About Hidden Objects

Ordinarily, the drawing process (more of a plotting process) is cumulative. Each time a window is redrawn, all objects that have been drawn since the last 'CLEAR' mnemonic are drawn again.

Where items plainly obscure or cancel each other, Visual PRO/5 will remove the hidden object from the draw list, thus optimizing the drawing process. You can help with this by using the 'PUSH' and 'POP' mnemonics to remove transitory drawn items.

Only two situations can be reliably and automatically optimized. They are as follows:

• The draw mode is either "copy" or "not copy". If a filled, non-rounded 'RECT', opaque 'PLOTTEXT', or 'IMAGE' completely covers any 'ARC', 'ELLIPSE', 'IMAGE', 'LINE', 'PLOTTEXT', 'POLYGON', 'POLYLINE', or 'RECT' then the covered item is removed. This only happens if no tool changes or 'PUSH' markers exist between the covered item and the new, covering item.

• All of the following conditions exist:

• • An arc, ellipse, line, polygon, polyline, or rectangle covers an exactly identical drawn object.

  • Draw Mode is set to XOR.

  • There are no tool changes or 'PUSH' markers between the old object and the new object.

  • The old object is removed from the draw list and the new object is not added. The new object is still drawn to effect the XOR.