First working version

Seems to be working fine - need a better way to decouple ui.py from main logic in main.py - callback layout feels messy
Also want to add a checkbox in future to automatically clip to any fullscreen application
As usual, use at your own risk - I made this for personal use for games that haven't been set up properly to prevent cursor drift on multi-monitor setups or when running in a window

cursor.py

@@ -0,0 +1,47 @@
+#!/usr/bin/env python
+# coding: utf-8
+
+import winfunctions as wf
+
+
+class Clip:
+    def __init__(self, bounds):
+        self._bounds = bounds
+        self._old_bounds = None
+
+    def __del__(self):
+        try:
+            if self.clipped:
+                self.release()
+        except AttributeError:
+            pass
+
+    @staticmethod
+    def clearClips():
+        wf.ClipCursor(None)
+
+    @property
+    def bounds(self):
+        return self._bounds
+
+    def _getClipCursor(self):
+        bounds = wf.Bounds()
+        wf.GetClipCursor(bounds)
+
+        return bounds
+
+    @property
+    def clipped(self):
+        return (self._getClipCursor() == self._bounds)
+
+    def clip(self):
+        wf.ClipCursor(self._bounds)
+
+    def release(self):
+        wf.ClipCursor(None)
+
+    def toggle(self):
+        if self.clipped:
+            self.release()
+        else:
+            self.clip()

main.py

@@ -0,0 +1,87 @@
+#!/usr/bin/env python
+# coding: utf-8
+
+import sys, os
+
+from window import Window
+from cursor import Clip
+from ui import UI
+
+
+class App:
+    list_refresh_delay = 1 * 1000
+    clip_refresh_delay = 1 * 1000
+
+    def __init__(self):
+        self.windows = {}
+        self.selected_window = None
+        self.current_clip = None
+
+        self.ui = ui = UI('Trapper', self.resourcePath, self.list_refresh_delay)
+        ui.add_callback('getListOfWindows', self.getListOfWindows)
+        ui.add_callback('changeSelectedWindow', self.changeSelectedWindow)
+        ui.add_callback('clipCursor', self.clipCursor)
+        ui.add_callback('isClipped', self.isClipped)
+
+    def __del__(self):
+        Clip.clearClips()
+
+    @staticmethod
+    def resourcePath(relative):
+        basedir = sys._MEIPASS if getattr(sys, 'frozen', False) else os.path.dirname(__file__)
+        return os.path.join(basedir, relative)
+
+    def run(self):
+        self.ui.mainloop()
+
+    def getListOfWindows(self):
+        self.windows = {str(window): window for window in Window.getAllTaskbarWindows()}
+        windows = [(name, window == self.selected_window) for name, window in self.windows.items()]
+        return sorted(windows, key=lambda w: w[0])
+
+    def changeSelectedWindow(self, selection):
+        self.selected_window = self.windows.get(selection, None)
+
+    def clipCursor(self, selection):
+        self.selected_window = self.windows.get(selection, None)
+
+        if self.isClipped():
+            if self.current_clip:
+                self.current_clip.release()
+                self.current_clip = None
+
+            return False
+
+        elif self.selected_window:
+            self.current_clip = Clip(self.selected_window.bounds)
+            self.current_clip.clip()
+            self.ui.root.after(self.clip_refresh_delay, lambda: self.refreshClip(self.current_clip))
+
+            return True
+
+        return False
+
+    def refreshClip(self, previous_clip):
+        if (not self.current_clip) or self.current_clip != previous_clip:
+            return
+
+        if (not self.selected_window) or (not self.selected_window.exists):
+            return
+
+        window_bounds = self.selected_window.bounds
+        if previous_clip.bounds != window_bounds:
+            # window has moved, so get a new clip for the new coords
+            previous_clip.release()
+            self.current_clip = Clip(window_bounds)
+
+        self.current_clip.clip()
+        self.ui.root.after(self.clip_refresh_delay, lambda: self.refreshClip(self.current_clip))
+
+    def isClipped(self):
+        return (self.selected_window and self.selected_window.exists
+                and self.current_clip and self.current_clip.clipped)
+
+
+if __name__ == '__main__':
+    app = App()
+    app.run()

