without much guessing work.
In order to render images you will create a [.ppm](https://www.cs.swarthmore.edu/~soni/cs35/f13/Labs/extras/01/ppm_info.html) file. A .ppm file consists of an image header and an image body. Example:
- the first one is the image format: what type of PPM (full color, ASCII encoding) image it is. P3 stands for the Portable PixMap type, so you will be using this one.
- the following stands for how many columns and rows of pixels the image will contain.
- and the third line is the maximum color value, 255 is the most common value since the rgb color code is very well known.
All the other lines below, are the rgb values for each pixel, for example the first line of the image body represents a black pixel (rgb(0,0,0) -> black). Each line represents one pixel, starting on the top left corner transitioning to the right and, in this case, the fifth line is the pixel in the first row on the second column.
So with this in mind, you will have to make an algorithm that fills a file by printing each line. You can use the cargo command this way: `cargo run > output.ppm`. This will print the standard output to the file `output.ppm`.
Consider putting your bonuses behind command-line flags to achieve a reasonable performance standard defined above. For example, to render textures on your image, you can use a flag -t. Otherwise, textures will be ignored.
