An unreal-plugin that lets the user sample scene-cubemaps on the CPU. Made specifically for virtual video production in combination with DMX lights, but can be used for other things as well.
- Only tested in Unreal 5.4.
- WARNING: Might only work in PIE.
This plugin is only reading the "ambient light" (color) from the surrounding scene. It does not consider light coming directly from a lightsource. That's why this plugin might work extra well in combination with: https://github.com/zurra/LXR-Free
Install the plugin like any other: https://dev.epicgames.com/documentation/en-us/unreal-engine/plugins-in-unreal-engine
- Place a
SceneLuminanceCaptureComponentat the location you wish to sample. - Set "Texture Target" to a
CubeRenderTarget, for example T_LuminanceRenderTarget - To sample the scene, use
GetLuminance()inSceneLuminanceCaptureComponent - Press play!
Place the BP_LuminanceSampleTest-pawn in your scene.
When entering play-mode, a debug-widget will be added to the screen:
- Top left - The blurred luminance-values in all directions relative to the camera
- Bottom left - The scene-capture and a red dot representing the uv-coordinate of the current camera direciton.
The scene is rendered to a CubeRenderTarget. This TextureCube only exists on the GPU and has to be copied to the CPU in order for us to read it. A TextureCube has 6 textures, one for each side of the cube. Each texture is coped in a TArray<FLinearColor> using FRenderTarget::ReadLinearColorPixels().
The tricky part is mapping the sample direction (in 3D) to the correct cube face and face UV. My solution was inspired by this, but in reverse: https://stackoverflow.com/a/34427087
- Copying the pixels to CPU should not be done on the game thread, but I found no other way that was thread-safe.
- Investigate the math behind luminance and ambient lighting further.