CNA-BUG-133: DIRECTX9 implements the window-to-logical transform but never registers for its window, so mouse and touch input ignore it

CNA snapshot 3b43bd86  ·  Known Issues › Current bugs  ·  source links pinned to 3b43bd86

Input looks renderers up by window id through IGraphicsRenderer::GetForWindow; DIRECTX9 never calls RegisterForWindow, so Mouse::GetState, Mouse::SetPosition and touch pass raw window coordinates through under a virtual resolution, letterbox or display scale.

Identifier

CNA-BUG-133

Category

Bug

Subsystem

Input

Status

Open

Verified against

CNA 3b43bd86 (3b43bd8687ed46523d873f9bec4b32bd8481dcb5)

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

Mouse::GetState(), Mouse::SetPosition(int, int) and TouchPanel positions on the DIRECTX9 renderer

Expected behaviour

IGraphicsRenderer.hpp states the registry rule: “Renderers that implement coordinate conversion register themselves here so input can map platform window-client coordinates”. EasyGL, SDL_GPU, WebGPU and FNA3D call RegisterForWindow.

Actual behaviour at TARGET

DirectX9Renderer.cpp implements TransformWindowToLogical and TransformLogicalToWindow (presentation geometry, letterbox, display scale; added by FULLSCREEN-002) but contains no RegisterForWindow call. window_to_logical and logical_to_window in Mouse.cpp and to_logical_position in SdlInputBridge.cpp find no renderer and return the window coordinate unchanged, so a game whose back buffer differs from the window size receives window pixels as game coordinates.

Source locations

• modules/renderers/directx9/src/DirectX9Renderer.cpp — TransformWindowToLogical / TransformLogicalToWindow (added by FULLSCREEN-002); no RegisterForWindow
• modules/graphics/include/CNA/Internal/Renderers/Common/IGraphicsRenderer.hpp — RegisterForWindow / GetForWindow and the registry comment
• modules/input/src/Xna/Mouse.cpp — window_to_logical and logical_to_window fall back to the raw coordinate
• modules/input/src/Internal/SdlInputBridge.cpp — to_logical_position, used for mouse motion and touch

Evidence

Checked by reading and by grepping every renderer source for RegisterForWindow at 3b43bd86; not executed (DIRECTX9 is Windows-only).

Re-verified at c6dec91f: RegisterForWindow is called by EasyGLRenderer.cpp, Fna3dRenderer.cpp, SdlGpuRenderer.cpp and WebGPURenderer.cpp only; DirectX9Renderer.cpp still implements both transforms. Not executed.

Focused reproduction

// Illustrative; not compiled or run. CNA_GRAPHICS_RENDERER=DIRECTX9,
// PreferredBackBuffer 800x480, window resized to 1600x960.
MouseState s = Mouse::GetState();
// Pointer at the window centre: expected (400, 240); actual (800, 480).

Current tests

MouseInputTests.cpp (CoordinateTransformPreservesLetterboxOffsetAndInverse) registers a test renderer by hand; IGraphicsRendererWindowRegistryTests.cpp tests the registry. No test checks that each renderer registers itself.

Regression test

A per-renderer check that constructing the renderer on a window makes GetForWindow(window) return it (the SDL_GPU constructor test already does this); the fix is to register after initialisation and unregister on destruction, as the other renderers do.

Blast radius

Games on DIRECTX9 whose window is not exactly the back-buffer size, including resizable and fullscreen-letterboxed windows: mouse, SetPosition and touch positions are wrong. Other renderers are unaffected.

Workaround

Keep the window at the back-buffer size, or scale mouse coordinates in the game.