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# Computer Graphics Lab2 - Ray Tracing

As explained in `02_RayTracing.html`, your ray _tracer_ reuses the ray _casting_ code that you wrote in the previous assignment. This leaves you with two options.

**Option 1**: You feel confident that your code from lab 1 is correct. In this case, I would recommend that you copy-paste the 6 `.cpp` files from the `src/` folder of the previous assignment into the `lab1/` folder of this repository. In other words, your executable for this lab will also depend on your code from the previous lab.

**Option 2**: You know that your code from lab 2 is functionally incorrect/incomplete. We _could_ give you our solution code, but that would spell all kinds of trouble. So instead we have compiled our solution code into a static library. Thanks to the CMakeLists.txt, CMake will link this library during compilation, and you will be able to call our methods, like `first_hit()` and `viewing_ray()` without viewing our source code. **However, libraries are platform dependent**, and we don't have the patience to compile one for every OS out there. We only support Windows, Ubuntu 20.04, Ubuntu 22.04 (Do you have a newer version and it works? Let us know.) and MacOS with Intel x86_64 chips (and the arm64 chips through Rosetta). More info below.

## Submission

You know the drill. Check if your `rgb.png` files look exactly like those in the `correct_results/` folder.

## Building the project using CMake

Go ahead and have a quick look at `CMakeLists.txt` before you continue. There are 2 main changes. 

1. If you chose Option 1 (use your own files in `lab1/`), then you need to set the `USE_OWN_SRC_FILES_LAB1` parameter on ON (explained below). Then the files in `lab1` will be added to `${SRCFILES}` and passed to the compiler through `add_executable(${PROJECT_NAME} ${SRCFILES})`. Compiling, building and running your code should go without a hitch.
2. If you chose Option 2, then `USE_OWN_SRC_FILES_LAB1` should be OFF. The lines `link_directories(${LIB_PATH})` and `target_link_libraries(${PROJECT_NAME} hw2)` tell the compiler which static library to link. 

Depending on your choice between Option 1 and 2, `USE_OWN_SRC_FILES_LAB1` should be set to `ON` or `OFF` respectively. This can be achieved in several ways, for example:

- by passing a command line arg to cmake, e.g.: `cmake .. -DUSE_OWN_SRC_FILES_LAB1=ON`.
- by overwriting the 5th line in CMakeLists.txt, e.g.: `option(USE_OWN_SRC_FILES_LAB1 "Use the cpp files in lab1/" ON)`

Let's say that you were able to build your executable. When you run it, it will create not only `rgb.png` but also the familiar `depth.png`. If the latter is completely black or looks wrong, then your compiler is not correctly using the code from the previous lab. If you are using Option 2, it means that our static library is incorrect or does not support your platform, so consider switching to Option 1. If that really is not a possibility, contact us.

## Linux, MacOS (and WSL Windows)

Pass `-DCMAKE_BUILD_TYPE=Debug` or `-DCMAKE_BUILD_TYPE=Release` to `cmake` on the command line. So for Option 1:

```
cmake .. -DUSE_OWN_SRC_FILES_LAB1=ON -DCMAKE_BUILD_TYPE=Debug  
```

For Option 2:

```
cmake .. -DCMAKE_BUILD_TYPE=Debug
```

## MacOS new arm64 chips

The static libraries `lib/*/mac/libhw2.a` were compiled with the x86_64 architecture in mind. So in theory, if your Mac can compile the rest of the ray tracing code as x86_64 as well (using Rosetta), you should get a fully working x86_64 executable. This in turn can be run through Rosetta. We don't have a Mac to test this on, so we cannot make it work for you. This worked for one student last year, but there are no guarantees:

```
# download the x86_64 version of cmake
arch -x86_64 /usr/local/bin/brew install cmake  

# run cmake as usual, in the build folder
arch -x86_64 /usr/local/bin/cmake .. -DCMAKE_BUILD_TYPE=Debug

make

# run program
arch -x86_64 ./raytracing ../data/sphere-and-plane.json
```

## Windows

Option 1: you can work in Debug or Release mode, as you wish.

Option 2: you can only work in Release mode, since we did not provide you with `lib/Debug/win/hw2.lib`. So don't forget to change to Release mode in Visual Studio, or your IDE of choice.

Chances are that you don't use CMake on the command line, so just alter line 5 in CMakeLists.txt to your liking.

Note: while building, you might get warnings like `PDB 'hw2.pdb' was not found`, ignore these.