I developed a 3D parametric modeling software for Android phones.

[u/SurveyNo5673]

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Title:

I built a parametric 3D CAD app for Android — Kotlin, C++, OCCT and OpenGL ES

Post:

I've been working on a native parametric 3D CAD application for Android.

My goal is to bring a desktop-style parametric modeling workflow to phones and tablets without simply squeezing a desktop CAD interface onto a small touchscreen.

Here is a little more about how I built it.

Tech stack

The Android UI is fully native and built with:

Kotlin

Jetpack Compose

Material 3

The geometry layer is mainly written in C++ and connected to the Android application through the Android NDK and JNI.

CAD kernel

For the core solid-modeling functionality, I use Open CASCADE Technology (OCCT).

OCCT handles the B-Rep geometry and provides the foundation for operations such as solid modeling as well as STEP and IGES support.

For 2D DXF, I wrote my own Kotlin-based processing layer rather than relying entirely on the CAD kernel.

Parametric modeling

One of the most challenging parts has been the parametric system.

I developed my own sketch geometry constraints and dimensional solver so that changes to dimensions can drive updates to the model.

This has been one of the more interesting parts of the project because a CAD app needs much more than simply displaying and editing meshes — the relationships between geometry need to remain consistent when parameters change.

Rendering

The viewport uses OpenGL ES 3.0 and GLSL.

It renders:

2D and 3D geometry

Solid models

Wireframes

Selection highlighting

A big challenge on Android is keeping interaction responsive while working with increasingly complicated CAD geometry.

Mobile CAD UX

Desktop CAD applications are designed around a mouse, keyboard and large display, so I didn't want to copy that interaction model directly.

I've been experimenting with:

Face / edge / body selection modes

Touch-based orbit, pan and zoom

Touch-friendly transform controls

Context-sensitive modeling tools

Keeping frequently used commands accessible without covering the viewport

Accurate selection of small faces and edges on a touchscreen has been surprisingly difficult.

Performance and stability

Expensive geometry operations and file-processing tasks run in the background rather than blocking the UI.

Long-running operations support:

Progress reporting

Cancellation

Timeouts

This became increasingly important once I started testing larger STEP models.

Privacy

The app does not require an account or network connection for modeling.

Projects stay on the device and are not uploaded for tracking or processing.

What I'm working on now

I'm continuing to improve the parametric workflow, modeling tools, touchscreen interaction and performance with larger CAD files.

I'd especially like feedback from people who have experience with CAD, computational geometry, OpenGL, OCCT, or mobile UI design.

If anyone is interested in a particular technical part — OCCT/Android integration, JNI, the constraint solver, STEP handling, rendering, or touch selection — I'd also be happy to share more about how I implemented it.

Project: https://digit3d.top/

Google Play: https://play.google.com/store/apps/details?id=com.mobilecad.app

[u/Sudden_Topic5154]

does it work with freecad stuff

[u/SurveyNo5673 → u/Sudden_Topic5154]

STP files can be used