From: branimir.maksimovic@gmail.com   
      
   On 2021-07-14, James Harris  wrote:   
   > On 14/07/2021 14:56, James Harris wrote:   
   >   
   >> Is there already a good standard way to interface with a textual   
   >> display? What I'm looking for is a pre-defined set of calls which I can   
   >> just implement rather than having to design from scratch.   
   >   
   > As a sub topic, I gather there are standard ways to implement a   
   > 'terminal' which will work with both a VDU and a machine which prints   
   > characters on paper instead of a screen.   
   >   
   > For example, with paper a backspace cannot delete the previous character   
   > (unless it's a space) but there are other options. The terminal could:   
   >   
   > 1. print a certain character to indicate the backspace such as ~ in   
   >   
   >    prant~~~int   
   >   
   > (to form the word "print")   
   >   
   > 2. back up and overwrite any character which is no longer present in the   
   > buffer as with   
   >   
   >    pr@@@int   
   >   
   > where @ represents some form of overwritten characters.   
   >   
   > Similarly, on a VDU a backspace could, effectively, be written as   
   >   
   >    backspace, space, backspace   
   >   
   > but in any case the point is that there's a translation between what a   
   > program would work with (the backspace in this example) and how it gets   
   > rendered on the terminal.   
   >   
   > I don't anticipate really using a paper-feed teletype, and backspace is   
   > not the only issue but I would still like there to be a translation   
   > layer between a program and whatever is used as a text-display device.   
   >   
   > I know there are various standards for terminals but my experience of   
   > them has - literally for decades - shown that it's difficult if not   
   > impossible for a user to get both ends (OS and terminal) to work   
   > together consistently.   
   >   
   > On top of that I gather there are various standards for how terminal IO   
   > translations can be specified - such as what text to print in   
   > bold/bright, where a certain piece of text should appear, how to ask for   
   > a line to be reprinted, etc, but I know almost nothing about them.   
   >   
   > Hence the question: would you recommend any particular translation layer   
   > (between OS and the gamut of terminal devices) or would it be better,   
   > these days, to design one's own?   
      
   Terminal just sends escape characters to serial port. OS interprets those   
   based on termcap file.   
   Terminal also understands escape characters so that it can move cursor   
   around,\underline,   
   bold and such. Terminal doesn't connect directly to printer.   
   >   
   >   
      
      
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