Implement brush previews

README.md

@@ -37,6 +37,7 @@ This is a TUI (Text User Interface) image editor, inspired by MS Paint, and buil
 - [x] Undo/Redo
 - [x] Efficient screen updates and undo/redo history, by tracking regions affected by each action
 	- You could totally use this program over SSH! Haha, this "what if" project could actually be useful. Of course, it should be mentioned that you can also run graphical programs over SSH, but this might be more responsive, or just fit your vibe better.
+- [x] Brush previews
 - [x] Menu bar
 
 ## Development

paint.py

@@ -2,7 +2,7 @@ import re
 import sys
 from enum import Enum
 from random import randint, random
-from typing import List
+from typing import List, Optional
 import stransi
 from rich.segment import Segment
 from rich.style import Style
@@ -498,6 +498,13 @@ class Canvas(Widget):
             self.mouse_move_event = mouse_move_event
             super().__init__()
 
+    class ToolPreviewUpdate(Message):
+        """Message when moving the mouse while the mouse is up."""
+
+        def __init__(self, mouse_move_event: events.MouseMove) -> None:
+            self.mouse_move_event = mouse_move_event
+            super().__init__()
+
     def __init__(self, **kwargs) -> None:
         """Initialize the canvas."""
         super().__init__(**kwargs)
@@ -517,6 +524,8 @@ class Canvas(Widget):
 
         if self.pointer_active:
             self.post_message(self.ToolUpdate(event))
+        else:
+            self.post_message(self.ToolPreviewUpdate(event))
 
     def on_mouse_up(self, event) -> None:
         self.pointer_active = False
@@ -579,6 +588,7 @@ class PaintApp(App):
 
     undos: List[Action] = []
     redos: List[Action] = []
+    preview_action: Optional[Action] = None
 
     NAME_MAP = {
         # key to button id
@@ -728,6 +738,7 @@ class PaintApp(App):
     def on_canvas_tool_start(self, event: Canvas.ToolStart) -> None:
         """Called when the user starts drawing on the canvas."""
         event.stop()
+        self.cancel_preview()
 
         if self.selected_tool == Tool.pick_color:
             self.pick_color(event.mouse_down_event.x, event.mouse_down_event.y)
@@ -756,9 +767,32 @@ class PaintApp(App):
             action.update(self.image_at_start)
             self.canvas.refresh(affected_region)
 
+    def cancel_preview(self) -> None:
+        """Revert the currently previewed action."""
+        if self.preview_action:
+            self.preview_action.undo(self.image)
+            self.canvas.refresh(self.preview_action.region)
+            self.preview_action = None
+
+    def on_canvas_tool_preview_update(self, event: Canvas.ToolPreviewUpdate) -> None:
+        """Called when the user is hovering over the canvas but not drawing yet."""
+        event.stop()
+        self.cancel_preview()
+
+        if self.selected_tool in [Tool.brush, Tool.pencil, Tool.eraser]:
+            image_before = AnsiArtDocument(self.image.width, self.image.height)
+            image_before.copy_region(self.image)
+            affected_region = self.stamp_brush(event.mouse_move_event.x, event.mouse_move_event.y)
+            if affected_region:
+                self.preview_action = Action(self.selected_tool.get_name(), self.image)
+                self.preview_action.region = affected_region.intersection(Region(0, 0, self.image.width, self.image.height))
+                self.preview_action.update(image_before)
+                self.canvas.refresh(affected_region)
+
     def on_canvas_tool_update(self, event: Canvas.ToolUpdate) -> None:
         """Called when the user is drawing on the canvas."""
         event.stop()
+        self.cancel_preview()
 
         if self.selected_tool == Tool.pick_color:
             self.pick_color(event.mouse_move_event.x, event.mouse_move_event.y)
@@ -767,6 +801,13 @@ class PaintApp(App):
         if self.selected_tool in [Tool.fill, Tool.magnifier]:
             return
         
+        if len(self.undos) == 0:
+            # This can happen if you undo while drawing.
+            # Ideally we'd stop getting events in this case.
+            # This might be buggy if there were multiple undos.
+            # It might replace the action instead of doing nothing.
+            return
+
         mm = event.mouse_move_event
         action = self.undos[-1]
         affected_region = None