Tutorials · Physics and Mechanisms · Chapter 5

Crates

Four layers

1. Choose File → Project settings… and open its Physics tab. Under Layer names it says that no layer has a name yet. Click Show all layers.
2. Type World into the box of layer 0, Knight into 1, Crate into 2 and Grate into 3, pressing Enter after each.
3. Under Collision matrix, find the row Grate and, in it, the column Knight. Untick that box; every other box stays ticked. Close the window.

Layer names

The Physics tab’s Layer names: a name for each collision layer the project uses, by its number. Every layer row in the Inspector shows these names from now on, and a layer joins the matrix below once it has one. A name is only a name: a scene keeps which layers are ticked, not the words, so renaming a layer changes nothing that collides.

Collision matrix

The Physics tab’s Collision matrix: one box for each pair of named layers. Ticked, a body on one of the two meets a Collider on the other; unticked, they pass through each other. Every box comes ticked. Knight with Grate unticked: the knight walks through the grate, and a crate, on Crate, whose box with Grate is ticked, does not. Areas look through it too: the plate, on World, notices the knight and the crates because World’s boxes with Knight and with Crate are ticked.

1. Select knight. At the foot of his Character Body’s rows, click the button beside Layer, which reads World. Untick World and tick Knight, and click away from the list.

Layer

The Character Body’s Layer, at the foot of its rows: the layers the body is on, what it collides as. Moving, it meets each Collider whose layer has a ticked box with one of its own in the matrix, unless that Collider’s Include or Exclude Layers say otherwise. The knight’s is Knight; a new body’s is World. His Area’s Layer is another field, what a plate looks for; he needs both on Knight, and each is set on its own.

Three crates

1. Select storeroom, click + Add node and choose Sprite. Rename it crate_1 and set its Position to 460, 1568, between the plate and the scaffolding.
2. In its Sprite, drag art/crate.png from Assets onto Texture, and set Size to 24, 24, Anchor to 0.5, 1 and Sort Layer to 2: hung from its feet, on the floor.
3. Click Add component and choose CharacterBodyComponent. Set its Size to 24, 24 and Driven By to Script. In its Pushing fold, tick Pushable and set Push Speed to 0.75. At the foot of its rows, click the button beside Layer, untick World and tick Crate.
4. Click Add component and choose ColliderComponent. Set its Size to 24, 24 and Offset to 0, -12: the crate’s box, standing on its feet. Solid stays ticked. Click the button beside its Layer, untick World and tick Crate.
5. Click Add component and choose AreaComponent. Open its Shape and set Size to 24, 24 and Offset to 0, -12. Click the button beside the Area’s own Layer, untick World and tick Crate. Click the one beside Mask and untick World, so that it reads Nothing.
6. In the Hierarchy, right-click crate_1 and choose Duplicate. Rename the copy crate_2 and set its Position to 157, 1568, on the floor west of the doorway. Duplicate it again: crate_3, at 224, 1448. It hangs in the air until the shelf is built under it, below.

Driven By

The Character Body’s Driven By: who sets the body’s own velocity. Keys, as the knight’s, walks it with A and D and jumps it with Space; Script leaves it to a script. A crate is Script with no script, so nothing ever walks it: the keys never do, and only a shove, gravity and what the shove leaves it move it. Left at Keys, it would walk beside him. A new body’s is Keys.

Pushable

The Character Body’s Pushable, in its Pushing fold: ticked, a body that walks into this one shoves it along, instead of stopping. It needs a solid Collider of its own to be walked into, as each crate has. A new body’s is unticked: the knight is not pushable.

Push Speed

The Character Body’s Push Speed: how much of the pusher’s walk a shove gives this body, from 0 to 1. At 1 it keeps pace with him; at 0.5, as a new body comes, it goes at half his speed, and he with it. The crates’ 0.75 takes his walk of 160 a second to 120 while he shoves: he is slowed as by a weight, not stopped.

Layer

The Collider’s Layer: the layers it is on, what it is to everything that meets it, looks for it or casts at it. A crate’s Collider is on Crate, as its body is: its body is what moves it and what it collides as, its Collider what the knight walks into and what another crate lands on. A new Collider is on World, as the tower’s stone is.

