CNA-GAP-014: CANVAS and FREEDIRECT ignore GraphicsDevice.Viewport and ScissorRectangle, and SDL_RENDERER ignores Viewport

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

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Evidence basis: source-verified at the pinned commit; tests exist (not executed for this page). Claims on this page were checked by reading the CNA source at commit 009d40f5; unless a sentence says otherwise, nothing here was built or executed. Nothing on this page was executed unless the Evidence section says so.

The renderers leave the no-op IGraphicsRenderer::SetViewport (and, on CANVAS and FREEDIRECT, SetScissorRect) in place, so a custom viewport never offsets drawing and a scissor rectangle never clips there.

Identifier: CNA-GAP-014
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: GraphicsDevice.Viewport and GraphicsDevice.ScissorRectangle (with RasterizerState.ScissorTestEnable) on CANVAS, FREEDIRECT and SDL_RENDERER

Expected behaviour

XNA SpriteBatch and 3D drawing honour the device viewport, and an enabled scissor rectangle clips rasterisation - split-screen and UI clipping depend on both.

Actual behaviour at TARGET

IGraphicsRenderer::SetViewport and SetScissorRect are empty defaults in IGraphicsRenderer.hpp. CANVAS (CanvasRenderer.cpp) and FREEDIRECT (FreeDirectRenderer.cpp) override neither, and SDL_RENDERER (SdlRenderer.cpp) overrides only SetScissorRect. GraphicsDevice validates and stores the values, so the getters round-trip while nothing changes on screen. SDL_RENDERER also has no applied-format override, so PresentationParameters keeps the requested depth format (for example Depth24) on a renderer without a depth buffer. The SDL_RENDERER scissor-enable defect is published separately as CNA-BUG-105.

Source locations

modules/graphics/include/CNA/Internal/Renderers/Common/IGraphicsRenderer.hpp — SetViewport and SetScissorRect no-op defaults
modules/renderers/canvas/src/CanvasRenderer.cpp — no SetViewport/SetScissorRect override
modules/renderers/freedirect/src/FreeDirectRenderer.cpp — no SetViewport/SetScissorRect override
modules/renderers/sdl-renderer/include/CNA/Internal/Renderers/SdlRenderer/SdlRenderer.hpp — overrides SetScissorRect only; no GetApplied*FormatEXT

Evidence

Checked by reading the named sources at 009d40f5; nothing was built or executed for this entry. Established by grepping the three renderers' headers and sources for the overrides.

Focused reproduction

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

Current tests

No viewport or scissor pixel fixture is registered for CANVAS or FREEDIRECT, and none checks a custom viewport on SDL_RENDERER.

Regression test

Register the shared viewport and scissor fixtures for these renderers, or make them refuse the settings explicitly and test the refusal.

Blast radius

Split-screen, letterboxed UI and clipped scroll panels on the three 2D renderers.

Workaround

Offset and clip in game code (render to a render target and draw a sub-rectangle).

The same subject is explained at several altitudes. These are the neighbouring pages at each one.

Deep dives: Viewports per renderer family · SDL_RENDERER: native and emulated behaviour
Known issues: Functional gap index