NeoCalc (The "Why Do We Exist" Fork)

Originally created as a simple calculator to teach kids how to program. It was simple. It was pure. It added 2 and 2 and got 4.

But then I came along. I saw a perfectly functional teaching tool and thought, "You know what this needs? Unnecessary complexity and a bad attitude." So I forked it, injected it with Rust, and stripped it of its innocence.

Features

• Rust Backend: Powered by neocalc-core via UniFFI for high performance and safety.
• Fraction Support: Toggle between precise fractional (e.g., 1/2) and decimal (e.g., 0.5) outputs in Settings.
• 4 Calculator Modes: Standard, Scientific, Programming, and Financial.
• Responsive Layout: Works in Portrait and Landscape (Split View).
• Theming Engine: Import your own .css themes (GTK-compatible).
• Dark Mode: By default, because we respect your eyes.

Installation / Downloads

You can download the latest Android APK from the Releases Page.

1. Download neocalc-release.apk.
2. Install it on your Android device (you may need to allow installation from unknown sources).
3. Calculate away your existential dread.

Versioning Scheme

We use a Date-Based Versioning scheme to keep things fresh:

vYEAR.MONTH-REVISION

• YEAR: The current year (e.g., 2025).
• MONTH: The current month (e.g., 12).
• REVISION: An incrementing number for releases within that month (e.g., 1, 2, 5).

Example: v2025.12-5 is the 5th release in December 2025.

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Theming Guide: How to Create Custom Themes

NeoCalc supports custom themes defined in simple .css files. These themes are compatible with the original GTK version of the app.

How to Import a Theme

1. Create a .css file on your phone (e.g., my-cool-theme.css).
2. Open NeoCalc.
3. Tap the Brush Icon in the top bar.
4. Tap "Import Theme".
5. Select your .css file.

CSS Format

The theme parser looks for specific @define-color lines. Format: @define-color KEY #HEXCODE;

Theme Keys Reference

Key	Description	Android UI Mapping
Window Colors
window_bg_color	Main background color of the app.	App Background
window_fg_color	Default text color.	Default Text
Number Buttons
card_bg_color	Background for number buttons (0-9).	Secondary Container
card_fg_color	Text color for numbers.	On Secondary Container
Operator Buttons
warning_bg_color	Background for operators (+, -, /, x).	Tertiary Container
warning_fg_color	Text color for operators.	On Tertiary Container
Function Buttons
headerbar_bg_color	Background for functions (Sin, Cos, Log).	Surface Variant
headerbar_fg_color	Text color for functions.	On Surface Variant
Accent / Equals
accent_bg_color	The "Equals" (=) button background.	Primary
accent_fg_color	Text on the Equals button.	On Primary
Destructive
destructive_bg_color	Delete / Clear button background.	Error Container
destructive_fg_color	Delete / Clear button text.	On Error Container

Example Theme (dracula.css)

@define-color window_bg_color #282a36;
@define-color window_fg_color #f8f8f2;

@define-color headerbar_bg_color #44475a;
@define-color headerbar_fg_color #f8f8f2;

@define-color card_bg_color #6272a4;
@define-color card_fg_color #f8f8f2;

@define-color accent_bg_color #bd93f9;
@define-color accent_fg_color #282a36;

@define-color warning_bg_color #ffb86c;
@define-color warning_fg_color #282a36;

@define-color destructive_bg_color #ff5555;
@define-color destructive_fg_color #282a36;

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Building from Source

Prerequisites

• Android Studio (Ladybug or newer recommended)
• Rust (rustup installed)
• JDK 17

Build Commands

Ensure you have initialized the submodules before building:

git submodule update --init --recursive

The build process automatically compiles the Rust backend (via the mobile_backend wrapper crate) and generates Kotlin bindings.

cd android
./gradlew assembleDebug

The APK will be found in android/app/build/outputs/apk/debug/app-debug.apk.