Simulation

BLine-GUI includes a built-in simulation that previews how your robot will follow the current path. Use it for quick structural checks — does the path flow in the order you expect, do constraints land where you meant them to — before pushing to hardware.

Transport controls

The simulation controls sit at the bottom-left of the canvas:

Control	Function
▶ / ⏸	Play / pause simulation (Space on the canvas).
Timeline slider	Scrub to any point in the path.
Time display	Current time / total duration in seconds.

Scrubbing the timeline while paused is the fastest way to inspect exactly where on the path something happens (a handoff, a rotation target, an event trigger).

What the simulation shows

• Simulated robot footprint — rendered from the configured Robot Length / Robot Width in project config, rotating to match the simulated heading.
• Trajectory trail — orange trail along the path the sim actually walked.
• Rotation evolution — the footprint rotates according to profiled/non-profiled rotation targets.
• Constraint effects — ranged velocity caps visibly slow the footprint through their ordinal ranges.
• Event-trigger fires — the sim visually reacts to show_on_event_keys / hide_on_event_keys for protrusions.
• Protrusion footprint — if protrusions are enabled, the simulated robot footprint changes size as protrusions toggle, not just the dashed overlay.

What the simulation does not show

Limitations

The simulation uses simplified kinematics — it is not a drivetrain physics simulator.

• No PID dynamics. The sim doesn't run the three PID controllers; it uses a simplified v = √(2·a·d) profile to step along the path. Real-robot timing and behavior will differ, especially near path endpoints.
• Perfect traction. No wheel slip, no battery sag, no motor limits.
• No disturbances. Nothing pushes the robot; it just follows the plan.
• Instant acceleration response. No motor time constants, no voltage saturation.

The sim's total path duration is a rough estimate, not a precise prediction. Treat it like a wireframe preview.

For accurate dynamics, use a WPILib physics simulation with your drive code, or test on hardware.

How to use it effectively

Structural validation

Use the sim to confirm path structure is correct before real-robot testing:

• Do the segments connect where you expected?
• Are rotations happening at the right points in the path?
• Do constraint ranges cover the right ordinals? (Click a constraint segment — the canvas overlay confirms.)
• Do event triggers fire in the right order?

Constraint sanity check

Play the sim while adjusting ranged velocity constraints. The simulated footprint visibly decelerates through capped ranges — if the slowdown happens in the wrong place, you've indexed the wrong ordinals.

Identifying design smells

Things to watch for in sim:

• Robot deceleration lingers mid-segment — your velocity constraint range is too wide, or you want handoff radii instead.
• Robot cuts a corner visibly — handoff radii too large, or you need an extra TranslationTarget.
• Rotation finishes too late (near the end of the segment) — reduce the RotationTarget's t_ratio.
• The sim footprint doesn't match the robot's bumper/intake geometry — update Robot Length/Width or enable protrusions in Settings → Edit Config….

Keyboard shortcuts

Shortcut	Action
Space (canvas focus)	Play / pause simulation
Drag timeline slider	Scrub

Next

• Canvas — reading the canvas during sim.
• Protrusions — how the simulated footprint grows/shrinks with event triggers.
• Tuning & Usage Tips — turning sim intuition into real-robot tuning.