# cell-grid Specification

## Purpose
Stores and renders the Game of Life cell grid with a fixed cell size and wall boundaries, independent of future simulation rules.

## Requirements

### Requirement: Grid stores alive and dead cells
The system SHALL maintain a grid of cells, each either alive or dead, addressable by column and row.

#### Scenario: Cell access
- **WHEN** a cell is set to alive
- **THEN** reading that cell returns alive
- **AND** cells never set remain dead

### Requirement: Boundary cells are treated as dead
The system SHALL treat any cell outside the grid bounds as dead and shall not store state outside the grid.

#### Scenario: Out of bounds read
- **WHEN** a cell position outside the grid is queried
- **THEN** the result is dead

### Requirement: Grid resizes while preserving overlapping cells
The system SHALL preserve cells that remain within bounds when the grid dimensions change, clearing only cells that fall outside the new bounds.

#### Scenario: Enlarge grid
- **WHEN** the grid grows in either dimension
- **THEN** previously alive cells within the old bounds remain alive

#### Scenario: Shrink grid
- **WHEN** the grid shrinks in either dimension
- **THEN** cells outside the new bounds are discarded
- **AND** remaining cells keep their state

### Requirement: Cell size is fixed in logical pixels
The system SHALL use a cell size of 8 logical pixels, so grid dimensions derive from the logical surface size.

#### Scenario: Dimension calculation
- **WHEN** the logical surface is 400 pixels wide
- **THEN** the grid has 50 columns

### Requirement: Alive cells are rendered
The system SHALL render alive cells distinctly from dead cells.

#### Scenario: Render alive cell
- **WHEN** a cell is alive
- **THEN** it is drawn with the alive cell color

### Requirement: Grid can be cleared
The system SHALL set all cells to dead when the clear action is triggered.

#### Scenario: Clear grid
- **WHEN** the user triggers the clear action
- **THEN** all cells become dead

### Requirement: Grid lines can be toggled
The system SHALL show or hide grid lines when the toggle_grid action is triggered.

#### Scenario: Toggle lines
- **WHEN** the user triggers the toggle_grid action
- **THEN** grid line visibility flips