Tutorials · Physics and Mechanisms · Chapter 10

The updraft

Start on this floor

1. Select knight and set his Position to 489, 672. Press F5: he stands on the upper hall’s floor, west of H5, and the hall rises empty over him. Press F5 to stop.
2. Set his Position back to 48, 1792, or press Ctrl+Z until it reads so.
3. Select tower, click + Add node and choose Node. Rename it upper_hall. Every node in this chapter goes under it, but crosswind_streaks, which goes under crosswind.

The loft’s floor

1. Select stone in the Hierarchy and open the Tilemap tab beside the Inspector. Under Layers, click stone.
2. Click Pick, or press I over the Viewport. Drag over the upper hall’s floor, both its rows, from x 96, column 6, to x 544, column 33, the last cell before H5. The bar along the bottom of the window says “Lifted 28x2”.
3. Click Stamp, or press S. The block’s outline follows the pointer, its top left corner at the cell under it; the cursor readout under the Viewport says where that is. Click at x 96, y 448: column 6 of row 28.
4. With Pick again, drag over the same floor from column 6 to column 10, five cells, both rows.
5. With Stamp, click on row 28 at the first empty cell east of the slab you just stamped, so the slab runs on over H5 to the east wall at x 624.
6. Click Save at the top of the Tilemap panel.

Pick

The tilemap painter’s Pick, I: a click reads one painted cell into the brush; a drag lifts every cell in its rectangle, on the chosen layer, as a block. It changes no cell.

Stamp

The painter’s Stamp, S: puts the lifted block down, its top left corner at the cell clicked, as often as you click. Merge, as it comes, leaves a cell alone where the block has none; Overwrite clears it.

The vent and its updraft

1. Select upper_hall, click + Add node and choose Sprite. Rename it vent and set its Position to 56, 672: on the floor, under H6. Drag art/vent.png onto Texture, and set Size to 64, 10, Anchor to 0.5, 0 and Sort Layer to 1. In the Draw mode fold, set Draw Mode to Tiled and Tile Size to 32, 10: the grating twice, hung from its top edge into the floor’s moss caps.
2. Select upper_hall, click + Add node and choose Effector. Rename it updraft and set its Position to 56, 672, the vent’s middle, on the floor.
3. In its Area, open Shape and set Size to 64, 320 and Offset to 0, -160. Click the button beside Mask, untick World, and tick Knight and Crate. Leave the Area’s Layer as it comes.
4. In its Effector, leave Kind at Directional. Set Acceleration to 0, -3200 and Max Speed to 400. Leave Priority at 0, and untick Enabled.
5. Click Add component and choose SpriteComponent. Drag art/draft.png onto Texture, set Size to 64, 320, Anchor to 0.5, 1 and Sort Layer to 1, and in Draw mode choose Tiled with a Tile Size of 16, 32: the draft’s streaks, up the column.
6. Click its Color. If the button at the top left of the picker reads U8, press it so it reads F. Leave red, green and blue at 1 and set alpha to 0: the streaks hidden, as the vent is shut.
7. In the Gizmos menu, Forces and Triggers are ticked, as chapter 9 left them: Forces draws each effector’s arrow, Triggers each Area’s outline. With updraft selected, move the pointer over the Viewport and press F to frame it.

The Effector’s Kind

The Effector’s Kind: which push it gives. Directional, as it comes, is one push, the same everywhere in its Area, along its Acceleration: a wind. Chapter 11’s belts are Surface and its magnets Point, chapter 12’s water Buoyancy. Each kind reads its own rows, and the others dim.

The Effector’s Acceleration

The Effector’s Acceleration, for a Directional wind: how hard it pushes and which way, across and down, in world units a second squared, added to every body in its Area each step. Down counts as positive, as a Gravity does, so up is negative. The updraft’s 0, -3200 is up, stronger than his Gravity of 2000 and a crate’s 1800, so it lifts both; it takes him up 20 faster each step, its 3200 less his 2000 at sixty steps a second. A new Effector’s is 0, -600.

The Effector’s Max Speed

The Effector’s Max Speed, for a Directional wind: the fastest it blows a body along its Acceleration, in world units a second. It adds only what brings a body’s motion that way up to the limit, and nothing to one already that fast; it never slows one. 0, as it comes, is no limit. The updraft’s is 400, the crosswind’s 200. The limit is on the body’s whole motion that way, its Velocity and its Drift together, not on what the wind gave: walking against a wind in the air, his walk is part of the sum the limit is measured on, and against the wind it leaves more room, so the wind banks him more Drift, and let go of the keys, that Drift carries him on the wind’s way faster than the limit for a while.

The Effector’s Priority

The Effector’s Priority: which wind blows where two overlap. Of every effector a body is in, only those at the highest Priority push it; those that tie add. A whole number, 0 as it comes. The updraft keeps 0; the crosswind, next, has 1.

