The Live tab
The Live tab: the running game, as it plays
Section titled “The Live tab: the running game, as it plays”When you press Play (F5), your game runs in its own window. The bottom panel’s Live tab shows that running game from inside the editor: what’s in the scene that’s playing, any node’s values (and you can change them while it runs), how long each frame takes, and buttons to pause the game and step it one frame at a time.
Use it to find out why something misbehaves without adding log lines: is the enemy’s speed what you think? Is the door’s collision shape where it should be? Which part of the frame is slow?
- Opening it
- Pause and step
- Frame times: is the game fast enough?
- The running scene’s nodes
- Changing values while it runs
- How it works
- Questions
Opening it
Section titled “Opening it”- Press Play (F5).
- Open the bottom panel’s Live tab (if the panel is narrow, scroll its tab strip sideways with the mouse wheel to reach it).
It shows “Press Play” while no game runs. Games started from the editor answer it; exported games never do.
Pause and step
Section titled “Pause and step”- Pause (or F6, or the toolbar’s pause button): the game stops updating. It keeps drawing, so you can look at the frozen moment: where everything is, every value.
- Step a Frame (while paused): the game runs exactly one frame (1/60 of a second) and stops again. Step through a jump, a collision, an animation, frame by frame.
- Resume (or F5): it carries on.
The editor’s pause used to stop the game’s program (on Linux and macOS only); with the Live tab the game pauses itself, so it works on every computer.
Frame times: is the game fast enough?
Section titled “Frame times: is the game fast enough?”The line at the top says, averaged over the last half second:
| Number | What it is |
|---|---|
| fps | Frames per second (60 is smooth on most screens) |
| frame | Milliseconds from one frame to the next (16.7 ms at 60 fps) |
| update | How long your game’s logic took: scripts, globals, the scene’s nodes, physics |
| physics | The physics simulation alone (part of update) |
| draw | How long drawing took |
| nodes, drawn | Nodes in the scene, and how many drew something |
Under it, a graph of frame times: one bar per quarter second, the orange line at 16.7 ms. Bars above the line are frames slower than 60 fps: something took too long then.
What to do when it’s slow:
- update high: a script does too much each frame (searching all nodes, finding paths every frame, building strings), or there are very many nodes or bodies.
- physics high: many moving bodies, or many complicated shapes.
- draw high: many things drawn (see drawn), big images scaled, many particles, many lights with shadows.
- frame high but update and draw low: the computer is waiting for the screen (vsync) or busy with something else; nothing to fix in the game.
The running scene’s nodes
Section titled “The running scene’s nodes”The left side lists every node of the scene that’s playing, as the scene tree shows them (children indented under their parents), including nodes your scripts made while it runs (bullets, enemies, particles). Hidden nodes are dimmed. The list updates twice a second.
Click a node to see its values on the right: its position, rotation, scale, tint, opacity,
visibility, z index, what its kind has (a label’s text, a light’s energy…), and its script’s
fields (speed (script)).
Changing values while it runs
Section titled “Changing values while it runs”Type in any value’s field: the game changes at once. Move a platform, make the player faster,
hide something, change a script’s value. Values are written as in the inspector: 120, 300 for a
position, #ff8000 for a color, true or false.
These changes only affect the running game: the project isn’t changed, and they’re gone when the game stops. When you’ve found the right value, set it in the inspector.
A value the game can’t use (“abc” for a speed) is refused: the Console says so.
How it works
Section titled “How it works”Play starts the game with --live. The editor writes commands to the game’s input (watch, select
a node, set a value, pause, resume, step) and the game answers in its output, in lines starting
with @@live that the editor takes out of the Console. See the engine’s live.odin for the
details, if you build your own tools.
Questions
Section titled “Questions”The tab says “Waiting for the game”. The game is still starting (loading its first scene), or it crashed: look in the Console.
A node I changed jumps back. Something in the game sets it every frame (a script, an Animator, physics): your change lasts one frame. Pause first, or change what sets it.
The list is long and slow. Scenes with thousands of nodes send long lists; it doesn’t slow the game much, but finding a node takes scrolling.