ui.py

@@ -0,0 +1,164 @@
+#!/usr/bin/env python
+# coding: utf-8
+
+from tkinter import *
+from tkinter.ttk import *
+
+
+class UI:
+    width = 550
+    height = 350
+    minwidth = 120
+    minheight = 90
+
+    def __init__(self, app_name, resource_path_func, list_refresh_delay):
+        self.list_refresh_delay = list_refresh_delay
+
+        self.windows = {}
+        self.callbacks = {}
+
+        self.root = root = Tk()
+        root.title(app_name)
+        root.geometry('{}x{}'.format(self.width, self.height))
+        root.minsize(self.minwidth, self.minheight)
+        root.iconbitmap(resource_path_func('icon.ico'))
+        root.columnconfigure(0, weight=1)
+
+        self.buttons = Buttons(root)
+
+        self.list = WindowsList(root)
+        root.rowconfigure(1, weight=1)
+
+        self.buttons.clip_button.configure(command=self.clip_button_clicked)
+        self.list.results_listbox.bind('<<ListboxSelect>>', self.selection_changed)
+        self.root.after(1, self.refreshWindowList)
+
+    @property
+    def mainloop(self):
+        return self.root.mainloop
+
+    def add_callback(self, key, callback):
+        self.callbacks[key] = callback
+
+    def remove_callback(self, key):
+        del self.callbacks[key]
+
+    def run_callback(self, key, *args):
+        return self.callbacks[key](*args)
+
+    def clip_button_clicked(self):
+        listbox = self.list.results_listbox
+
+        selection = listbox.curselection()
+        if not selection:
+            return
+
+        index = int(selection[0])
+        value = listbox.get(index)
+        clipping = self.run_callback('clipCursor', value)
+
+        self.refreshIfClipped(clipping)
+
+    def refreshIfClipped(self, is_clipped = None):
+        if is_clipped is None:
+            is_clipped = self.run_callback('isClipped')
+
+        button = self.buttons.clip_button
+        listbox = self.list.results_listbox
+        label = self.list.results_label
+
+        button_text = 'Unclip' if is_clipped else 'Clip'
+        button.configure(text=button_text)
+
+        listbox_state = DISABLED if is_clipped else NORMAL
+        listbox.configure(state=listbox_state)
+
+        if is_clipped:
+            label.grid()
+        else:
+            label.grid_remove()
+
+    def selection_changed(self, event):
+        listbox = event.widget
+        label = self.list.results_label
+
+        selection = listbox.curselection()
+        if not selection:
+            return
+
+        index = int(selection[0])
+        value = listbox.get(index)
+
+        label.config(text=value)
+
+        clipping = self.run_callback('changeSelectedWindow', value)
+
+    def refreshWindowList(self):
+        listbox = self.list.results_listbox
+        label = self.list.results_label
+        disabled = listbox.cget('state') == DISABLED
+
+        if disabled:
+            listbox.config(state=NORMAL)
+
+        listbox.delete(0, END)
+
+        for title, selected in self.run_callback('getListOfWindows'):
+            listbox.insert(END, title)
+            if selected:
+                label.config(text=title)
+                index = listbox.size() - 1
+                listbox.selection_set(index)
+                listbox.activate(index)
+
+        if disabled:
+            listbox.config(state=DISABLED)
+
+        self.refreshIfClipped()
+
+        self.root.after(self.list_refresh_delay, self.refreshWindowList)
+
+
+class Section(Frame):
+    def __init__(self, master=None):
+        Frame.__init__(self, master)
+        self.grid(sticky=N+E+W+S, padx=1, pady=1)
+        self.createWidgets()
+
+
+class Buttons(Section):
+    def createWidgets(self):
+        button = Button(self, text='Clip', style='TButton')
+        button.grid(sticky=N+E+W+S, padx=5, pady=5)
+
+        self.columnconfigure(0, weight=1)
+
+        self.clip_button = button
+
+
+class WindowsList(Section):
+    def createWidgets(self):
+        label = Label(self)
+        scrollbar = AutoScrollbar(self, orient=VERTICAL)
+        listbox = Listbox(self, yscrollcommand=scrollbar.set, exportselection=0)
+        scrollbar.config(command=listbox.yview)
+
+        label.grid(row=0, columnspan=2)
+        label.grid_remove()
+        listbox.grid(row=1, column=0, sticky=N+E+W+S)
+        scrollbar.grid(row=1, column=1, sticky=N+S)
+        self.columnconfigure(0, weight=1)
+        self.rowconfigure(1, weight=1)
+
+        self.results_label = label
+        self.results_listbox = listbox
+
+
+class AutoScrollbar(Scrollbar):
+    def set(self, low, high):
+        if float(low) <= 0.0 and float(high) >= 1.0:
+            self.grid_remove()
+        else:
+            self.grid()
+
+        Scrollbar.set(self, low, high)