Demystify CGO usage

[sarumaj]

I was wondering if one could replace the CGO binding on some platforms by using ebitengine/purego?

Here an example for clipboard_darwin.go (not tested though, generated with an LLM to give an idea):

package systray

import (
	"time"
	"unsafe"

	"github.com/ebitengine/purego"
	"github.com/ebitengine/purego/objc"
)

var st = &systray{}

type systray struct {
}

// Objective-C selectors
var (
	showMenuSelector          objc.Selector
	setIconSelector           objc.Selector
	setMenuItemIconSelector   objc.Selector
	registerSystraySelector   objc.Selector
	nativeLoopSelector        objc.Selector
	nativeEndSelector         objc.Selector
	nativeStartSelector       objc.Selector
	quitSelector              objc.Selector
	setInternalLoopSelector   objc.Selector
	createMenuSelector        objc.Selector
	setMenuNilSelector        objc.Selector
	resetMenuSelector         objc.Selector
	addOrUpdateMenuItemSelector objc.Selector
)

func init() {
	objc.LoadFramework("Cocoa", "/System/Library/Frameworks/Cocoa.framework")

	showMenuSelector = objc.GetSelector("showMenu")
	setIconSelector = objc.GetSelector("setIcon:withLength:template:")
	setMenuItemIconSelector = objc.GetSelector("setMenuItemIcon:withLength:id:template:")
	registerSystraySelector = objc.GetSelector("registerSystray")
	nativeLoopSelector = objc.GetSelector("nativeLoop")
	nativeEndSelector = objc.GetSelector("nativeEnd")
	nativeStartSelector = objc.GetSelector("nativeStart")
	quitSelector = objc.GetSelector("quit")
	setInternalLoopSelector = objc.GetSelector("setInternalLoop:")
	createMenuSelector = objc.GetSelector("createMenu")
	setMenuNilSelector = objc.GetSelector("setMenuNil")
	resetMenuSelector = objc.GetSelector("resetMenu")
	addOrUpdateMenuItemSelector = objc.GetSelector("addOrUpdateMenuItemWithID:parentID:title:tooltip:shortcut:disabled:checked:checkable:")
}

func (m *systray) ShowMenu() error {
	objc.Call("SystrayManager", showMenuSelector)
	return nil
}

func SetTemplateIcon(templateIconBytes []byte, regularIconBytes []byte) {
	iconPtr := unsafe.Pointer(&templateIconBytes[0])
	objc.Call("SystrayManager", setIconSelector, iconPtr, len(templateIconBytes), true)
}

func (item *MenuItem) SetIcon(iconBytes []byte) {
	iconPtr := unsafe.Pointer(&iconBytes[0])
	objc.Call("SystrayManager", setMenuItemIconSelector, iconPtr, len(iconBytes), item.id, false)
}

func (item *MenuItem) SetTemplateIcon(templateIconBytes []byte, regularIconBytes []byte) {
	iconPtr := unsafe.Pointer(&templateIconBytes[0])
	objc.Call("SystrayManager", setMenuItemIconSelector, iconPtr, len(templateIconBytes), item.id, true)
}

func registerSystray() {
	objc.Call("SystrayManager", registerSystraySelector)
}

func nativeLoop() {
	objc.Call("SystrayManager", nativeLoopSelector)
}

func nativeEnd() {
	objc.Call("SystrayManager", nativeEndSelector)
}

func nativeStart() {
	objc.Call("SystrayManager", nativeStartSelector)
}

func quit() {
	objc.Call("SystrayManager", quitSelector)
}

func setInternalLoop(internal bool) {
	objc.Call("SystrayManager", setInternalLoopSelector, internal)
}

func CreateMenu() {
	objc.Call("SystrayManager", createMenuSelector)
}

func SetMenuNil() {
	objc.Call("SystrayManager", setMenuNilSelector)
}

func SetIcon(iconBytes []byte) {
	iconPtr := unsafe.Pointer(&iconBytes[0])
	objc.Call("SystrayManager", setIconSelector, iconPtr, len(iconBytes), false)
}

func SetTitle(title string) {
	titlePtr := objc.StringToNSString(title)
	objc.Call("SystrayManager", "setTitle:", titlePtr)
}

func SetTooltip(tooltip string) {
	tooltipPtr := objc.StringToNSString(tooltip)
	objc.Call("SystrayManager", "setTooltip:", tooltipPtr)
}

func addOrUpdateMenuItem(item *MenuItem) {
	var disabled, checked, isCheckable int
	if item.disabled {
		disabled = 1
	}
	if item.checked {
		checked = 1
	}
	if item.isCheckable {
		isCheckable = 1
	}
	parentID := 0
	if item.parent != nil {
		parentID = int(item.parent.id)
	}
	objc.Call("SystrayManager", addOrUpdateMenuItemSelector, item.id, parentID, item.title, item.tooltip, item.shortcutKey, disabled, checked, isCheckable)
}

func addSeparator(id uint32) {
	objc.Call("SystrayManager", "addSeparator:", id)
}

func hideMenuItem(item *MenuItem) {
	objc.Call("SystrayManager", "hideMenuItem:", item.id)
}

func showMenuItem(item *MenuItem) {
	objc.Call("SystrayManager", "showMenuItem:", item.id)
}
}

func resetMenu() {
	objc.Call("SystrayManager", resetMenuSelector)
}

func enableOnClick() {
	if !isEnableOnClick {
		isEnableOnClick = true
		objc.Call("SystrayManager", "enableOnClick")
	}
}

func systray_ready() {
	if systrayReady != nil {
		systrayReady()
	}
}

func systray_on_exit() {
	systrayExit()
}

func systray_menu_item_selected(cID int) {
	systrayMenuItemSelected(uint32(cID))
}

func systray_on_click() {
	if dClickTime == 0 {
		dClickTime = time.Now().UnixMilli()
	} else {
		nowMilli := time.Now().UnixMilli()
		if nowMilli-dClickTime < dClickTimeMinInterval {
			dClickTime = dClickTimeMinInterval
			if onDClick != nil {
				onDClick(st)
				return
			}
		} else {
			dClickTime = nowMilli
		}
	}
	if onClick != nil {
		onClick(st)
	}
}

func systray_on_rclick() {
	if onRClick != nil {
		onRClick(st)
	} else {
		objc.Call("SystrayManager", showMenuSelector)
	}
}