GOOD COMPUTER: LCD graphics

2020-07-06 19:44

I had an idea

2020-07-06 23:31

not a real clock, just text layout tests

I have several ideas

2020-07-07 19:24

dropped in this 5x8 font to get 25 chars per line. I love my C64 but really I’ve got limited space and this is quite readable

(this is the very pleasant “klostro” font by Anton Lazarev https://gitlab.com/antonok/klostro)

2020-07-08 19:28

building up 2D primitives. here’s line drawing

2020-07-08 20:34

PSA

2020-07-09 11:45

the big glitch there is a actually the CPU resetting in the middle of the data stream, which confuses the display. the bigger question is how is that even possible? has to be a power issue, which means I have to start thinking analog again, not my strong suit

2020-07-09 21:23

turns out AVRs can tell you why they reset, and it turned out to be the watchdog reset! since I’m not using, something enabled it. which means something randomly wrote to its control register. and since the only thing I’m writing to is the bitmap buffer, my math must be at fault

2020-07-09 21:26

so I dumped the x&y and memory targets for every plot, and tracked it to this line, then ran through the math by hand. on left, normal human math. on right, 8-bit signed math with overflows. of course, -196 is not expressible in 8-bits, so it blows up

2020-07-09 22:02

there we go. pretty simple in the end, accepted a loss of one bit of precision the line step calc to avoid three left shifts, all of which might overflow. it’ll take a keener eye than mine to spot any material difference

2020-07-11 00:46

it’s so soothing I love it

originally posted on twitter at: https://twitter.com/robn/status/1280075070589698050