Backbuffers

A backbuffer is the in-memory drawing surface Gondwana renders into before anything is presented to the screen.

The engine supports two main backbuffer types:

• BitmapBackbuffer
• GpuBackbuffer

Both inherit from BackbufferBase, so the higher-level render pipeline can stay mostly the same.

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BitmapBackbuffer

This is the classic CPU-rendered path.

It uses an in-memory SKBitmap + SKSurface, supports deferred resize requests, and is designed around dirty-rectangle rendering and safe snapshotting for UI presentation.

This is the backbuffer that benefits from Gondwana’s dirty-region system.

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GpuBackbuffer

This is the GL-thread-rendered path.

Instead of rendering on the engine’s normal foreground loop and then copying to the adapter, GPU surfaces render directly on the GL thread into a GPU render target. The engine treats these differently because partial dirty-rectangle presentation is not the main optimization there.

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Shared responsibilities

A backbuffer is responsible for:

• exposing an SKCanvas
• beginning and ending a frame
• drawing tiles and drawables
• tracking dirty screen pixels
• snapshotting rendered output
• resizing when needed

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Mental model

The backbuffer is not the window. It is the engine’s working canvas.

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Where to read next

• Gondwana/Rendering/Backbuffers/BackbufferBase.cs
• Gondwana/Rendering/Backbuffers/BitmapBackbuffer.cs
• Gondwana/Rendering/Backbuffers/GpuBackbuffer.cs