# Main Loop

# Initialising

The main function in Sandbox only contains 4 lines:

fn main() {
    let mut app = glamour::App::new("Glamour Sandbox", 1920, 1080);
    let sandbox_layer = SandboxLayer::new("SandboxLayer");
    app.push_layer(Box::new(sandbox_layer));
    app.run();
}

Calling glamour::App::new(title: &str, width: u32, height: u32) will do the following:

Create a new event loop from the glutin crate to handle OS I/O
Build a window with the supplied title, width, and height
Load OpenGL within that window's context
Load imgui
Initialise the Layer stack.

After this point, layers can be pushed to the app, and then run.

# Layer

A Layer is a basic trait to handle events of distinct parts of the application. Layers don't communicate with each other through the app, they're meant to be separate. There are only two layers used in the app:

PerfMetricsLayer for reporting performance metrics
SandboxLayer is a place to store all Sandbox related things.

Layer provides a few funtions that an implementation can use:

init()
on_event()
on_fixed_update()
on_frame_update()
on_imgui_update()

Hopfully, those should be fairly self documentating.

# Event Loop

Calling app.run() kickstarts the main event loop, which is responsible for

Polling for events
Managing fixed and frame updates
Updating and rendering imgui
Calling the each layer's Layer trait functions at the appropriate point
Swapping the frame buffer to actual show the rendered image on the screen.

# AppContext

App also maintains a struct that holds the context of the application. This is AppContext, it provides some convenience to access things such as the window context and frame timings. This is passed to each Layer function.

← Architecture Renderer 🚧 →