Add grayscale angle shading option for 2D spiral view

[kryptokommunist]

Summary

• add advanced toggle to shade 2D spiral regions by normalized line angle in grayscale
• introduce render logic to compute grayscale fills from line angles while preserving outlines and pattern options
• expose new shading parameter in default settings and normalization

Testing

• not run

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Codex Task

[gemini-code-assist]

Summary of Changes

Hello @kryptokommunist, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a new visual rendering option for the 2D spiral view, allowing users to color regions based on the orientation of their constituent lines. This enhancement provides an alternative way to visualize the underlying structure of the spirals by mapping line angles to a grayscale intensity, offering a unique perspective on the generated patterns. It involves updates to the UI, default settings, and the core rendering engine to support this new shading mode.

Highlights

• New Feature: Grayscale Angle Shading: Introduced an advanced option to shade 2D spiral regions by their normalized line angle, rendering them in grayscale from black to white.
• User Interface Integration: Added a new checkbox in the 'Advanced settings' section of the HTML interface, allowing users to toggle the 'Colour 2D regions by line angle (grayscale)' feature.
• Enhanced Rendering Logic: Implemented core rendering logic within DoyleSpiralEngine to calculate grayscale values based on arc group line angles and apply them as solid fills, ensuring outlines are preserved and this shading method is mutually exclusive with existing pattern fills.
• Configuration and Normalization: Integrated the new shade_by_angle parameter into the application's default settings and the parameter normalization process, ensuring consistent behavior across the application.

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[gemini-code-assist]

Code Review

This pull request introduces a new feature allowing users to color 2D regions by their line angle in grayscale. The changes include adding a 'Colour 2D regions by line angle (grayscale)' checkbox and a descriptive hint to the index.html user interface. The app.js file was updated to include shade_by_angle: false in the default settings. In doyle_spiral_engine.js, the ArcGroup class was extended to support solid fills with opacity, and the _createArcGroupsForCircles and render methods were modified to accept and process a new shadeByAngle parameter. When shadeByAngle is active, the system now calculates a grayscale color based on the normalized line angle of each arc group and applies it as a solid fill, while conditionally suppressing traditional pattern fills and outlines to prevent conflicts. Finally, the normaliseParams and renderSpiral functions were updated to correctly handle the new shade_by_angle parameter.