A grate he walks through

1. Select storeroom and add a Sprite named grate: Position 248, 1568; Texture grate.png, Size 16, 40, Anchor 0.5, 1, Sort Layer 1.
2. Click Add component and choose ColliderComponent: Size 16, 40, Offset 0, -20. Click the button beside its Layer, untick World and tick Grate.
3. Select grate, click + Add node and choose Node. Rename it grate_rail and set its Position to 0, -40.
4. Click Add component and choose ColliderComponent: Size 16, 3, Offset 0, 1.5. Click the button beside its Layer, untick World and tick Grate, like the grate. Click the button beside Include Layers and tick Knight.

Include Layers

The Collider’s Include Layers: layers that meet this Collider whatever the matrix says. A body on one of them stands on it and is stopped by it. It does not put the Collider on them: the rail stays on Grate, a part of the grate to everything else. So the knight, whom the matrix passes through Grate, stands on the rail and still walks under it, through the bars. A new Collider’s is Nothing.

A shelf, a chute and a pillar

1. Select storeroom and add a Sprite named shelf: Position 232, 1452; Texture scaffold-plank.png, Size 48, 8, Draw Mode Tiled and Tile Size 48, 8. Add a ColliderComponent: Size 48, 8, and tick One Way.
2. Add another Sprite under storeroom, named chute: Position 192, 1452; Texture scaffold-plank.png, Size 32, 8, Draw Mode Tiled and Tile Size 48, 8. Add a ColliderComponent: Size 32, 8. Its Layer stays World. Click the button beside Exclude Layers and tick Crate.
3. Add a third, storeroom_pillar: Position 32, 1572; Texture old-dark-castle-interior-tileset.png with Atlas Region pillar, Size 32, 144, Anchor 0.5, 1, Sort Layer -1, Draw Mode Tiled and Tile Size 32, 72: the tileset’s pillar twice, one on the other. Add a ColliderComponent: Size 32, 144, Offset 0, -72.

Exclude Layers

The Collider’s Exclude Layers: layers that pass through this Collider whatever the matrix says. It does not take the Collider off its own Layer: the chute stays on World, so the knight stands on it, and a crate, on Crate, falls through it. Include and Exclude Layers count from either of two Colliders that meet, and where one includes a layer and the other excludes it, the exclude wins: they pass. A new Collider’s is Nothing.

The plate looks for crates

1. Select plate. Click the button beside its Area’s Mask, which reads Knight, and tick Crate as well: it reads Knight, Crate. Press Ctrl+S.

Shoving

1. If you take chapter 4’s skip: with the game stopped, select knight and set his Position to 560, 1568, on the scaffolding’s top plank.
2. Select knight, so that the Inspector shows his Character Body while the game runs, and press F5.
3. Walk him up the scaffolding into the storeroom, and hold A: he walks into crate_1 and shoves it west, slower than he walks. In the Inspector, Shoving is ticked on every step he shoves.
4. Let go of A as the crate reaches the plate. The portcullis rises, and stays up with him off the plate.

Shoving

The Character Body’s Shoving, read live in Play: ticked on a step this body shoved a Pushable body along. It is off when he walks free, and off when what he walks into will not give way: then he is On Wall instead. The body writes it every step, so there is nothing to type.

On Wall

The Character Body’s On Wall, read live, as in chapter 2: ticked on a step his walk was stopped sideways. A crate that cannot move, against the grate or the pillar, stops him as a wall does, and he is On Wall, not Shoving.

The way up

1. With the crate on the plate, hop over it: tap Space with A held. Walk on west, under the raised portcullis and through the grate.

1. From the floor just west of the grate, jump back east onto its rail: hold D, press Space, and let go of D as he comes over it. From the rail, jump up through the shelf onto it.
2. On the shelf, walk west into crate_3, and keep walking: it goes off the shelf’s west end, falls through the chute onto crate_2, and stands on it. Walk on onto the chute and stop there.

1. Walk back east onto the shelf and drop through it: S with Space. He lands on the floor east of the stack.
2. Hold A: he shoves the stack west, the top crate riding the bottom one, until the pillar stops it.
3. Jump onto the stack. From it, jump onto the pillar, holding A. From the pillar, jump with D held, up through the opening onto the ice hall’s floor.
4. Press F5 to stop. If you took the skip, select knight and set his Position back to 48, 1792, his start.

The layers, the crates and the grate

Check it works