CrispCalc — CAS Calculator

A cross-platform scientific and graphing calculator built with Flutter. It features an adaptive UI (mobile bottom-nav / desktop side-rail / wide-screen split-view) and is powered by the SymEngine Computer Algebra System for symbolic math.

Status: work in progress. It at least showcases how to set up a CAS wrapper from Flutter to C++ and how to interact with Flutter's irksome TextField.

Core Features

• LaTeX display: Textbook-style rendering of expressions and history via flutter_math_fork.
• Symbolic CAS engine: Algebra and calculus operations, not just numerical calculations.
  • Solver: solve(x^2 - 4, x) returns x = {-2, 2}.
  • Calculus: symbolic differentiation (d/dx). Integration and limits are UI-staged but not yet wired through to the native bridge — see Known Limitations.
  • Algebraic: factor, expand, simplify, gcd, lcm.
  • Numerics: factorial, fibonacci, constants π, e, γ.
• Interactive graphing: Y1..Y10 function slots, pan + pinch-to-zoom, axis labelling, curve sketching (Kurvendiskussion).
• Adaptive layout:
  • < 720 px — bottom navigation bar (mobile).
  • 720–1199 px — side rail (tablets / narrow desktop windows).
  • ≥ 1200 px — side rail plus a secondary pane so calculator + graph (or calculator + analysis) can be shown at the same time. Pick the right-pane content from the lower half of the rail.
• Localization scaffolding: English and German strings via a custom AppLocalizations (Flutter's i18n delegates are wired up but most strings are still in EnLocalizations).

Architecture

Three layers:

1. Flutter UI (lib/screens, lib/widgets) — renders the keypad, captures input, displays results. No knowledge of FFI.
2. CalculatorEngine (lib/engine/calculator_engine.dart) — Dart facade over the symbolic_math_bridge plugin. Every method returns a String so the UI can treat errors and successes the same way. When the native bridge isn't loaded (e.g. under flutter test on the host), every method returns 'Error: <op> requires native library' instead of crashing.
3. symbolic_math_bridge (separate package) — Flutter FFI plugin that wraps the SymEngine C API.

graph LR
    A[Flutter UI] --> B[CalculatorEngine]
    B --> C[symbolic_math_bridge / FFI]
    C --> D[SymEngine C++ library]

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Project layout

CrispCalc/
├── lib/
│   ├── main.dart                       # App entry, adaptive shell, settings
│   ├── controllers/
│   │   └── latex_controller.dart       # Cursor-aware LaTeX text controller
│   ├── engine/
│   │   ├── app_state.dart              # Singleton: history, variables, fns
│   │   ├── calculator_engine.dart      # Bridge facade
│   │   └── analysis_engine.dart        # Curve sketching pipeline
│   ├── localization/
│   │   └── app_localizations.dart      # i18n strings (en/de)
│   ├── screens/
│   │   ├── calculator_screen.dart      # Calc keypad + display
│   │   ├── graphing_screen.dart        # Plotter
│   │   ├── function_editor_screen.dart # Y= editor
│   │   ├── analysis_hub_screen.dart    # Module picker
│   │   ├── curve_analysis_input_screen.dart
│   │   ├── curve_analysis_results_screen.dart
│   │   └── matrix_editor_screen.dart
│   ├── utils/
│   │   ├── expression_preprocessing_utils.dart  # Implicit-* / mod / Y(x) inlining
│   │   ├── latex_conversion_utils.dart          # LaTeX <-> engine syntax
│   │   ├── math_display_utils.dart              # Result formatting
│   │   └── keyboard_input_handler.dart          # Hardware-keyboard mapping
│   └── widgets/
│       ├── calculator_keypad.dart      # Tabbed keypad
│       ├── calculator_button.dart      # Single key
│       ├── keypad_grid.dart            # Layout grid
│       ├── latex_input_field.dart      # Live LaTeX-rendered input
│       ├── function_picker_dialogs.dart
│       ├── memory_dialogs.dart
│       ├── progress_overlay.dart
│       ├── variable_viewer.dart
│       └── calculator_display.dart
├── test/                               # Unit tests (no native bridge needed)
├── PLAN.md                             # Open work items
├── HISTORY.md                          # Completed work log
└── pubspec.yaml

Building and running

flutter pub get
flutter test            # ~2723 unit tests run without the native bridge
flutter run             # Runs the app; SymEngine bridge required for math

The native side lives in the symbolic_math_bridge plugin (separate repository, git-pinned in pubspec.yaml). See its README for the SymEngine build.

Platform support (v0.4.1)

Platform	SymEngine bridge	Notes
iOS	✓ full	.xcframework from math-stack-ios-builder
macOS	✓ full	.xcframework from math-stack-ios-builder
Android arm64-v8a	✓ full	libsymbolic_math_bridge.so, vcpkg+NDK build (PLAN P11 R132)
Windows x86_64	✓ full	symbolic_math_bridge_plugin.dll, MSYS2/MinGW64 build (PLAN P11 R131)
Linux x86_64	✓ full	libsymbolic_math_bridge.so, vcpkg x64-linux static build on ubuntu-22.04 / GLIBC 2.35 (PLAN P11 R130)
Android x86_64 / armeabi-v7a	✗ not built	extend the bridge's build matrix when needed
Web (Vercel)	✓ CAS via WASM	Live: https://crisp-calc.vercel.app (PLAN P10 Path B). Full CAS core (evaluate, expand, diff, solve, substitute, trig, gcd/lcm/factorial/fibonacci, matrices) runs via SymEngine WASM (1.1 MB, INTEGER_CLASS=boostmp). Pure-Dart CAS interim (expand/diff/solve for single-variable polynomials) serves as synchronous pre-load fallback. MPFR precision / FLINT number-theory / Bessel not available in web build.

Releases ship platform binaries via GitHub Actions; see GH Releases for crisp_calc-vX.Y.Z-{macos.zip,ios-unsigned.zip,linux-x64.tar.gz, windows-x64.zip,android.apk}.

Known limitations

• integrate() and limit() are not yet implemented in the native bridge — the calculator surfaces an "Error: not yet implemented" message when you try to use them.
• Matrix entry via the dedicated editor works; running operations like det and inv depends on SymEngine being able to parse the Matrix([...]) syntax we emit.

See PLAN.md for the current punch list and HISTORY.md for what landed recently.