Changing the environment of a job between pages
This page applies to Harlequin v13.1r0 and later; both Harlequin Core and Harlequin MultiRIP.
Sometimes it is necessary to change the environment (namely, whether or not you are doing imposition) between pages. Where the data affected is global, this is straightforward—it is just changed in BeginPage
or EndPage
as required. Global data includes system parameters.
However, when the data is subject to save
and restore
, or gsave
and grestore
, such as the graphics state or local VM, it is likely not to survive.
A good example of this is overriding the screen angles in a pre-separated job. Such jobs often go:
currentscreen exch pop angle
exch setscreen
near the beginning of each page. While the Harlequin RIP has system parameters which override the screen frequency and spot function, or the whole screen, in Version 3.2 there is no parameter for screen angle alone. However if, for example, the BeginPage
procedure calls sethalftone
with the Override
flag set to prevent the job from then changing screens, the new value is restored back to the previous screen immediately (probably the one set by the very first BeginPage
).
In this case, record the value required for the current page in global memory in BeginPage
and apply it every time the job tries to change things for itself, by redefining the operator. The redefinition could be done in userdict
, as the following example illustrates, but might be better done by shadowing the operator, details of which are given in Shadowop and operator redefinition.
userdict begin
currentglobal true setglobal
/ScreenDict 2 dict begin
/AnglesRequired [15 75 0 45] def
currentdict
end def
setglobal
/setscreen {
% must also redefine setcolorscreen and sethalftone!
//ScreenDict begin
exch pop AngleForThisPage exch setscreen
end
} bind def
<<
/BeginPage { % page count on stack
//ScreenDict begin
/AngleForThisPage AnglesRequired 3 -1 roll 4 mod get def
end
} bind
>> setpagedevice
currentdict /ScreenDict undef
end