CNA-GAP-011: PresentationParameters.RenderTargetUsage is stored, cloned and exposed but never consulted by GraphicsDevice

CNA snapshot 009d40f5  ·  Known Issues › Functional gaps  ·  source links pinned to 009d40f5

Only a render target's own usage is read (in SetRenderTargets); the back buffer's RenderTargetUsage has no effect when SetRenderTargets returns to the back buffer.

Identifier

CNA-GAP-011

Category

Functional gap

Subsystem

Graphics & renderers

Status

Open

Verified against

CNA 009d40f5 (009d40f5dd085c4e674d3479675fac84b12b3e0a)

Evidence basis

Source-verified: read at TARGET, not executed

Tests touching this area

Yes: see Current tests

Affected contract

Microsoft::Xna::Framework::Graphics::PresentationParameters::RenderTargetUsage

Expected behaviour

XNA exposes PresentationParameters.RenderTargetUsage as the back buffer's contents policy (DiscardContents by default, PreserveContents to keep its pixels across a render-target switch).

Actual behaviour at TARGET

The property is stored and cloned in PresentationParameters.cpp and copied by the C API and the device-information equality code, but the only getRenderTargetUsageProperty() call in GraphicsDevice.cpp reads the first bound render target's usage. Whatever the back buffer's contents are after a switch is decided by each renderer, independent of the requested value.

Source locations

• modules/graphics/src/Xna/PresentationParameters.cpp — renderTargetUsage_ storage
• modules/graphics/src/Xna/GraphicsDevice.cpp — GraphicsDevice::SetRenderTargets (reads only the bound target's usage)

Evidence

Checked by reading the named sources at 009d40f5; nothing was built or executed for this entry. What each renderer actually does with the back buffer across a switch was not surveyed.

Focused reproduction

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

Current tests

No test sets the back buffer's RenderTargetUsage and checks its contents after a render-target pass.

Regression test

A fixture that draws to the back buffer, renders to a target, returns, and checks the earlier pixels with PreserveContents (kept) and DiscardContents (XNA's documented discard).

Blast radius

Games that request PreserveContents for the back buffer to keep drawing across render-target passes.

Workaround

Render the scene into your own render target and draw it to the back buffer each frame.