[Contents] [Index] [Help] [Retrace] [Browse <] [Browse >]

Intuition draws lines between points that are specified as sets of X, Y
coordinates.  Border data does not have to be in Chip memory.

The XY field contains a pointer to an array of coordinate pairs.  All of
these coordinates are offsets relative to the Border position, which is
determined by the sum of the external and internal position components as
described above.  The coordinate pairs are ordered sequentially.  The
first two numbers make up the first coordinate pair, the next two numbers
make up the second pair, and so on.  Within a coordinate pair, the first
number is the X offset and the second number is the Y offset.

The first coordinate pair describes the starting point of the first line.
When the Border is rendered, a line is drawn between each pair of points.
The first line is drawn from point one to point two, the second line is
drawn from point two to point three, and so on, until the final point is

The numbers specified in the XY array may be positive or negative.
Negative values move up and to the left relative to the Border position,
positive values move down and to the right. Again, the Border position is
determined by adding the external position component and the internal
position component.  For example, a Border attached to a Gadget has an
external component equal to the upper left corner of the gadget's select
box.  The internal component is set within the Border structure itself.
These two components are added together and offsets from the resulting
position, specified within the XY array, determine where the lines of the
Border will appear.

Suppose the top left corner of the select box of the gadget is at window
position (10,5).  If the Border has LeftEdge set to 10 and TopEdge set to
10, then the Border is positioned at (10+10,5+10), that is (20,15).  All
XY coordinates will be relative to this Border position.  If the XY array
contains `0,5, 15,5, 15,0', then the relative coordinates will be (0,5),
(15,5) and (15,0).  Adding each coordinate to the Border position gives
the absolute position of the lines within the window.  This Border will
draw two lines in the window, one from (20,20) to (35,20) and the second
from (35,20) to (35,15).

          0    5   10   15   20   25   30   35   40   45   50
          |         |         |         |         |         |
          |   Top left corner of the
          | gadget's select box (10,5)
       5 _|         * _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
          |         |
      10__|                Border          Third
          |         |     Position       Coordinate
          |                (20,15)      (20+15,15+0)
      15 _|         |         *              *
          |                                  |
          |         |                        |
      20__|                   *______________*
          |         |       First          Second
          |              Coordinate      Coordinate
      25 _|         |    (20+0,15+5)    (20+15,15+5)
          |         |

             Figure 8-3: Example of Border Relative Position

To create a border that is outside the select box of a gadget, specify
negative values in the internal component or use negative values for the
initial XY values.  For example, setting LeftEdge to -1 and TopEdge to -1
moves the position of the Border one pixel above and one pixel to the left
of the gadget's select box.

[Back to Amiga Developer Docs]