7. MarkUs: Touch Annotations

For the first time, grading on iPads, Surface tablets, and touchscreen laptops just works.

PR #7736 (In Progress)

The Work

Added touch event support for annotations:

• touchstart / touchmove / touchend handlers for PDF annotation manager
• Same handlers for image annotation manager
• Refactored mouse/touch event handling to shared helpers
• Cleaned up coordinate logic
• Switched to addEventListener to fix touchmove issues
• Reduced JS duplication significantly
• Updated changelog

The Impact

Grading now works on:

• iPads
• Surface tablets
• Android tablets
• Touchscreen laptops

This is critical as more instructors grade on tablets. Before this PR, touch users couldn’t draw annotation boxes at all.

What It Taught Me

Event model nuances — Mouse and touch events have different properties, different coordinate systems, different default behaviors. You can’t just swap click for touchstart.

Legacy JS refactoring — The annotation code was old. Touch support couldn’t just be bolted on; it required understanding and cleaning up existing code.

Parallel code paths — PDF and image annotation managers had similar but not identical code. Review feedback applied to both.

Browser behavior debugging — “It works in Chrome but not Safari” is a real problem with touch events. Different browsers, different quirks.

Mobile grading was a known pain point for years. Fixing it meant understanding code written long before I joined.