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Compact Machines Preview Fix

Standalone NeoForge 1.21.1 client-side mod that patches the severe memory leak introduced by Compact Machines' room preview (issues CompactMods/CompactMachines#664, FTBTeam/FTB-Modpack-Issues#11675).

Repo: https://github.com/breakinblocks/CompactMachinesPreviewFix

What it does

Compact Machines uses the Gander library to render a 3D preview of the inside of a room. Each preview open leaks in two places:

Per-chunk-section geometry (off-heap RAM)

  • 2 × SectionBufferBuilderPack — pre-sized ByteBufferBuilders (~10–20 MB each)
  • 1 × VertexBuffer per RenderType — OpenGL buffer handle + native staging

Per-preview screen pipeline (VRAM)

SpatialRenderer.state caches a PipelineState containing:

  • RENDER_TARGET — a full-window TextureTarget (color + depth)
  • TRANSLUCENCY_CHAIN — owns a layered texture-array TranslucentRenderTarget and a separate intermediaryCopyTarget FBO that close() does not destroy
  • RENDER_TYPE_STORE — cached RenderType remap maps

Neither BakedLevel/BakedLevelSection nor the SpatialRenderer.state graph is disposed by Gander, and MachineRoomScreen drops the renderer without notice. A 45-cubed room (~27 sections) at 2560×1440 leaks several hundred MB of off-heap RAM plus tens of MB of VRAM per preview open. JVM heap stays small (everything is off-heap / GL), which is why heap profilers look fine while committed RAM balloons until the JVM OOM-crashes — and once VRAM fills the next render aborts with GL_FRAMEBUFFER_INCOMPLETE_ATTACHMENT from TranslucentRenderTarget.

This mod injects into MachineRoomScreen via Mixin to:

  1. Walk the prior SpatialRenderer (its BakedLevel geometry and its cached PipelineState) and release every closeable GPU/native handle before updateScene replaces the renderer.
  2. Do the same cleanup before onClose runs.

All close() / destroyBuffers() calls are routed onto the render thread via RenderSystem.recordRenderCall.

Compatibility

  • Minecraft 1.21.1
  • NeoForge 21.1.55+
  • Compact Machines (any 21.1.x build that still uses Gander's BakedLevel record)

License

MIT.