Fix svg cursor position

[oscartbeaumont]

Summary by CodeRabbit

• Bug Fixes

  • Corrected an issue with cursor color rendering to ensure accurate color display.

• Improvements

  • Enhanced cursor scaling and positioning for more precise alignment and consistent appearance at different zoom levels.
  • Improved SVG cursor rendering for better visual quality.

• Documentation

  • Added detailed explanations for coordinate system markers to clarify rendering pipeline semantics.

• New Features

  • Enabled in-place subtraction operations for coordinate and position types to support more flexible manipulations.

[coderabbitai]

Walkthrough

The logic for cursor size and position calculation in the rendering layer was revised. Zoom scaling is now applied after determining the base cursor size, and the hotspot offset is recalculated at an earlier stage. The SVG cursor preparation was simplified, and a bug in pixel color extraction was corrected. Additionally, SubAssign trait implementations were added for generic coordinate and configuration structs, and detailed documentation was added for coordinate system marker structs. An unused coordinate space struct was removed.

Changes

Cohort / File(s)	Change Summary
Cursor Size, Position, and SVG Preparation crates/rendering/src/layers/cursor.rs	Adjusted cursor size calculation to apply zoom scaling later, recalculated hotspot offset, simplified SVG scaling, and fixed RGBA color extraction bug.
Coordinate System Enhancements and Trait Implementation crates/rendering/src/coord.rs	Added detailed documentation for coordinate system marker structs, removed unused TransformedDisplaySpace struct, and implemented SubAssign for Coord<T>.
Configuration Trait Implementation crates/project/src/configuration.rs	Added SubAssign trait implementation for generic XY<T> struct to enable in-place subtraction of coordinates.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

A cursor hops, now sized just right,
With zoom and clicks, it takes new flight.
SVGs scale with gentle care,
And colors fixed from here to there.
Coordinates now neatly aligned,
Traits assigned and docs refined.
A pixel-perfect leap for bunny and me! 🐇✨

Note

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Learn more here, or try it out under "Finishing Touches" below.

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📜 Recent review details

Configuration used: CodeRabbit UI
Review profile: CHILL
Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between a220703 and 950d96b.

📒 Files selected for processing (3)

• crates/project/src/configuration.rs (2 hunks)
• crates/rendering/src/coord.rs (2 hunks)
• crates/rendering/src/layers/cursor.rs (4 hunks)

🚧 Files skipped from review as they are similar to previous changes (1)

• crates/rendering/src/layers/cursor.rs

🔇 Additional comments (5)

crates/project/src/configuration.rs (2)

2-2: LGTM - Import addition is correct.

The SubAssign trait import is properly added to support the new trait implementation.

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151-159: LGTM - SubAssign implementation is correct.

The implementation properly performs in-place subtraction of x and y components with appropriate trait bounds. This complements the existing arithmetic operations and follows Rust conventions.

crates/rendering/src/coord.rs (3)

1-1: LGTM - SubAssign import properly added.

The SubAssign trait import is correctly added to support the new trait implementation.

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7-40: Excellent documentation additions.

The detailed documentation for coordinate system marker structs significantly improves code clarity by:

• Clearly defining the origin point (0,0) for each coordinate system
• Explaining relationships and transformations between different spaces
• Providing context for when each coordinate system is used

This is particularly valuable for a rendering pipeline where coordinate transformations are critical to correctness.

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180-184: LGTM - SubAssign implementation is correct.

The implementation properly performs in-place subtraction on the coord field while preserving the space marker. This complements the existing arithmetic operations and leverages the SubAssign implementation from XY.

✨ Finishing Touches

• 📝 Generate Docstrings

🧪 Generate unit tests

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix-svg-cursor-position

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