Looking for a crate with software rendering implementation of OpenGL

matklad · August 16, 2023, 9:30am

I am using

which provides painting API on top of OpenGL. I'd love to "unit-test" my app by essentially taking screenshots. I think what I need here is a software implementation of OpenGL, so that it can deterministically render my stuff to an image and just compare hashes of the result.

Is there a crate for this?

bjorn3 · August 16, 2023, 10:54am

I don't know of a rust crate, but you could use Mesa's LlvmPipe software OpenGL renderer and if necessary run your program inside xvfb (X virtual framebuffer) to be able to open a window while still running headless.

bjorn3 · August 16, 2023, 10:58am

Bevy roughly does this (except with LavaPipe rather than LlvmPipe for Vulkan support. LavaPipe requires a very new mesa version) Bevy also has some code to handle making screenshots and to read inputs from a file.

github.com

bevyengine/bevy/blob/3aad5c6b994f61b86fff08c28a868d80aad7d6fc/.github/workflows/ci.yml#L166


      
                  # Full git history is needed to get a proper list of changed files within `super-linter`
                  fetch-depth: 0
              - name: Run Markdown Lint
                uses: docker://ghcr.io/github/super-linter:slim-v4
                env:
                  MULTI_STATUS: false
                  VALIDATE_ALL_CODEBASE: false
                  VALIDATE_MARKDOWN: true
                  DEFAULT_BRANCH: main
          
          run-examples:
            runs-on: ubuntu-latest
            timeout-minutes: 30
            steps:
              - name: Install Bevy dependencies
                run: |
                  sudo apt-get update;
                  DEBIAN_FRONTEND=noninteractive sudo apt-get install --no-install-recommends -yq \
                    libasound2-dev libudev-dev;
              - name: install xvfb, llvmpipe and lavapipe
                run: |

jofas · August 16, 2023, 12:22pm

Maybe the easiest solution would be to ask the developers of Speedy2D to add an API for getting the raw pixels from a Graphics2D instance? AFAICT, they already have a private API for that (which I assume wraps glReadPixels).