CNA-BUG-105: SDL_RENDERER clips to any non-empty ScissorRectangle even when RasterizerState.ScissorTestEnable is false

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

SdlRenderer::SetScissorRect installs SDL_SetRenderClipRect for every non-empty rectangle and the renderer has no ApplyRasterizerState override, so a game that sets a scissor rectangle but draws with the test disabled is still clipped.

Identifier

CNA-BUG-105

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.ScissorRectangle together with RasterizerState.ScissorTestEnable on SDL_RENDERER

Expected behaviour

XNA clips only while RasterizerState.ScissorTestEnable is true; the rectangle may stay set while other draws run unclipped (a common UI pattern).

Actual behaviour at TARGET

SdlRenderer.cpp's SetScissorRect calls SDL_SetRenderClipRect(renderer, &rect) for any rectangle with positive size and clears the clip only for an empty one; the scissor-enable flag arrives through ApplyRasterizerState, which SDL_RENDERER does not override (the interface default ignores it). So the clip follows the rectangle, not the test: disabled-test draws are clipped, and an enabled zero-area rectangle removes clipping entirely.

Source locations

• modules/renderers/sdl-renderer/src/SdlRenderer.cpp — SdlRenderer::SetScissorRect
• modules/renderers/sdl-renderer/include/CNA/Internal/Renderers/SdlRenderer/SdlRenderer.hpp — no ApplyRasterizerState override
• modules/graphics/src/Xna/GraphicsDevice.cpp — GraphicsDevice::setScissorRectangleProperty forwards every rectangle

Evidence

Checked by reading the named sources at 009d40f5; nothing was built or executed for this entry.

Focused reproduction

// Illustrative; not compiled or run for this entry.
device.setScissorRectangleProperty(Rectangle(0, 0, 100, 100));
batch.Begin(SpriteSortMode::Deferred, BlendState::AlphaBlend, nullptr, nullptr,
            RasterizerState::CullCounterClockwise);   // ScissorTestEnable = false
batch.Draw(background, Rectangle(0, 0, 800, 600), Color::White);
batch.End();
// XNA: full background.  SDL_RENDERER: only the 100x100 corner is drawn.

Current tests

sdlrenderer_rasterizer_depthstencil_construction_test.cpp checks state construction only; no SDL_RENDERER pixel test toggles ScissorTestEnable.

Regression test

A pixel fixture that sets a small ScissorRectangle and draws full-screen with the test disabled and then enabled, asserting unclipped and clipped results.

Blast radius

UI and HUD code on SDL_RENDERER that leaves a scissor rectangle set between clipped and unclipped passes.

Workaround

Reset ScissorRectangle to the full viewport before unclipped draws.