CNA-BUG-116: DIRECTX9 never resolves multisampled render targets bound as a multiple-render-target set

CNA snapshot 009d40f5  ·  Known Issues › Current bugs  ·  source links pinned to 009d40f5

SetRenderTargets binds each MSAA target's multisample surface but does not track an MRT set, so when the set is unbound no StretchRect resolve runs and the textures keep stale contents.

Identifier

CNA-BUG-116

Category

Bug

Subsystem

Graphics & renderers

Status

Open

Verified against

CNA 009d40f5 (009d40f5dd085c4e674d3479675fac84b12b3e0a)

Severity

Medium (a triage suggestion, not a project priority)

Evidence basis

Source-verified: read at TARGET, not executed

Tests touching this area

Yes: see Current tests

Affected contract

GraphicsDevice::SetRenderTargets with two or more multisampled RenderTarget2D bindings on DIRECTX9

Expected behaviour

After a multisampled render target is unbound, sampling it or reading it with GetData must see the resolved result of the draws (DIRECTX9 does this for a single target through ResolveForTransitionEXT).

Actual behaviour at TARGET

DirectX9Renderer.cpp's MRT branch of SetRenderTargets binds GetActiveColorSurfaceEXT() for each target - the multisample surface when MSAA is applied (D3D9RenderTargets.hpp) - then sets currentCustomRT_ = nullptr, with the comment "MRT binds are NOT tracked". The next transition resolves only currentCustomRT_, which is null, so none of the MRT members is StretchRect-resolved into its texture.

Source locations

• modules/renderers/directx9/src/DirectX9Renderer.cpp — DirectX9Renderer::SetRenderTargets MRT branch and SetRenderTarget2D resolve
• modules/renderers/directx9/include/CNA/Internal/Renderers/DirectX9/D3D9RenderTargets.hpp — GetActiveColorSurfaceEXT returns msaaSurface_ when MSAA is applied
• modules/renderers/directx9/src/D3D9RenderTargets.cpp — D3D9RenderTargetRenderer::ResolveForTransitionEXT

Evidence

Checked by reading the named sources at 009d40f5; nothing was built or executed for this entry. Whether a device grants MSAA on all MRT members depends on D3D9 caps.

Focused reproduction

No focused reproduction is known. Nothing has been invented here; the evidence above is what exists.

Current tests

No DIRECTX9 fixture combines MRT and multisampling.

Regression test

An MRT+MSAA fixture on DIRECTX9: draw distinct colours to two 4x-MSAA targets, unbind, read both back.

Blast radius

Deferred and multi-output techniques with MSAA on DIRECTX9; single MSAA targets and non-MSAA MRT sets are unaffected.

Workaround

Use MultiSampleCount 0 for MRT members on DIRECTX9.