The Effector’s Enabled

The Effector’s Enabled: whether it pushes right now. It comes ticked. The updraft is saved unticked, the vent shut, and vent.rgs ticks it when the lever says on and unticks it on off. The crosswind keeps it ticked.

The Area’s Shape › Size and Offset, on an effector

Where an Effector pushes: only inside the Area on its own node. The Area’s Size is the box’s width and height in world units and its Offset where the box’s middle sits from the node, as on the plate in chapter 4. The updraft’s 64 by 320, 160 up, is the shaft from the vent to over the loft. An Effector with no Area beside it pushes nothing, and the Problems tab says so.

The Area’s Mask, on an effector

Whom an Effector pushes: every body whose Character Body’s Layer the Area’s Mask ticks. The Area’s own Layer is not read for it, nor anyone’s Area. Every effector in the tower ticks Knight and Crate, chapter 5’s layers for his body and the crates’, so it pushes him and the crates. A new Area’s Mask ticks World.

The Sprite’s Color

The Sprite’s Color: a tint over the picture, red, green, blue and alpha, each 0 to 1 in the picker’s F mode. White, 1, 1, 1, alpha 1, as it comes, draws the picture as it is. The streaks’ alpha 0 draws them fully see-through: hidden, though the sprite is there, until vent.rgs sets alpha 1.

The crosswind

1. Select upper_hall, click + Add node and choose Effector. Rename it crosswind and set its Position to 96, 352.
2. In its Area, open Shape and set Size to 160, 64; leave Offset at 0, 0. Set Mask to Knight and Crate, as the updraft’s.
3. In its Effector, leave Kind at Directional, set Acceleration to 2400, 0, Max Speed to 200 and Priority to 1. Leave Enabled ticked.
4. Select crosswind, click + Add node and choose Sprite. Rename it crosswind_streaks and set its Rotation to 90. Drag art/draft.png onto Texture, set Size to 64, 160 and Sort Layer to 1, and choose Tiled with a Tile Size of 16, 32. Its Anchor stays 0.5, 0.5.

The lever and two scripts

1. Select upper_hall, click + Add node and choose Sprite. Rename it lever and set its Position to 112, 672: on the floor, east of the vent. Drag art/lever.png onto Texture, and set Size to 20, 24, Anchor to 0.5, 1 and Sort Layer to 1. Its handle leans west.
2. Click Add component and choose AreaComponent. Open its Shape and set Size to 108, 320 and Offset to -42, -160. Set its Mask to Knight alone. Its Layer stays World.
3. In Assets, click Create, choose New script, type vent_lever and press Enter. In the Code tab, replace everything in vent_lever.rgs with the first script below, and press Ctrl+S. Make vent.rgs the same way, with the second.
4. Select lever, click Add component and choose VentLever. Select updraft, click Add component and choose Vent.
5. Select lever, click Add component and choose SignalComponent. Click the + beside Connections twice. Open [0]: type on into Signal, and pick updraft for its To. Open [1]: Signal off, To updraft. Press Ctrl+S.

/// The vent's lever. Its Area reaches the lever and the shaft over the vent,
/// so the knight can throw it standing by it, on the vent, or riding the
/// draft. The `action` key (E) throws it over: it turns its handle and says
/// `on` or `off` to whoever its Signal wires them to.
component VentLever : Area {
    /// How many things its Area notices: one while the knight is in its
    /// reach, none while he is not.
    #[readonly]
    near: i32 = 0,
    /// Whether it is thrown on.
    #[readonly]
    on: bool = false,

    fn on_enter() {
        near += 1;
    }

    fn on_exit() {
        near -= 1;
    }

    fn loop() {
        if near > 0 && pressed("action") {
            on = !on;
            set_flag("SpriteComponent", "flip.x", on);
            if on {
                emit("on");
            } else {
                emit("off");
            }
        }
    }
}

/// The vent. The Effector on this node blows up the shaft while it is
/// switched on. The lever's `on` switches it on and shows the draft's
/// streaks; its `off` switches it off and hides them. A step that hears
/// both ends shut.
component Vent {
    fn on_signal() {
        if heard("on") {
            set_flag("EffectorComponent", "enabled", true);
            set_colour("SpriteComponent", "color", vec4(1.0, 1.0, 1.0, 1.0));
        }
        if heard("off") {
            set_flag("EffectorComponent", "enabled", false);
            set_colour("SpriteComponent", "color", vec4(1.0, 1.0, 1.0, 0.0));
        }
    }
}

component VentLever : Area

A script with an Area base, like chapter 8’s ring pull: it goes on a node with an Area and hears what comes into its reach and leaves it. Near counts the Areas in its reach, his; On says whether it is thrown on. Both are #[readonly]: the script sets them, and you never type them.

loop and pressed

loop runs every step. pressed("action") is true on the one step E or Enter goes down, the project’s action, so one press throws the lever once, however long it is held.

