---
title: BlackPink (Manifold Raymarching Rendering Engine)
author: _"A Blazing 100x100px at 10FPS"_
...


(we had to name it that because Joel likes naming things after pop artists.)

---

# Objective

Can we use raymarching to render primitive objects inside an arbitrary manifold
in real time?

"Non-euclidean rendering" in the most generalised form possible.

---

# Raymarching

- an approximate and fast form of 'raytracing'
- good for primitives (spheres, boxes et cetera.)
- still very expensive

---

# Manifolds

Only one of us does galaxy brain maths.

---

# Tech Stack Requirements

- Fast, compiled code
- We are relatively familiar with it (that disqualifies any _modern_ or "good"
    language, and C++)
- Need n-dimensional vectors
- Need to draw pixels on a window
- not Java

---

# C and libSDL2

Its fast (to run) and we "know" it. C is a nice language if only for the 
simplicity of its mental model. 

libSDL2 is what the big kids like Valve use.

- nicely handles threading, drawing, timers, and gets out of the way. 

---

Richal spent 10 hours writing a vector library from scratch.

N-dimentional determinants and cross products _sound_ simple. 

---

At one point we were leaking memory at approximately 150Mb per second.

![lots of vagrind errors](img/b1.jpg)

---

![1pm Saturday](img/b3.png)

---

![Fail states were often interesting](img/b2.png)

---

12 Hours later, we could render 

- circles
- boxes, and 
- straight lines 

from one angle, and move them around the scene 

- as long as we got lucky with whatever the 4th dimension was doing. 

Plus some post-processing and lighting.

---

![a green sphere](img/b4.jpg)

---

# Results

A 3D renderer where all the maths is done in n-dimensions. 

> video

---

# Takeaways 1

- sticking raymarching vectors to manifolds in 4 dimensions is possible but has 
    a lot of edge cases 

---

# Takeaways 2 

- having RAII would be really nice when writing a vector library 

```c
    if (1 || keyboardstate[SDL_SCANCODE_UP]) {
        struct ray cameraray = {.pos = copy_vec(camera->pos), .dir = camera->y};
        manifoldturn(&cameraray, camera->x, 0);
        free_vec(cameraray.pos);

        cameraray.pos = copy_vec(camera->pos);
        manifoldturn(&cameraray, camera->y, 0);
        free_vec(cameraray.pos);

        cameraray.pos = camera->pos;
        manifoldstep(&cameraray, dist);
        free_vec(cameraray.pos);
    }
```