tlr wrote:My experience is that colors look slightly different depending on which type they are. Background colors are slightly off from the same border colors on the machines I have seen. Might be just due to some kind of AEC like effect superimposed when graphics is being redered as opposed to border.
JonBrawn wrote:Rest assured, I shall not be deliberately trying to replicate that in my FPGA... having said which, I also haven't intentionally tried to implement the infamous jail bars, and yet they turned up to the party uninvited. What is "AEC"?
AEC ^= Address Enable Control. This is a signal on the C64/C128 mainboard which is used by VIC-II to tri-state the address bus of the CPU.
There exists a visible correlation between AEC and a modulation on luma. So-called "luma-fix" units use AEC together with PHI0 to compensate that luma modulation and get a more even appearance on screen.
Several bus signals cause the luma to slightly decrease - see this picture (much exaggerated for demonstration of course). In the vic20 there is probably similar stuff happening.
I'm just a Software Guy who has no Idea how the Hardware works. Don't listen to me.
groepaz wrote: ↑Fri Oct 14, 2022 11:25 am
Several bus signals cause the luma to slightly decrease - see this picture (much exaggerated for demonstration of course). In the vic20 there is probably similar stuff happening.
Come to think of it, I believe border color in the screen area using MC mode is different from BG color i MC mode side by side so it might be a different effect. Could be 8 color pixels vs 16 color pixels perhaps. Not sure, was a long time ago, but keep an eye our for it.
groepaz wrote:Several bus signals cause the luma to slightly decrease - see this picture (much exaggerated for demonstration of course). In the vic20 there is probably similar stuff happening.
tlr wrote:Come to think of it, I believe border color in the screen area using MC mode is different from BG color i MC mode side by side so it might be a different effect. Could be 8 color pixels vs 16 color pixels perhaps. Not sure, was a long time ago, but keep an eye our for it.
There's a 0% chance though, that the non-consideration of those effects will stop VIC-20 programs from working - regardless whether VICE or say, Jon's FPGA replacement were involved.
At best, pixel artists could have a legitimate interest in mixed colors being displayed correctly in e.g. fcbpaint or MINIPAINT in emulation, and that there are no negative surprises when the picture is then shown on real hardware.
