60 lines
2.8 KiB
Markdown
60 lines
2.8 KiB
Markdown
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# on-demand-rendering Specification
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## Purpose
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Schedules window repaints for the Game of Life canvas: frames are produced only when displayed content changes, and only the changed cells are drawn, so idle CPU usage is near zero while the visible output stays identical to a full repaint.
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## Requirements
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### Requirement: Frame is rendered only on content change
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The system SHALL produce a new rendered frame only when displayed content has changed since the last rendered frame, and SHALL NOT redraw when it has not.
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#### Scenario: Idle while paused
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- **WHEN** the simulation is paused, no tool is active, and no input arrives
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- **THEN** no new frame is rendered over consecutive display refreshes
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#### Scenario: Tick changes grid
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- **WHEN** a simulation tick changes the grid while the simulation is running
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- **THEN** a new frame is rendered that reflects the new generation
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#### Scenario: Edit marks content dirty
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- **WHEN** the user paints cells or places a pattern
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- **THEN** a new frame is rendered with the modified cells
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#### Scenario: Preview follows pointer
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- **WHEN** a tool is selected and the pointer moves to a different cell
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- **THEN** a new frame is rendered with the pattern preview at the new position
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#### Scenario: Preview-affecting action
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- **WHEN** the user selects a tool, rotates the active tool, or toggles grid lines
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- **THEN** a new frame is rendered reflecting the change
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#### Scenario: Resize forces full redraw
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- **WHEN** the canvas size or scale changes
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- **THEN** a new frame is rendered over the whole canvas
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### Requirement: Simulation advances independently of rendering
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The system SHALL accumulate simulation time and apply ticks based on elapsed time, regardless of whether frames are rendered.
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#### Scenario: Ticks accumulate while idle
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- **WHEN** multiple tick intervals elapse without a rendered frame
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- **THEN** every elapsed interval results in exactly one applied tick
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### Requirement: Only changed cells are repainted
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The system SHALL redraw only the cells whose state differs from the last rendered frame, drawing each changed cell's background, grid-line fragments, and cell state, and SHALL leave unchanged cells' pixels untouched.
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#### Scenario: Single cell changes
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- **WHEN** exactly one cell changes state between rendered frames
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- **THEN** only that cell's pixel area is rewritten in the framebuffer
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#### Scenario: Unchanged pixels are preserved
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- **WHEN** a frame is rendered after a change
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- **THEN** pixels of unchanged cells are identical to the previous frame
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### Requirement: Damage is limited to the changed region
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The system SHALL report surface damage covering only the area repainted in the current frame.
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#### Scenario: Small change damages small region
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- **WHEN** only a few cells changed
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- **THEN** the reported damage is limited to the union of those cells' areas rather than the whole surface
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