TerminalImageViewer renders RGBA buffers directly to the terminal for debugging test failures. It is enabled by default for ImageComparisonTestFixture failures and can be adjusted at runtime without recompiling tests.

Usage in tests

• ImageComparisonParams::showTerminalPreview gates whether the fixture emits the 2x2 grid of Actual/Expected/Diff panels.
• The fixture scales each panel to fit the current terminal width while preserving aspect ratios.
• Captions appear above each panel; the bottom-right cell remains empty to keep alignment stable.

Environment controls

• DONNER_ENABLE_TERMINAL_IMAGES (default: 1): set to 0 to disable previews in all tests.
• DONNER_TERMINAL_PIXEL_MODE: override sampling granularity. Accepts quarter (default) or half.
• COLUMNS: overrides the detected terminal width when scaling panels.

When running inside a VS Code interactive terminal, the renderer automatically enables VS Code line endings and truecolor output. Capability detection can also be overridden by passing TerminalImageViewerConfig directly to the renderer in custom harnesses.