8-particle-galore.md

8. Particles Galore

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Lets add some confetti!

There is no particle system in PICO-8. However you can easily code one yourself. One simple system is to just draw a bunch of circles going in some direction. To keep track of all particles to draw we can initiate the program with a PARTICLES table in _INIT.

FUNCTION _INIT()
 PARTICLES={}
 -- SNIP-SNIP
END

Lets assume particles have a draw and an update function. We can go over the array and call them in the _DRAW and _UPDATE functions. To make sure we draw the particles under everything, so they don't obscure anything else, we draw them first after the CLS call.

FUNCTION _DRAW()
 CLS()
 FOR P IN ALL(PARTICLES) DO
  P:DRAW()
 END
 -- EVERYTHING ELSE
END

FUNCTION _UPDATE()
 -- DOESN'T MATTER WHERE YOU PUT THIS REALLY
 FOR P IN ALL(PARTICLES) DO
  P:UPDATE()
 END
END

Lets also assume that we create an ADD_PARTICLES function that will add particles with the given position and color. Lets use that whenever a cherry has been picked up!

-- IF YOU RECALL THE IF STATEMENT IN _UPDATE()
IF DIST(PLAYER, CHERRY)<4 THEN
 DEL(CHERRIES, CHERRY)
 SCORE+=1
 ADD_PARTICLES(
  10, -- AMOUNT OF PARTICLES TO ADD
  CHERRY.X, -- X
  CHERRY.Y, -- Y
  8 -- COLOR RED
 )
END

Drawing a particles should be simple, drawing a circle can be done with CIRCFILL. The only thing we need is the position, radius size and color which we can assume is in the particle data:

FUNCTION DRAW_PARTICLE(P)
 CIRCFILL(P.X,P.Y,P.SIZE,P.COL)
END

The function for updating a particle is a bit more involved. It should update the position and the time it needs to be alive. Assume we have a time parameter that we increase each frame T and the time it may be alive TO and remove the particle from PARTICLES once the time has passed. Assume we also have difference in x and y (a velocity) to update the position with.

FUNCTION UPDATE_PARTICLE(P)
 P.T+=1
 P.X+=P.DX
 P.Y+=P.DY
 IF P.T > P.TO THEN
  DEL(PARTICLES, P)
 END
END

With all the planning above, adding particles should be creating tables for each particle that can be drawn and updated. For the velocity, we can randomize an angle (in PICO-8 the angles are given in TAU rather than Degrees or Radians. Keep in mind that one rotation is between 0 (0 degrees) and 1 (360 degrees)). The dx and dy can be given with the trigonometry functions SIN and COS.

The function for adding particles may be written like this:

FUNCTION ADD_PARTICLES(N,X,Y,COL)
 FOR I=1,N DO
  LOCAL A=RND(1) -- randomize an angle
  ADD(PARTICLES, {
   X=X,
   Y=Y,
   COL=COL,
   DX=SIN(A)*(1+RND(5)), -- between -5 and 5
   DY=COS(A)*(1+RND(5)), -- between -5 and 5
   T=0, -- initiate timer
   TO=RND(5)+5, -- time out, remove after 5-10 seconds
   SIZE=1+RND(2), -- random radius between 1-3 pixels
   DRAW=DRAW_PARTICLE,
   UPDATE=UPDATE_PARTICLE
  })
 END
END

The game should look sort of like this:

Points to review

• Draw filled circles with CIRCFILL.
• Trigonometry functions exist in the PICO-8 API such as SIN, COS.

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