mathew@jane.jpl.nasa.gov (Mathew Yeates) (07/26/89)
I'm trying to download a character set to my vt240 and I'm supposed to use something called "sixel bit patterns". I've got a Graphon manual which uses the word "sixel" once and only once. The vt240 users guide says a bit more but not enough to be helpful. Specifically, in my escape sequence I'm supposed to enter something of the form S...S/..S for each character. Anybody know anything about this? -mathew mathew@jane.jpl.nasa.gov
leichter@CS.YALE.EDU (Jerry Leichter) (07/26/89)
In article <1989Jul26.075128.19329@elroy.jpl.nasa.gov>, mathew@jane.jpl.nasa.gov (Mathew Yeates) writes... >I'm trying to download a character set to my vt240 and I'm supposed >to use something called "sixel bit patterns". I've got a Graphon >manual which uses the word "sixel" once and only once. The vt240 >users guide says a bit more but not enough to be helpful. > >Specifically, in my escape sequence I'm supposed to enter something of >the form S...S/..S for each character. Anybody know anything about this? > > >-mathew >mathew@jane.jpl.nasa.gov This is all documented in the VT240 PROGRAMMER'S guide, which even gives a worked example. Basically, it's simple: The sixel protocol is a way of encoding bitmaps in "typeable" characters. A VT240 character cell is 10 bits high and either 6 (132-column) or 8 (80-column) bits wide. Write out your character as (say) a 8x10 array. Draw a line between the 6th and 7th rows. The 6 rows above are the upper columns; the 4 below are the lower. Proceed left to right, column by column, across the upper columns. For Take the 6 bits in a column and consider than as a binary number, with the least significant bit at the top. Evaluate that number and add 77 base 8 (i.e., 63). The result is the sixel encoding for those bits. Write out the encoding for all the columns from left to right, then add a "/". Now go back and do the lower columns. This time, consider them as 4-bit binary numbers; the top bit remains the most significant one. In case you are wondering where this bizarre encoding came from: It was originally designed for sending bitmaps to simple pin-head printers, which had 6 pins and had to move across the page from left to right, filling in 6 rows before they could go back and do the next 6. As often happens, the encoding lived on in very different environments.... -- Jerry