Implementing and testing the overtyping behavior in the 1052 Emulator - part 2

TEST WITH MODIFIED FONT AND STARTUP STRING

I reloaded the font with the Putty configuration to be certain it is using the modified version I created with FontForge. The 1053 Emulator started up and wrote out a sequence of a quad, a Zero Width Joiner (ZWJ) and a quote character. This should cause Putty to render this as a composite quad-quote character instead. 

It did not. Frankly I am losing faith in the ability of Putty to create composite characters with the APL font. Many online searches claim that it works fine, allowing you to combine emojis and do other composite work, but the actual Putty document is silent on the issue. I suspect that the quality of online searches is the problem here.

ALTERNATIVE TO SUPPORT APL AFTER FAILURE TO SHOW COMPOSITES

The strategy now is to change the selection code to a special one that displays the actual composite character which exists as a single character in the APL385 font. When we are adding a selection code to a column where there was a previous entry, we look for the special cases that exist with APL for the 1130. We insert the special select code in the line buffer and remove the two separate characters that requested it. 

The routine to convert a selection code to a character from our typeball Unicode strings will have to recognize the special code and insert the proper glyph for printing. A means of doing this has to be devised. We also need to efficiently do the check for dual characters and replacement operation from the paragraph above. 

I have the source code of APL for the 1130 which allows me to grab all the possible overtyped characters it produces. Once I correlate these to the printed composite that would appear on the 1053, I can look up the glyph in the APL385 font and record that Unicode value. I found eighteen such combinations.

For example, the exclamation glyph (!) does not exist on the APL type element, so it is formed by a quote, backspace and period. The character for logarithm is formed with a circle, backspace and star. 

I experimented and was able to find the correct glyph to display for all 18 of the combinations issued by 1130 APL. I tried these characters on the 1053 Emulator and they displayed perfectly. 

DEBUGGING THE MODIFIED CODE

I have been debugging the code on Wokwi.com and it is working fairly well. I still need to test some edge cases to be certain it works okay, but it has been displaying the composite character when I type one part, backspace, and then type the other character from the APL typeball.