Tutorials · Particle Effects · Chapter 6

Flipbooks and spin

Flames from a sheet

1. Select forge_fire. Set Texture to flame-sheet.png.
2. In the same Sprite group, tick Texture Sheet. A new sheet is a strip of 4 by 1, so set Rows to 2 and Last to 7. Columns stays 4, First stays 0 and Driver stays Lifetime.
3. Press Ctrl+S, then F5 to see the flames, and F5 again to stop.

Texture Sheet

Switches on a sheet: the Texture is read as a grid of pictures, and each particle draws one of them at a time, not the whole image. The row is cut short in the Inspector as Texture …. Off, every particle draws the whole texture.

Columns, Rows

How many pictures lie across the sheet and down it, each at least 1. flame-sheet.png is 4 across and 2 down, so each flame is a quarter of its width and half its height. Count them from the picture and type them in: a wrong count draws a slice of two pictures at once.

First, Last

The pictures a particle plays, counted from 0 along the top row from the left, and then along the next row. Last is included. Here 0 to 7, all eight. A sheet of several animations is cut by these two: 0 to 3 plays the first row alone.

Driver

What picks the picture a particle draws. Lifetime walks from First to Last once, from birth to death, so every flame flickers through all eight pictures as it burns. Speed picks the picture by how fast the particle is going: the first when it is slow, the last from its Max up, as the next section’s sparks do. There is no clock that runs the frames by itself.

Sparks that point where they fly

1. Select forge_sparks. Set Texture to spark-sheet.png.
2. Tick Texture Sheet. The new sheet is already 4 by 1, from 0 to 3, which is what this one needs. Set Driver to Speed, and Max to 160.
3. Open the Rotation group and tick Align To Velocity.
4. Press Ctrl+S.

Max

With Driver on Speed, the speed, in world units a second, from which a particle draws the last picture. The speeds from 0 up to Max are cut into equal slices, one for each picture, and a particle draws the picture for the slice it is in. Here 160, the top of the sparks’ Speed Range, so four slices of 40: below 40 the dot, then two streaks, and from 120 up the longest. A spark leaving at 110 draws the third picture and rounds off to a dot as it slows. Zero pins every particle to the first picture.

Align To Velocity

Turns each particle to point along its own flight, so a streak lies the way the spark is going. It takes the place of any spin: Start Rotation, Rotation Spread and the spin below are ignored while it is ticked.

Smoke that turns

1. Select Town, press + Add node and choose Particles. Rename it forge_smoke, and set its Position to 114 and 246, above the forge’s stone.
2. Set Rate to 8, Lifetime to 3, Speed to 16, Direction to 0.1 and -1, Spread to 0.3 and Gravity to -5.
3. Set Start Color to 0.42, 0.42, 0.45, alpha 0.65, and End Color to 0.35, 0.35, 0.38, alpha 0.
4. Set Start Size to 10, End Size to 30, Capacity to 32 and Sort Layer to 1, behind the forge’s stone, which is on 2, so the smoke shows above it.
5. Set Texture to smoke-sheet.png, and tick Texture Sheet: Rows 2 and Last 7, as for the fire. The smoke’s eight pictures are puffs, and Lifetime walks them as it thins.
6. Open Rotation. Set Start Rotation to 0, Rotation Spread to 6.3, Angular Velocity to 0.6 and Angular Velocity Spread to 1.6.
7. Above, in Over Lifetime, tick Rotation Over Life and open it. Click the right point and set its y to 0.2, as in chapter 5; the left point stays at 1.
8. Press Ctrl+S.

Start Rotation

The angle each particle is born at. In the scene file it is in radians, and the Inspector shows it in degrees, as 0°. At 0° a picture is drawn as it is on the sheet, upright. Here 0°, with a spread round it.

Rotation Spread

A random width round Start Rotation, in radians: each particle is born within half of it either side. 0 gives every particle the same angle; a whole turn is 6.28. Here 6.3, a little more than a whole turn, so each puff starts at any angle. 0 to 7 is its range.

Angular Velocity

How fast each particle spins, in radians a second; a negative number turns it the other way. 0.6 is a slow turn, a little under a tenth of a revolution a second. 0 to 1 suits smoke, and a leaf or a chip of debris wants 2 or 3.

Angular Velocity Spread

A random width round Angular Velocity, in radians a second, as Rotation Spread is round the angle. Here 1.6, wider than twice 0.6, so some puffs spin the other way. 0 gives every particle the same spin.

Rotation Over Life

A curve that multiplies the spin, not the angle, across a particle’s life: 1 leaves it, 0 stops the turn. Here 1 at birth and 0.2 at death, so a puff turns briskly as it leaves the forge and almost stops as it thins out. The curve is drawn as the other over-life curves are, in chapter 5.

What a sheet costs

The forge fire, the forge sparks and the forge smoke

Check it works