Make Canvas immediate-mode (per-frame vertex buffer) #13

New Issue

2026-09-25T20:36:45-07:00

burkkyy commented

2026-09-25 20:36:45 -07:00

Canvas is meant to be an immediate-mode drawing API (debug draw, gizmos, prototypes, examples), but it currently behaves as a retained one.

Problem

Each Canvas::triangle / Canvas::quad call goes through Application::pushMesh, which creates a new GPU Mesh that lives until Canvas::clear(). clear() calls device.waitIdle() before freeing them.

Calling Canvas from onUpdate every frame creates GPU buffers without limit.
Drawing once in onCreate only works by accident.

Proposal

Canvas calls append vertices/indices to a per-frame CPU array.
Each frame, that array is uploaded into a dynamic vertex/index buffer (one per frame in flight), drawn, then reset automatically.
Remove Canvas::clear(), the waitIdle in clearMeshes, and the meshes list in Application::Impl.
Decide what Canvas draws into: the main backbuffer, on top of everything, to start with. Later possibly a chosen scene view, e.g. editor viewport overlays.
Application::camera (Camera2D) only exists for Canvas. Move it onto Canvas, or make Canvas draw in screen space, so it isn't confused with scene cameras.

Done when

examples/triangle works with drawing done in onUpdate each frame
GPU memory stays flat when Canvas is used every frame
No waitIdle on the Canvas path

Canvas is meant to be an immediate-mode drawing API (debug draw, gizmos, prototypes, examples), but it currently behaves as a retained one. ## Problem Each `Canvas::triangle` / `Canvas::quad` call goes through `Application::pushMesh`, which creates a new GPU `Mesh` that lives until `Canvas::clear()`. `clear()` calls `device.waitIdle()` before freeing them. - Calling Canvas from `onUpdate` every frame creates GPU buffers without limit. - Drawing once in `onCreate` only works by accident. ## Proposal - Canvas calls append vertices/indices to a per-frame CPU array. - Each frame, that array is uploaded into a dynamic vertex/index buffer (one per frame in flight), drawn, then reset automatically. - Remove `Canvas::clear()`, the `waitIdle` in `clearMeshes`, and the `meshes` list in `Application::Impl`. - Decide what Canvas draws into: the main backbuffer, on top of everything, to start with. Later possibly a chosen scene view, e.g. editor viewport overlays. - `Application::camera` (`Camera2D`) only exists for Canvas. Move it onto Canvas, or make Canvas draw in screen space, so it isn't confused with scene cameras. ## Done when - `examples/triangle` works with drawing done in `onUpdate` each frame - GPU memory stays flat when Canvas is used every frame - No `waitIdle` on the Canvas path

burkkyy added the enhancement label 2026-09-25 20:36:45 -07:00

burkkyy added this to the sophia project 2026-09-25 20:37:46 -07:00

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Reference: burkkyy/sophia#13