The SPROGS system manual has now been officially released, font numbers one and two being an integral part of that system. The purpose of this paper is to provide the user with a glimpse of their history.
After initial discussions it was decided that there would be two basic fonts, each being sixty-four characters in length: the one essential difference being the upper and lower case alphabets. Before work began, references were made to a number of existing fonts in graphical manuals to provide a guideline for the design.
The work on the individual characters of each font was done using a font generation program available on the PDP15 computer with a VTO4 refreshed display.
The program consists of a number of overlays. The first enables the user to design the individual characters using the display screen and the light pen, the structure of the character being easily changeable. When a suitable design was found the character was then stored in a specific file on a DEC tape.
The second overlay allowed the user to pack up a set of characters onto disc to be used with later overlays.
A rough draft for the two fonts was completed and they were then checked in their true context (strings of text) using the next overlay of the program. Frames of characters were made up from the two fonts and were subsequently stored. The frames comprised strings of text of varying sizes interspersed liberally with punctuation.
Overlay number four output the frames to magnetic tape in a form suitable for the SD4020 microfilm recorder. A set of hardcopies was made and distributed to each member of the graphics section. As a result, comments and suggestions were put forward for improvements, which proved to be most informative with regard to techniques in character design. There follows a fairly detailed list of the suggestions which were put forward and the action which was taken:-
1. When the characters were small it as difficult to distinguish between the comma and the full-stop. Originally, the comma was designed to resemble an inverted triangle. This was changed so that now it appears as a full-stop with a tail. The same trouble arose with colons and semi-colons.
2. The lower-case characters o, a and c were difficult to tell apart. To correct this, the 'a' was given a more pronounced tail whilst the 'c' was given a completely flat bar at the top and bottom.
3. The dot at the base of the exclamation mark, which merely consisted of a vertical line one raster position in length, was not clearly defined. An inverted triangle replacing the line proved to be more successful.
4. The capital D resembled the capital O. A more pronounced curve in the D corrected this.
5. The lower case 's' and 'e' were completely indistinguishable when the size was small. To correct this a flat bar was given to the top and bottom of the 's' and to the bottom of the 'e'.
6. One aspect existed in the design of the characters which could not be corrected. This was due to an optical illusion. Characters having a base line, such as a B, C or D, appeared to lie lower on the line than letters with a tail such as P, R or T.
7. From recent observations there is one general point which has not yet been discussed. When designing characters on a 16 × 16 grid it is important to note that the individual lines which form the structure of the character should be at least two raster positions apart. If this general rule is not observed, that section of the character will appear as a dark area because the lines tend to merge together, particularly when the characters are small.
The fonts, having been improved considerably, were then ready to be placed into the SPROGS system.
Using overlay number six, paper tapes were generated, one for each font, which consisted of a series of calls to routines in SPROGS for picture file definition. These paper tapes were in 1906A code, and were read directly into the GEORGE file store. The routine calls always referred to both co-ordinates, which was unnecessary if one of them was zero and a subsequent edit was performed. To quote a specific example:-
CALL TODXY (-12.0, 0.0) can be written as
CALL TODX (-12.0)
Using basic editing instructions, the two paper tape files were considerably reduced in size.
However, before finally being placed in the system some test programs were run in order to check that the inclusion of the fonts gave a satisfactory performance.
Work on the fonts was finally completed with the production of a loose-leaf manual, which supplies information about each character for the benefit of users.