## ADDED Requirements

### Requirement: Ground grid is rendered in the viewport

The system SHALL render a ground plane grid at the Y=0 plane (XZ plane) to provide spatial reference.

#### Scenario: Grid visible by default
- **WHEN** the viewport is displaying a scene
- **THEN** a grid is drawn on the Y=0 plane with lines at regular intervals

#### Scenario: Grid can be toggled off
- **WHEN** the user toggles the grid display off via the viewport context menu
- **THEN** the grid is no longer rendered

### Requirement: Axis gizmo is rendered in the viewport corner

The system SHALL render a 3D axis indicator (RGB for XYZ) in the lower-left corner of the viewport to show scene orientation.

#### Scenario: Axis gizmo visible
- **WHEN** the viewport is displaying a scene
- **THEN** an axis gizmo is drawn in the lower-left corner with X=red, Y=green, Z=blue lines and labels

#### Scenario: Axis gizmo reflects camera orientation
- **WHEN** the camera is rotated
- **THEN** the axis gizmo orientation updates to reflect the current view direction

### Requirement: Viewport background color is configurable

The system SHALL render the viewport background with a configurable color, defaulting to a dark gray (0.15, 0.15, 0.15).

#### Scenario: Default background color
- **WHEN** the viewport is rendered
- **THEN** the background is cleared to dark gray (0.15, 0.15, 0.15)

#### Scenario: Background color changed via context menu
- **WHEN** the user selects a different background color from the viewport settings
- **THEN** the viewport background is updated to the selected color

### Requirement: Viewport context menu provides display options

The system SHALL provide a right-click context menu in the viewport with toggles for grid display and background color options.

#### Scenario: Right-click opens context menu
- **WHEN** the user right-clicks within the viewport area
- **THEN** a context menu appears with options: "Show Grid" (toggle), and "Background" submenu with color presets

#### Scenario: Toggle grid from context menu
- **WHEN** the user clicks "Show Grid" in the context menu
- **THEN** the grid display is toggled on or off