Fix the Pen tool preview segment disappearing during repeated undo

[krVatsal]

Fixes #3790

[gemini-code-assist]

Summary of Changes

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This pull request addresses a bug in the Pen tool where the preview line would become invisible or incorrectly positioned after performing multiple undo actions. The changes ensure that the tool's internal state correctly reflects the current drawing context after an undo, specifically by retaining the FSM state during anchor placement and explicitly updating the bezier curve preview's origin and handles. This provides a more consistent and predictable user experience when using the Pen tool with undo functionality.

Highlights

• Pen Tool State Retention: Modified the Pen tool's anchor placement logic to ensure the Finite State Machine (FSM) retains its current state instead of resetting to Ready when place_anchor returns None.
• Undo Preview Fix: Implemented a fix for the Pen tool's preview line to remain visible and correctly positioned after multiple undo operations by synchronizing preview state variables (next_point, next_handle_start, handle_end) and triggering a PointerMove message.

Changelog

• editor/src/messages/tool/tool_messages/pen_tool.rs
  • Changed place_anchor's unwrap_or fallback to self to maintain the current FSM state.
  • Added logic within the Undo message handler to decrement point_index and synchronize next_point, next_handle_start, and handle_end based on the new point_index.
  • Introduced a PointerMove message dispatch after an undo to immediately update the preview line's position to follow the cursor.

Activity

• The pull request description indicates it fixes issue Pen tool preview line disappearing during repeated undo #3790.

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[gemini-code-assist]

Code Review

The pull request improves the Pen tool's preview visibility during undo operations by ensuring the internal state is correctly synchronized. However, the updated undo logic introduces a regression where the tool no longer aborts when undoing the first anchor point. This should be corrected to maintain consistent behavior when canceling a path creation.

[dhruvjamwal]

I just reviewed the regression on PR #3791 regarding the Pen tool undo logic. Please update for further changes.

[cubic-dev-ai]

No issues found across 1 file

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

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