Intro

Here's the motivation behind Telescope: we wanted to use Vulkan for rendering, but couldn't find a good way to create a rendering context using Julia alone. Not even with the (fantastic) SDL2 wrapper (which Starlight still uses for input events).

We also wanted to use the Bullet Physics SDK for physics and especially collision detection, but...no Julia bindings have been created yet.

So we opted to kill two birds with one stone: create our own C++ library to wrap the C/C++ libraries we wanted to use, expose a simple procedural/imperative API through a C header, and create (i.e. generate using Clang.jl) a simple Julia wrapper. Many Yggdrasil pull requests later, Telescope was available as a backend for Starlight.

Starlight's TS subsystem simplifies Telescope's usage by handling initialization, deinitialization, and the frame-by-frame drawing context, but that's really it. Its only job is to make sure that the APIs exposed by the wrapper function as-advertised.

The most important parts of the TS subsystem go something like this:

function awake!(t::TS)
  TS_Init("Hello SDL!", App().wdth, App().hght)
  draw()
  listenFor(t, TICK)
end

function shutdown!(t::TS) 
  unlistenFrom(t, TICK)
  TS_Quit()
end

draw(e) = nothing

function draw()
  TS_VkBeginDrawPass()

  map(draw, scn())

  TS_VkEndDrawPass(vulkan_colors(App().bgrd)...)
end

function handleMessage!(t::TS, m::TICK)
  draw()
end

...where wdth and hght are attributes added to the App struct to specify window dimensions and scn() refers to a special ECSIterator doubling as a new "scene graph" subsystem, which returns entities in reverse-z order (i.e. back to front) for drawing, and functions beginning with TS_ are calls to Telescope's Julia bindings.

Next we'll cover how to create entities in such a way that they get drawn on the screen using Telescope, using an example taken (yet again) from Starlight's own source code.