-- card: 6102 from stack: in
-- bmap block id: 0
-- flags: 0000
-- background id: 2619
-- name: HyperDA's Inner Workings


-- part contents for background part 3
----- text -----

HyperDA’s Inner Workings

-- part contents for background part 2
----- text -----

HyperDA will open any HyperCard stack.  When it does open a stack or when the browser switches cards, HyperDA builds a bit map of the complete image of the appropriate card in a memory location that is not in the normal video display memory region.  Technically, this is referred to as an off-screen bit map.  Once it has built this bit map, then HyperDA copies the entire image to the area of memory where the screen display is stored.  Because of this approach, the user never sees a HyperCard card being assembled.  It simply goes from being off-screen to being on-screen instantaneously.

What HyperDA displays at any given moment is a static bit image of the card itself; none of the dynamic components, including buttons, is included in the display.  (In fact, this is also how HyperCard itself works; its buttons are not part of the “normal” Macintosh Control Manager routines.  Rather, they are created and managed entirely by HyperCard.)  When the user clicks on an area of the card (e.g., a scrollable field or a button), HyperDA superimposes the appropriate dynamic element on the static image at the right location.