Compiling a static library for Windows

sashkent3 · July 4, 2025, 10:47am

I’m experimenting with WebRTC in Defold using the libdatachannel library in a native extension. Its build process seems rather complicated, as far as I understand the Defold’s extender has no support for CMake or anything like that. So I’m trying to build libdatachannel as a static library.
Despite the conflicts with Defold’s version of mbedtls, I have a working prototype on Linux. Now I want to build it for Windows as well.
To achieve maximum portability, I believe it’s necessary to reproduce the extender’s build environment precisely. What compiler should I use? What MSVC version to target? Is it better to build on Windows or should cross-compilation on Linux work as well?
Any suggestions for a smooth portable compilation pipeline are much appreciated.

sashkent3 · July 14, 2025, 10:34am

Regarding the mbedtls conflict, I’ve opened a separate issue on Defold’s GitHub. The solution proposed there seems promising. I’ll post an update there once I try it out soon.
This is, however, only a small part of my initial question. Fundamentally, I’m still very interested in ways to portably compile a large C++ project as a Windows static library for a Native Extension.
What build environment and compiler should I choose? What build environment and compiler does Defold use when building a Defold project for Windows?

britzl · July 14, 2025, 10:58am

The engine versions included in each release are built using GitHub Actions:

github.com/defold/defold

.github/workflows/main-ci.yml

dev


      
          bld-eng-windows:
            strategy:
              matrix:
                platform: [win32, x86_64-win32]
          
            runs-on: windows-latest
            timeout-minutes: 30
            steps: [
              { name: 'Checkout', uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11, with: { ref: '${{env.BUILD_BRANCH}}' } },
              { name: 'Install Python', uses: actions/setup-python@0a5c61591373683505ea898e09a3ea4f39ef2b9c, with: { python-version: 3.13} },
              { name: 'Install Java', uses: actions/setup-java@99b8673ff64fbf99d8d325f52d9a5bdedb8483e9, with: { java-version: '21.0.5+11.0.LTS', distribution: 'temurin'} },
              { name: 'Setup dotnet', uses: actions/setup-dotnet@v4, with: {dotnet-version: '9.x'}},
              { name: 'Install dependencies', shell: bash, run: 'ci/ci.sh install --platform=${{ matrix.platform }}' },
              {
                name: 'Build engine',
                if: (github.event_name != 'repository_dispatch') || ((github.event_name == 'repository_dispatch') && (github.event.client_payload.skip_engine != true)),
                shell: bash,
                run: 'ci/ci.sh --platform=${{ matrix.platform }} --archive --skip-builtins --skip-docs engine'
              },
              {

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For Windows builds we use windows-latest which at the moment happens to be Windows Server 2022:

We build using a prepackaged tool chain from Visual-Studio 2022 14.37.32822:

github.com/defold/defold

build_tools/sdk.py

dev


      
          ## **********************************************************************************************
          # Win32
          
          # The version we have prepackaged
          VERSION_WINDOWS_SDK_10="10.0.20348.0"
          VERSION_WINDOWS_MSVC_2022="14.37.32822"
          PACKAGES_WIN32_TOOLCHAIN=f"Microsoft-Visual-Studio-2022-{VERSION_WINDOWS_MSVC_2022}"
          PACKAGES_WIN32_SDK_10=f"WindowsKits-{VERSION_WINDOWS_SDK_10}"

For setting things up yourself also see instructions here:

github.com/defold/defold

README_SETUP.md

dev

# Engine setup

(Setup instructions for the editor [here](/editor/README.md)).

This guide focuses on the tool and platform sdk installation.

Build instructions for the engine are found here [here](/editor/README_BUILD.md)).

At the very minimum, you need to install the SDK for your host platform (Windows, macOS or Linux)

## Supported hosts + targets

Here is a table of our supported target platforms, and on which host platform you can build it:

|host↓  target→ | macOS | Linux | Windows | Android | iOS     | Hmtl5   | PS4/PS5 | Switch | XBox  |
|--------------|-------|-------|---------|---------|---------|---------|---------|--------|-------|
|macOS         | ✅    |       |         | ✅      | ✅      | ✅     |         |        |       |
|Linux         |       | ✅    |         | ✅      |         | ✅      |         |        |       |
|Windows (x64) |       |       | ✅      | ✅      |         |         | ✅      | ✅     | ✅    |

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sashkent3 · July 14, 2025, 12:43pm

@britzl thank you, this is very insightful! For some reason, I haven’t thought of checking the build instructions for the engine itself.
Is this essentially the same build environment that Defold’s Extender uses when compiling Native Extensions? Presumably, that one I should actually target.

britzl · July 15, 2025, 4:46am

Yes, they are indeed very similar. But remember that many native extensions comes with precompiled libraries and we have no control over how they were created. You do not have to be super strict about getting everything exactly the same.