set_flag

Writes true or false onto another component on this node. In the lever, "flip.x" is the Sprite’s Flip › X, which draws the handle mirrored, leaning east while it is on. In the vent, "enabled" is the Effector’s Enabled.

emit

Says on or off to whoever the lever’s Signal wires them to, updraft, which hears it on the next step.

component Vent

A script with no base, like chapter 4’s door: it hears signals. on_signal runs on a step a signal reaches the node, and heard says which: on switches the Effector on and shows the streaks, off the reverse. A step that hears both ends shut, as the second if runs last.

set_colour and vec4

set_colour writes a colour onto another component on this node, and vec4(1.0, 1.0, 1.0, 1.0) makes one: red, green, blue, alpha. On the Sprite’s Color, alpha 1 shows the streaks and 0 hides them.

A crate in the way

1. In the Hierarchy, right-click crate_1 and choose Duplicate. Drag the copy onto upper_hall, rename it crate_7 and set its Position to 200, 672: on the floor between the lever and where he comes up. Press Ctrl+S.

Up the shaft

1. In the Gizmos menu, keep Collision, Bodies, Forces and Triggers ticked, as chapter 9 left them, for this chapter and the next. As on chapters 8 and 9’s pages, the pictures here leave Collision off: the Colliders’ green outlines are on your screen and not in them.
2. Select knight and set his Position to 489, 672. Then select updraft, so its arrow is drawn at full strength, as in the pictures, and press F5.
3. Hold A: he walks west. As he nears the crate, press Space and hold it until he lands beyond it. Keep A held until he stands on the vent, and let go. Nothing lifts him: the vent is shut.
4. Press E. The handle swings east, the streaks show up the shaft, and the draft lifts him. Hold nothing: it takes him up through H6, and at the top the crosswind blows him east onto the loft, where he slides to a stop.
5. Press F5 to stop, and set his Position back to 48, 1792.

Drift, read live

1. Select knight before you play, so the Inspector shows his Character Body while the game runs. Set his Position to 489, 672.
2. Press F5, ride up as before, and watch his Drift, under his Velocity. To catch each step of it, press Pause or F6 as he reaches the top of the shaft, then Step or F7, with the Play bar’s step counter.
3. Press F5 to stop, and set his Position back to 48, 1792.

The Character Body’s Drift

The Character Body’s Drift: what the world adds to the body’s own Velocity, in world units a second: a wind, a magnet, a belt, water, a shove, a swing. The body moves by the two together. For a body whose Motion Mode is Grounded, as his is, it is sideways only: a push along gravity, as the updraft’s, goes into his Velocity, as gravity does. It is read only, so its row is dim: nothing types it, the world writes it. The keys set Velocity every step and never overwrite Drift, so letting go of a key does not stop a wind’s push, and a wind’s push does not stop his walk; on chapter 13’s rope, the one place the keys reach his Drift, they push it. In the air it lasts; on the ground it fades by the floor’s grip. Here the crosswind grows it 40 a step, its 2400 at sixty steps a second, up to its Max Speed, 200.

1. Select crosswind and set its Effector’s Priority to 0, the updraft’s.
2. Set the knight’s Position to 489, 672, press F5 and ride up as before. Where the two boxes overlap, both winds now blow: the updraft keeps him rising at its limit into the crosswind’s box, so he goes higher before the crosswind has him, and lands further east.
3. Press F5 to stop. Set Priority back to 1 and the knight’s Position back to 48, 1792.

Shut it on the way up

1. Set the knight’s Position to 489, 672, then select updraft, as for the ride, and press F5. Walk onto the vent and press E.
2. Half-way up the shaft, press E again: the handle swings back, the streaks hide, and nothing holds him up. He rises a little further as his Gravity slows him, falls, and lands on the vent.
3. Press E from the vent: it opens, and up he goes again. Press F5 to stop, and set his Position back to 48, 1792.

A crate rides it too

1. Set the knight’s Position to 489, 672, then select updraft and press F5. The game camera follows him, and the crate will go far above him: press F over the Viewport, so the whole shaft is in view, as in the ride’s pictures.
2. Hold A: he walks to the crate and shoves it west onto the shut vent. Let go as it reaches the vent’s middle.
3. Hold D for a moment to step him back east, just past the vent’s east end and short of the lever: out of the draft’s column, still in the lever’s reach.
4. Press E. The crate goes up the shaft alone, and at the top the crosswind blows it east onto the loft. Press F5 to stop, and set his Position back to 48, 1792.

The way up

1. Set the knight’s Position to 489, 672 and press F5.
2. Hold A, jump the crate with Space held, and walk on onto the vent. Let go.
3. Press E. The draft takes him up through H6, and the crosswind sets him down on the loft. No key is needed at the top: his Drift lasts in the air.
4. Press F5 to stop, and set his Position back to 48, 1792.

The upper hall

Check it works