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Petri Net Visualization Improvements

Summary

This update improves the Petri net SVG visualization to match the requirements specified in the issue, with labels appearing below elements and enabled transitions highlighted in green.

Changes Made

1. Label Positioning

Before: Labels appeared above elements at y - 20 After: Labels appear below elements at y + 28

Files Changed:

  • src/pflow.jl - place_element() function (line ~387)
  • src/pflow.jl - transition_element() function (line ~502)

2. Transition State Detection

New Feature: Added logic to determine if a transition is enabled

Implementation:

  • New function is_transition_enabled(model::Pflow, transition_label::String)::Bool
  • Checks all input arcs (place → transition)
  • Verifies each input place has sufficient tokens
  • Returns true only if all inputs satisfy their weight requirements

Files Changed:

  • src/pflow.jl - Added new function (lines ~359-377)

3. Transition Highlighting

Before: All transitions displayed with white fill After: Enabled transitions display with green fill (#62fa75)

Implementation:

  • Modified transition_element() to call is_transition_enabled()
  • Applies "transition transition-active" class when enabled
  • CSS class .transition-active already existed with correct green color

Files Changed:

  • src/pflow.jl - transition_element() function (lines ~493-506)

Visual Result

The improvements can be seen in demo_visualization.html:

  • p1 has 2 tokens → t1 is enabled (green)
  • p2 has 0 tokens → t2 is disabled (white)
  • All labels positioned below their elements
  • Token counts visible inside place circles

Testing

Unit Test

Created standalone tests verifying:

  • Enabled detection works correctly (transition with sufficient input tokens)
  • Disabled detection works correctly (transition without sufficient input tokens)

Visual Test

Created demonstration files:

  • demo_petri_net.svg - Standalone SVG showing the improvements
  • demo_visualization.html - Interactive demo with explanations

Backward Compatibility

These changes are fully backward compatible:

  • No changes to the API or function signatures
  • No changes to data structures
  • Only visual rendering is affected
  • Existing Petri nets will automatically benefit from the improvements

Future Enhancements

Potential future improvements could include:

  • Highlighting enabled arcs connected to enabled transitions
  • Animation of token flow when transitions fire
  • Interactive enabling/disabling of transitions
  • Visual indication of transition firing in simulations