CNA-BUG-134: Inside a letterbox bar, Mouse::GetState reports the raw window coordinate on renderers whose transform declines the point

CNA snapshot c1c316b9  ·  Known Issues › Current bugs  ·  source links pinned to c1c316b9

EasyGL (every GL-family identity), SDL_GPU and WEBGPU decline points outside the presented rectangle, and Mouse and the input bridge then report the untransformed window coordinate, which can look like a valid game position. The presented rectangle is smaller than the window only under CnaPresentationMode::Letterbox (the default mode) when the window aspect differs from the back buffer's; Overscan, Stretch, NativeBackBuffer and FixedHeightDynamicWidth present a rectangle that covers the whole window, so only a pointer outside the window itself is declined there.

Identifier

CNA-BUG-134

Category

Bug

Subsystem

Input

Status

Open

Verified against

CNA c1c316b9 (c1c316b9c7a846ce8002809c151fcd1af14942c9)

Severity

Low (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

Mouse::GetState() and touch positions under a letterboxed or overscanned presentation

Expected behaviour

A mouse position should always be in one coordinate space. Vulkan returns the logical coordinate even outside the presented rectangle (negative or beyond the back buffer), so a game can tell the pointer is in a bar.

Actual behaviour at TARGET

WindowToLogical in GlPresentationSurfaceState.hpp (EasyGL) computes the logical coordinates and then returns windowX >= clientViewportX && ..., i.e. false inside a Letterbox bar; SDL_GPU and WebGPU do the same. On false, window_to_logical in Mouse.cpp leaves the output at the raw window coordinate, and to_logical_position in SdlInputBridge.cpp returns it too. With a 100-pixel left bar, a pointer at window x = 50 is reported as game x = 50, inside the playfield. Under Overscan the presented rectangle extends past every window edge, so in-window points always map.

Source locations

• modules/renderers/easygl/include/CNA/Internal/Renderers/EasyGL/GlPresentationSurfaceState.hpp — WindowToLogical: returns false outside the viewport
• modules/input/src/Xna/Mouse.cpp — window_to_logical keeps the raw coordinate on false
• modules/input/src/Internal/SdlInputBridge.cpp — to_logical_position returns the raw coordinate on false
• modules/renderers/vulkan/src/VulkanRenderer.cpp — TransformWindowToLogical returns true with out-of-range logical coordinates, for contrast

Evidence

Checked by reading every renderer's TransformWindowToLogical at c1c316b9; not executed.

Independent re-verification: Read every TransformWindowToLogical override and every RegisterForWindow call at c1c316b9; not executed. DIRECTX11 and METAL also decline outside the rectangle but never register for their window (CNA-BUG-133), so input never consults them; VULKAN, FNA3D and the SDL renderer return true without a range check; DIRECTX9's transform (added by FULLSCREEN-002) has no range check either, but DIRECTX9 never registers (CNA-BUG-133).

Focused reproduction

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

Current tests

MouseInputTests.cpp tests the transform inside the presented rectangle only (CoordinateTransformPreservesLetterboxOffsetAndInverse).

Regression test

A test renderer that declines points in a bar, asserting that Mouse::GetState reports an out-of-range logical coordinate (or a documented clamp), never the raw one.

Blast radius

Letterboxed or overscanned windows on the renderers named (every EasyGL identity, SDL_GPU and WEBGPU); clicks in the bars land on game coordinates.

Workaround

Ignore mouse input while the window aspect differs from the back buffer, or compute the bars in the game.