Bouncy window manager "solution" (screen capture at bottom)

bouncywin.swift

import Cocoa
import Foundation
import AppKit
import CoreFoundation
import ApplicationServices

/// https://jvns.ca/blog/2019/11/25/challenge--make-a-bouncy-window-manager/

/*
 This code runs the following sequence:
 - create a callback for a mouseclick
 - callback figures out the underlying pid for the application of the clicked window
 - callback starts bouncy_window loop which does the actual window movement until
   the program is stopped.
 */

let speed = 1.5

/// place-holder to save the eventTap so we can cancel it inside the callback
var taps: [CFMachPort] = []

func start() {
    let userinfo_ptr: UnsafeMutableRawPointer = UnsafeMutableRawPointer.allocate(byteCount: MemoryLayout.size(ofValue: pid_t()),
                                                                                 alignment: 0)

    /// based on https://stackoverflow.com/a/31898592/508431
    let eventMask = (1 << CGEventType.leftMouseDown.rawValue)
    guard let eventTap = CGEvent.tapCreate(tap: .cgSessionEventTap,
                                          place: .headInsertEventTap,
                                          options: .defaultTap,
                                          eventsOfInterest: CGEventMask(eventMask),
                                          callback: mouseCallback,
                                          userInfo: userinfo_ptr) else {
                                            print("failed to create event tap")
                                            exit(1)
    }
    
    let runLoop = CFRunLoopGetCurrent()
    let runLoopSource = CFMachPortCreateRunLoopSource(kCFAllocatorDefault, eventTap, 0)
    CFRunLoopAddSource(runLoop, runLoopSource, .commonModes)
    CGEvent.tapEnable(tap: eventTap, enable: true)
    // save a reference to the eventTap for cancelation in the callback
    taps.insert(eventTap, at: 0)
}

// callback to get pid from mouse lick
func mouseCallback(proxy: CGEventTapProxy,
                   type: CGEventType,
                   event: CGEvent,
                   refcon: UnsafeMutableRawPointer?) -> Unmanaged<CGEvent>? {

    let nsevent = NSEvent(cgEvent: event)!
    let cgpt = CGPoint(x: nsevent.locationInWindow.x,
                       y: CGDisplayBounds(0).maxY - nsevent.locationInWindow.y)
    
    let axgl = AXUIElementCreateSystemWide()
    let clickel = UnsafeMutablePointer<AXUIElement?>.allocate(capacity: 1)
    AXUIElementCopyElementAtPosition(axgl, Float(cgpt.x), Float(cgpt.y), clickel)

    // set global pid variable
    var pid: pid_t = 0
    AXUIElementGetPid(clickel.pointee!, &pid)
    
    if (taps.count > 0) {
        CGEvent.tapEnable(tap: taps[0], enable: false)
        CFMachPortInvalidate(taps[0])
    }
    
    // run this async so we don't block the callback -- makes the window
    // recording super jittery
    DispatchQueue.global().async {
        bounce_window(pid: pid)
    }

    /// unreachable?
    return Unmanaged.passRetained(event)
}

/// return window size
func getwsize(window: UnsafeMutablePointer<CFTypeRef?>) -> CGSize {
    /// Get window size
    let axsize = UnsafeMutablePointer<CFTypeRef?>.allocate(capacity: 1)
    AXUIElementCopyAttributeValue(window.pointee as! AXUIElement, kAXSizeAttribute as CFString, axsize)
    var wsize = CGSize()
    AXValueGetValue(axsize.pointee as! AXValue, AXValueType(rawValue: kAXValueCGSizeType)!, &wsize)
    return wsize
}

/// set window position
func setpos(window: UnsafeMutablePointer<CFTypeRef?>, _ x: Double, _ y: Double) {
    var p = CGPoint(x: x, y: y);
    let axp: CFTypeRef = AXValueCreate(AXValueType(rawValue: kAXValueCGPointType)!, &p)!;
    AXUIElementSetAttributeValue(window.pointee as! AXUIElement, kAXPositionAttribute as CFString, axp);
}

/// get current window position
func getpos(window: UnsafeMutablePointer<CFTypeRef?>) -> CGPoint {
    var p = CGPoint()
    let axp = UnsafeMutablePointer<CFTypeRef?>.allocate(capacity: 1)
    AXUIElementCopyAttributeValue(window.pointee as! AXUIElement, kAXPositionAttribute as CFString, axp);
    AXValueGetValue(axp.pointee as! AXValue, AXValueType(rawValue: kAXValueCGPointType)!, &p)
    return p
}

/// helpers
func rv() -> Double {
    return Double.random(in: 0..<1)
}
func rvt() -> Double {
    return Double.random(in: 0.5..<(0.9))
}

func nnv(_ v: (Double,Double)) -> (Double,Double) {
    let l = sqrt(pow(v.0,2) + pow(v.1,2))
    return (speed * v.0 / l, speed * v.1 / l)
}

/// check intersection and find next direction
func update(wsize: CGSize, bounds: CGRect, point: CGPoint) -> (Bool, (Double,Double)) {
    let brect = [
        point,
        CGPoint(x: point.x + wsize.width, y: point.y),
        CGPoint(x: point.x, y: point.y + wsize.height),
        CGPoint(x: point.x + wsize.width, y: point.y + wsize.height)
    ]

    var hit: Bool = false
    var dv: (Double, Double) = (0,0)
    
    for checkp in brect {
        if (checkp.x >= bounds.width) {
            dv = (-1.0 * rvt(), rv())
            hit = true
            break
        } else if (checkp.y >= bounds.height) {
            dv = (rv(), -1.0 * rvt())
            hit = true
            break
        } else if (checkp.x <= 1) {
            dv = (1.0 * rvt(), rv())
            hit = true
            break
        } else if (checkp.y <= 26) {
            // 26: need to account for the menu bar
            dv = (rv(), 1.0 * rvt())
            hit = true
            break
        }
    }

    return (hit, nnv(dv))
}

/// get application window PID from a mouse click
/// TODO does not support multiple-window applications

///=======================================================================================================

func bounce_window(pid: pid_t) {
    /// Accessibility API object for application
     let app = AXUIElementCreateApplication(pid)

    /// Get main window from the application
    let w = UnsafeMutablePointer<CFTypeRef?>.allocate(capacity: 0)
    AXUIElementCopyAttributeValue(app, "AXMainWindow" as CFString, w)

    /// Get screen size
    let bounds = CGDisplayBounds(0)
    let wsize = getwsize(window: w)
    var v: (Double,Double) = nnv((rv(), rv()))

    while true {
        let p = getpos(window: w);
        let (hit, nextv) = update(wsize: wsize, bounds: bounds, point: p);
        if hit {
            v = nextv
        }

        setpos(window: w, Double(p.x) + v.0, Double(p.y) + v.1)

        //usleep(3 * 1000);
        DispatchQueue.main.async {
            CFRunLoopRunInMode(CFRunLoopMode.defaultMode, 0.1, true);
        }
    }
}

start()

screencap.gif