UsdLayerManager/openspec/changes/multi-viewport-support/specs/viewport-layout/spec.md

ADDED Requirements

Requirement: Layout presets

The viewport container SHALL support switching between four layout presets at any time: Single (1 tile), HSplit (2 tiles side-by-side), VSplit (2 tiles top-bottom), and Quad (4 tiles in a 2×2 grid).

Scenario: Switch layout from Single to HSplit

• WHEN the user selects "Horizontal Split" from the layout menu
• THEN the viewport splits into two equal-sized tiles side-by-side

Scenario: Switch layout from HSplit to Single

• WHEN the user selects "Single" from the layout menu
• THEN the two tiles merge back into a single tile, and the focused tile's camera/settings are preserved

Scenario: Switch from HSplit to Quad

• WHEN the user switches from HSplit to Quad
• THEN four tiles are created in a 2×2 grid, filling the viewport area

Requirement: Draggable dividers

The divider line between tiles SHALL be draggable to resize adjacent tiles. Dividers SHALL be 6px wide with visual hover feedback.

Scenario: Drag horizontal divider

• WHEN the user clicks and drags the divider between two tiles
• THEN the divider follows the mouse, and tiles resize proportionally

Scenario: Drag divider to edge

• WHEN the user drags a divider to within 10% of the viewport edge
• THEN the divider snaps back to the 10% boundary to prevent tiles from becoming too small (minimum 100px per dimension)

Requirement: Layout applies to the entire viewport area

When the layout changes, all tiles SHALL be redistributed to fill the entire available viewport panel content region. No gaps between tiles.

Scenario: Resize main window with Quad layout

• WHEN the user resizes the main application window
• THEN all four tiles resize proportionally to maintain their relative sizes and fill the viewport content area

Requirement: Space-key maximize restores previous layout

When maximized, pressing Space again SHALL restore the exact layout and divider positions from before maximization.

Scenario: Maximize and restore preserves layout

• WHEN the user has an HSplit layout with divider at 0.3, then hovers tile B and presses Space, then presses Space again
• THEN the viewport returns to HSplit layout with both tiles visible and the divider at 0.3

Requirement: Escape restores maximized viewport

When maximized, pressing Escape SHALL restore the previous layout (same behavior as Space toggle).

Scenario: Escape during maximize

• WHEN the viewport is maximized and the user presses Escape
• THEN the previous multi-tile layout is restored

Requirement: Space requires tile hover in multi-tile layouts

In Single layout (only 1 tile), Space SHALL be a no-op — there is nothing to maximize.

Scenario: Space ignored in Single layout

• WHEN the viewport is already in Single layout and the user presses Space
• THEN the viewport remains unchanged in Single layout