de-rossi-consulting/logisim.app

Purpose and Entry Points

Logisim.app ports Logisim 2.7.2, a digital-circuit design and simulation desktop application, to modern browsers. The browser shell starts from index.html and JavaScript under src/javascript/main.js; it loads and executes the prebuilt Java application at public/logisim.jar through CheerpJ/WebAssembly.

Browser Host Layer

The Vite-served frontend provides the page, styling, runtime bootstrap, alerts, examples, and browser-specific file integration.

• index.html

• src/javascript/main.js

• src/javascript/fileFunctions.js

This layer is the boundary between browser APIs and the Java application. It supports local-file interactions and a browser virtual filesystem backed by IndexedDB; browser restrictions alter save behavior, especially in Firefox.

Java Application Startup and UI

The primary application remains a Java/Swing program. com.cburch.logisim.Main is the Java-level application entry point, with startup mode/UI initialization separated under the start package. Main editing, menus, canvas painting, tool selection, and simulation controls reside in the GUI packages.

• logisim/src/com/cburch/logisim/Main.java

• logisim/src/com/cburch/logisim/gui/start/Startup.java

• logisim/src/com/cburch/logisim/gui/main/Frame.java

Circuit Domain Model and Simulation

Circuit construction is modeled independently of the UI: circuits contain components, wires, mutations, transactions, and per-run state. The simulator and propagator evaluate signal changes, while ticker support drives clocked circuits. This is the core control flow from user edits or input changes to recalculated component values and rendered simulation state.

• logisim/src/com/cburch/logisim/circuit/Circuit.java

• logisim/src/com/cburch/logisim/circuit/Simulator.java

• logisim/src/com/cburch/logisim/circuit/Propagator.java

Components, Libraries, and Instance Contract

Reusable component factories and instances form the extensibility boundary. Standard libraries implement gates, arithmetic, wiring, I/O, multiplexers, and stateful memory; each uses shared component/instance abstractions for ports, attributes, painting, and simulation behavior.

• logisim/src/com/cburch/logisim/instance/InstanceFactory.java

• logisim/src/com/cburch/logisim/std/Builtin.java

• logisim/src/com/cburch/logisim/std/memory/Memory.java

Project Persistence and Analysis

Projects and circuit libraries are loaded/saved through Logisim XML readers/writers and loaders. The analysis subsystem derives truth tables and Boolean expressions from circuit-level logic and can build circuits from analyzed expressions.

• logisim/src/com/cburch/logisim/file/LogisimFile.java

• logisim/src/com/cburch/logisim/file/XmlReader.java

• logisim/src/com/cburch/logisim/analyze/model/AnalyzerModel.java

Build, Runtime, and Assets

Java 8+ and Python build the Java sources into the deployable JAR; Node/Vite serves the browser host. CheerpJ is the material external runtime enabling Java bytecode execution via WebAssembly. Bundled JAR dependencies and localized resources remain part of the Java distribution.

• logisim/scripts/create-jar.py

• public/logisim.jar

• logisim/libs/jh.jar