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Author: Dan Ludwig | Website:

Without the "if" statement, scroll_shape would keep traveling above the uppermost constraint we have set for it (the top variable). By setting a condition for the "setProperty" action to take place, we can ensure that this loop will never execute an infinite number of consecutive cycles (whoa). What I mean is that the user can hold down a scroll button, but as soon as the parameters in the "if" statement return a false value, the "setProperty" action will cease being executed. So, in order to make the "if" condition return a false value when the uppermost (top) limit is reached, we insert an inequality expression as the"if" argument. As long as scroll_shape's _y value is greater than or equal to (in other words, visually below) the uppermost constraint defined as top, the "setProperty" action will be executed. As soon as scroll_shape's _y value becomes less than top though, the "setProperty" action is avoided by the script.

You might be wondering why that extra 0.1 was added to the right side of the inequality expression. Again, this was tacked on as a tweaking measure. There is a reason why I made each "setProperty" action move in increments of only one pixel; to maintain visual integrity when combining drag scrolling with button scrolling in Flash. A more well planned design would embed each scroll button into its own MC, then access their dimensions from the code to calculate the distance scroll_shape can travel. It is very likely, if you use "setProperty" to increment in amounts larger than 1 pixel at a time, that scroll_shape will end up colliding with/overlapping your button(s). This looks tacky, and it looks even worse when scroll_shape snaps back into place after clicking it. The 0.1 here, like the 0.8 in cfb_logic_down, compensates for changes that occur when combining drag scrolling with click scrolling in Flash.

The ActionScript for cfb_logic_down is constructed similarly to cfb_logic_up, although the arguments are different:

if (((getProperty(_root.scroll_shape, _y))<=(_root.scroll_shape.logic.bottom)-.8)) {
  setProperty ("_root.scroll_shape", _y, _root.scroll_shape._y+1); }

This time scroll_shape's _y value must be less than or equal to bottom in order for the "setProperty" action to be valid. Again the tweak value is 0.8, and scroll_shape's _y value gets 1 pixel added to it, thus moving scroll_shape down.

» Level Intermediate

Added: 2000-12-08
Rating: 8 Votes: 94
(10 being the highest)
» Author
Me Like Flash 5. Flash 4 good. Flash 5 better.
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