I define a transformation frame relative to some rectangle. I'm basic
data structure used for graphics.
I represent two groups of distances:
- The fractional distance (between 0 and 1) to place the morph in its
owner's bounds
- Fixed pixel offset to apply after fractional positioning (e.g., "10
pixel right of the center of the owner")
!! API usage
It is important to understand that it is better to use the fine grained
API using elementary distances (bottomFraction:, bottomOffset:,
leftFraction: ....) than the ones (historical) using points and
rectangles (fractions:offsets:)
The reason is that the old API (fractions:offsets:) is only interesting
if you already have a rectangle and point at hand. If you need to create
new ones, then they are created for nothing because they will be
destructured to extract their information to be feed into the layoutFrame.
So please do not blindly copy and paste code!
Example:
Favor
(LayoutFrame identity
leftFraction: 0;
yourself);
(LayoutFrame identity
leftFraction: 0.5;
rightFraction: 0.95;
(LayoutFrame identity
topOffset: topHeight;
bottomFraction: 0;
bottomOffset: self buttonsBarHeight;
leftOffset: -1;
rightOffset: 1)
over
(LayoutFrame fractions: (0 @ 0 corner: 1 @ 1))
For this one in particular it is better to use
LayoutFrame identity
It is faster and more readable
because you are creating for nothing a new rectangle and some points.
!! Final point: Do not use Rectangles for specifying layoutFrames
If you happen to need to create a rectangle and use the
fractions:offsets: class methods, refrain from creating a rectangle.
The reason is that a rectangle is not 4 numbers, it represents a space
area and when you use a rectangle to represent random numbers you end up
creating rectangles with negative extents and this is not good.
In this case use Margin, Margin is a nice class holding either one
number (the same "margin" on the four sides of a rectangle), or two
number (top/bottom, left/right margins) or 4 numbers.
!! Implementation
Instance variables:
The fractional distance (between 0 and 1) to place the morph in its
owner's bounds is represented by the following instance variables:
leftFraction
topFraction
rightFraction
bottomFraction <Float>
Fixed pixel offset to apply after fractional positioning (e.g., "10
pixel right of the center of the owner") is represented by the
following instance variables:
leftOffset
topOffset
rightOffset
bottomOffset <Integer>
