Move the offscreen scene target into the render graph #9

New Issue

2026-09-21T01:31:31-07:00

burkkyy commented

2026-09-21 01:31:31 -07:00

Summary

The swapchain backbuffer is now rendered through RenderGraph (engine/src/rendering/), but the offscreen scene target still does its own layout transitions and beginRendering/endRendering in Application::Impl::run (engine/src/application.cpp). Move the scene target into the graph so every pass in a frame goes through it.

Background

RenderGraph derives barriers and layout transitions from what each pass declares it does to an image (writeColor, sample, use), and begins/ends rendering for passes that write color attachments.
Image::transitionLayout now uses the same Access table (engine/src/rendering/access.hpp), so it no longer throws on unlisted layout pairs.
The scene target block in application.cpp still calls transitionLayout and beginColorPass by hand, and the backbuffer pass has an if (!sceneTarget) branch to decide whether it also draws the scene.
SceneRenderer (engine/src/scene_renderer.hpp) is an empty stub. render() does nothing.
The scene target is being reworked separately, so this should be designed together with that rework rather than bolted on first.

Proposal

Import the target's image into the graph with final access SampledRead. A "scene" pass writes it; the "ui" pass calls sample() on it and writeColor() on the backbuffer.
Replace SceneRenderer::render with addPasses(RenderGraph&, const Scene&, RenderTargetHandle) so the scene renderer registers its own passes.
If there is no target, the scene pass writes the backbuffer instead of application.cpp branching.
Delete beginColorPass and the manual transitionLayout calls in application.cpp.

Open question: ImGui's reads are dynamic

Panels decide which targets they display during panelRegistry.update, so the ui pass's sample() list has to come from that. Options:

The UI reports which targets it displayed this frame, and the graph is built after panelRegistry.update.
The ui pass always samples the scene target.

The first is needed once several panels can show different targets. Note ImGui's descriptor assumes eShaderReadOnlyOptimal, which is what Access::SampledRead maps to.

Out of scope

Transient/aliased resources, pass culling and reordering, and depth attachments in PassBuilder. Revisit once there are more passes.

## Summary The swapchain backbuffer is now rendered through `RenderGraph` (`engine/src/rendering/`), but the offscreen scene target still does its own layout transitions and `beginRendering`/`endRendering` in `Application::Impl::run` (`engine/src/application.cpp`). Move the scene target into the graph so every pass in a frame goes through it. ## Background - `RenderGraph` derives barriers and layout transitions from what each pass declares it does to an image (`writeColor`, `sample`, `use`), and begins/ends rendering for passes that write color attachments. - `Image::transitionLayout` now uses the same `Access` table (`engine/src/rendering/access.hpp`), so it no longer throws on unlisted layout pairs. - The scene target block in `application.cpp` still calls `transitionLayout` and `beginColorPass` by hand, and the backbuffer pass has an `if (!sceneTarget)` branch to decide whether it also draws the scene. - `SceneRenderer` (`engine/src/scene_renderer.hpp`) is an empty stub. `render()` does nothing. - The scene target is being reworked separately, so this should be designed together with that rework rather than bolted on first. ## Proposal - Import the target's image into the graph with final access `SampledRead`. A `"scene"` pass writes it; the `"ui"` pass calls `sample()` on it and `writeColor()` on the backbuffer. - Replace `SceneRenderer::render` with `addPasses(RenderGraph&, const Scene&, RenderTargetHandle)` so the scene renderer registers its own passes. - If there is no target, the scene pass writes the backbuffer instead of `application.cpp` branching. - Delete `beginColorPass` and the manual `transitionLayout` calls in `application.cpp`. ## Open question: ImGui's reads are dynamic Panels decide which targets they display during `panelRegistry.update`, so the ui pass's `sample()` list has to come from that. Options: - The UI reports which targets it displayed this frame, and the graph is built after `panelRegistry.update`. - The ui pass always samples the scene target. The first is needed once several panels can show different targets. Note ImGui's descriptor assumes `eShaderReadOnlyOptimal`, which is what `Access::SampledRead` maps to. ## Out of scope Transient/aliased resources, pass culling and reordering, and depth attachments in `PassBuilder`. Revisit once there are more passes.

burkkyy added the enhancement label 2026-09-21 01:31:31 -07:00

burkkyy added this to the sophia project 2026-09-21 01:38:29 -07:00

burkkyy moved this to Blocked / Discussion in sophia on 2026-09-25 20:43:48 -07:00

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Reference: burkkyy/sophia#9