 | | | smooth scrolling/subpixel tweening | smooth scrolling/subpixel tweening 2003-11-23 - By Robert Tweed
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A few pointers:
1 - Don't use updateStage, ever.
2 - Don't animate in repeat loops. Use frame events instead. Use enterFrame
or stepFrame to do the majority of your processing, as these events get the
biggest CPU timeslice.
3 - To animate in fractions of pixels, simply store the position in a
property, which can have fractional values. For example, use pLoc for the
loc, then at some point do pSprite.loc = pLoc. The sprite loc will be
converted to an integer value, but internally, you will still be working
with floating point.
Wherever possible, avoid complex formulae like this:
> pY = (-0.32 * power(abs(pX - 5), 2)) + pB
Try to stick to simple addition and subtraction as much as possible. To do a
jump, simply use values that represent force vectors. Here's an example of
some simple platformer code (needs some blanks filled in) - notice simple
the mathematical stuff is:
property pSprite, pLoc, pDir, pOnFloor
global gLeftKey, gRightKey, gJumpKey
global gGravity -- e.g., point( 0, 0.5 )
on beginSprite me
pSprite = sprite( me.spriteNum )
pLoc = pSprite.loc
pDir = point( 0, 0 )
pOnFloor = false
end
on prepareFrame me
h = 0
if( keyPressed( gRightKey ) ) then h = h + 4
if( keyPressed( gLeftKey ) ) then h = h - 4
pDir.locH = h
if( keyPressed( gJumpKey ) ) then me.jump()
end
on jump me
if( pOnFloor <> true ) then return
pDir.locV = -7
end
on enterFrame me
pOnFloor = false
pDir = pDir + gGravity
newLoc = pLoc + pDir
pLoc = me.checkCollisions( newLoc )
pSprite.loc = pLoc
end
on checkCollisions me, newLoc
if( me.hitFloor( pLoc, newLoc ) ) then
newLoc = me.intersectWithFloor( pLoc, newLoc )
pDir = point( 0,0 )
pOnFloor = true
end if
return newLoc
end
on hitFloor me, loc1, loc2
-- Check to see if hit the floor
end
on intersectWithFloor me, loc1, loc2
-- Return point where vector instersects floor
end
- Robert
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