Containers, Grid Co-ordinates and Gadget Boxes

The Form and its Frame gadgets act as containers for holding gadgets. Typically gadgets are laid out in their containers from left to right and from top to bottom. Each container has a rectangular co-ordinate grid with origin (0, 0) at the top at the top left-hand corner.

Each gadget has an origin at its top left-hand corner and a width and height, which together define a notional gadget box, which contains the gadget including its tag-text if defined. Layout involves positioning each gadget, by its origin, at a specified position within the grid of its container and indicating its width and height.

• The grid horizontal pitch is the notional character width for the system font. Because this font is variably spaced, n horizontal grid units do not equate to n characters. Generally, it is more than n unless the string has a high proportion of wide characters for example, capitals, numerals, w's, m's It is important that you understand this concept when you specify gadget sizes.

• The grid vertical pitch is the line-height, which is the height of the tallest of the textual gadgets: TOGGLE, BUTTON, OPTION, TEXT or single-line PARAGRAPH.

Figure 17:1. Conceptual X and Y Coordinates

For the Form container its extremities are referred to as XMIN form, YMIN form, XMAX form and YMAX form.

The extremities of a gadget box are referred to as XMIN.gadget, YMIN.gadget, XMAX.gadget an YMAX.gadget.

Figure 17:2. Gadget Box Extremities

When new gadgets are added to a container, the XMAX and YMAX extremities grow to include the gadget boxes.