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SPROGS Paper No 40: SPROGS Version 2 - Extra Facilities

R E Thomas

December 3 1973

INTRODUCTION

Following discussion on Paper 39, it was decided that the following items should be included in Version 2, and that a 'glossy' manual should be produced. 

 (1)   Dotted (simple form)   
 (2)   THICK   
 (3)   Circle/ellipse scissoring   
 (4)   Colour   
 (5)   STCHSZ, GVCHSZ   
 (6)   IFS   
 (7)   STSQLS   
 (8)   SPSQLS modification   
 (9)   User display routines   
(10)  File deletion

In addition, some experiments will be conducted to see if COMPRESS INTEGER can be used, and facilities for owned tapes (with the removal of RETAIN) will be provided. If time permits, 'Advance Repeat' may be attempted.

USE OF SPECIAL DEVICE HARDWARE

The problem of making use of any particular hardware features was raised, initially in connection with using axes on the SD4020. Users who provide shading usually use axes to avoid breaks in intensity due to vector splitting (eg Colin Emmett). However, provision of this facility will lead to another test for all lines at the SD4020 device routine level, with subsequent slowing in line drawing. An intermediate possible solution to this would be the provision of two device routines: one as now and one with the option, which would be selected as in TOTAPE etc.

However, it raises other problems with devices such as the PDP15, which has 4 different vector types which may be selected, and for future devices which may have hardware facilities for intensity, thickness, dotted lines, etc, all of which are currently implemented in software terms. It may well be preferable to consider some general format which can make use of hardware. For example, a display routine VECTYP could give a bit setting which would indicate on the SD4020 and PDP15 the type of vectors required, and maybe another bit setting routine could supress software implementation of thick, dotted, etc, leaving it to the device selected (but could cause problems if more than one device required, only one of which has the requisite hardware). This will need to be discussed further.

BYPASSING REGIONS

Some potential users of SPROGS do not want to use any clipping or conversion. It is possible to have a short path through the regions by selecting the base region for the device and setting visibility to (1.0,1.0). However, it would be possible to bypass even this much, calling the selected devices directly, by selecting REGION (-1.0), say. Again, further discussion is required.

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