Unexpected behaviour with sprite user vars

pobtastic

Run it first with the lines commented, you see what you'd expect "0.000000" x 2.

spr = createSprite()
spr.pos = {}

loop
  clear()

  printAt( 0, 0, spr.pos.x )
  printAt( 0, 1, spr.pos[0] )

// This line causes an "Invalid variable access".
//  spr.pos.x += 1

// This line causes a hard crash!
//  spr.pos[0] += 1

  update()
repeat

If we change the initialisation to;

spr = [
  .pos = {}
]

...then it works just fine as expected!

vinicity

I didn’t know you could assign an empty vector?

Does it work if you do spr.pos = {0, 0, 0} instead?

PB____

I think all trailing zero's can be skipped (so not just the fourth one :) ). I've used {} several times and haven't had issues with it (other than that opacity defaults to 0).

To me this seems like a bug, but I could work around it in the following way:

spr = createSprite()
spr.pos = {}

loop
  clear()
  var pos = spr.pos
  printAt( 0, 0, pos.x )
  printAt( 0, 1, pos[0] )
  pos.x += 1
  pos[0] += 1
  spr.pos = pos
  update()
repeat

It's not ideal, but I hope it helps :)

pobtastic

Oh yeah, I'd already worked around it - it was just a bit of a surprise to see the hard crash! :)

Willpowered

@pobtastic Thanks for the report. I can confirm that in the next patch the hard crash is fixed but also that for the time being spr.pos still cannot be manipulated in either of these ways (It's on our to-do list). PB's workaround is the intended way to do this currently- Pull out the variable from the sprite, manipulate it, and then put it back in the sprite.

Martin

Use spr.x and spr.y maybe ? Or setSpriteLocation(spr, x, y)

Or am I taking the example a bit too literally? :P

pobtastic

Oh yeah, the point is to be able to manipulate a vector other than the sprites own properties. I actually found this ages ago, I just randomly fired up a version of Jet Set Willy I have and found it again. The issue there being that, the characters "walk across the frame" and you only change sprite x once the tracking x reaches % 8 == 0.

Something like this;

// Work out the current frame based on the tracking "x".
game.guardians[id].frame = ( int( game.guardians[id].pos.x ) >> 1 ) & 3

// Only update the sprite "x" on a byte boundary.
if game.guardians[id].pos.x % 8 == 0 then
  game.guardians[id].x = game.guardians[id].pos.x
endIf

// Change frames based on movement, and not time.
setSpriteAnimFrame( game.guardians[id], game.guardians[id].frame )