(v13) HqnLayout color bar and control strip construction

This page applies to Harlequin v13.1r0 and later; both Harlequin Core and Harlequin MultiRIP.

Color strips and color bars are defined as a hierarchical structure to enable easy re-use of individual components. It would be possible to define an entire control strip in a single ControlBar object, but it is generally more useful to use indirect references by including the names of subsidiary objects rather than in-place definitions with arrays and dictionaries.

• A Patch is most commonly a single area of color, although more complex patches, such as the print feed icon or a “Harlequin at Heart” logo, may be defined as a single special patch. There is no specific object defining a single patch; rather they are defined by constructing a regular grid of patches in a Block.
• A BlockSet is a collection of Blocks that display much the same data, but they use different amounts of space. Thus, a BlockSet may contain step wedges for CMYK inks; one Block in the BlockSet may contain patches for 25, 50, 75, and 100 of each ink, while another might contain 10 steps at 10% increments. As the control strip is dynamically constructed to fill the space required, the software selects to show one of the Blocks from the BlockSet for best results.
• A BlockSequence object is a series of BlockSets; a Strip object is defined as a combination of a BlockSequence with additional metadata to set exact positioning, and so on. To build a color bar, the software first calculates the physical length of each Block in the Strip. It then works through all the BlockSets, selecting one Block from each to display. In most cases it  chooses the longest Block in each BlockSet, unless there is insufficient space available for all BlockSets to be represented in the output if that is done. Once all BlockSets are handled once, it cycles around through them again as many times as  required to fill the remaining space.
• A ControlBar object defines a whole color bar or control strip¹, and comprises some metadata plus a collection of Marks and a collection of Strips. In all cases, the component parts of a structure may be provided literally, or as a procedure that builds an equivalent structure; therefore a Block may be defined explicitly as (for example):

            /Prog3x1 <<
              /Colors [ [ { 1 1 0 0 }{ 0 1 1 0 }{ 1 0 1 0 } ] ]
              /Rows 1
              /Columns 3
              /ColorSpace/DeviceCMYK
              /TopLabel [ [ (CM) (MY) (CY) ] ]
              /TopLabelAlign /Center
              /TopLabelTransCharstrue
              /BottomLabel /None
            >>

Alternatively, it may be built using one of a set of support procedures, (for example):

/CMYKGrad { /Grad BuildCMYKWedge }

^1. The terminology used in the Harlequin RIP uses the phrases “color bar” and “control strip” for structures that vary only by whether one of the component marks is a text slug line. They do not differ in their fundamental construction.