cacao/appkit/src/view/class.rs

//! This module does one specific thing: register a custom `NSView` class that's... brought to the
//! modern era.
//!
//! I kid, I kid.
//!
//! It just enforces that coordinates are judged from the top-left, which is what most people look
//! for in the modern era. It also implements a few helpers for things like setting a background
//! color, and enforcing layer backing by default.

use std::sync::Once;

use cocoa::base::{id, nil, YES};

use objc::declare::ClassDecl;
use objc::runtime::{Class, Object, Sel, BOOL};
use objc::{class, msg_send, sel, sel_impl};

/// Enforces normalcy, or: a needlessly cruel method in terms of the name. You get the idea though.
extern fn enforce_normalcy(_: &Object, _: Sel) -> BOOL {
    return YES;
}

extern fn update_layer(this: &Object, _: Sel) {
    unsafe {
        let background_color: id = msg_send![class!(NSColor), redColor];
        if background_color != nil {
            let layer: id = msg_send![this, layer];
            let cg: id = msg_send![background_color, CGColor];
            let _: () = msg_send![layer, setBackgroundColor:cg];
        }
    }
}

/// Injects an `NSView` subclass, with some callback and pointer ivars for what we
/// need to do.
pub(crate) fn register_view_class() -> *const Class {
    static mut VIEW_CLASS: *const Class = 0 as *const Class;
    static INIT: Once = Once::new();

    INIT.call_once(|| unsafe {
        let superclass = Class::get("NSView").unwrap();
        let mut decl = ClassDecl::new("RSTView", superclass).unwrap();

        decl.add_method(sel!(isFlipped), enforce_normalcy as extern fn(&Object, _) -> BOOL);
        decl.add_method(sel!(requiresConstraintBasedLayout), enforce_normalcy as extern fn(&Object, _) -> BOOL);
        decl.add_method(sel!(wantsUpdateLayer), enforce_normalcy as extern fn(&Object, _) -> BOOL);
        decl.add_method(sel!(updateLayer), update_layer as extern fn(&Object, _));
        
        VIEW_CLASS = decl.register();
    });

    unsafe {
        VIEW_CLASS
    }
}