At 10:38 PM 8/24/2002 -0400, you wrote:
Ok, I've finally seen what's being drawn. Glenn, can you
explain what I'm seeing? There've been a few revisions to
the demo, and I haven't been keeping track.
There are two kernels, an odd and an even line kernel. If you run the demo
on a real VCS and toggle the select switch you'll see the system go from
showing the odd kernel, the even kernel, and then the interlaced kernel.
When interlaced, the odd and even alternate, naturally. The even lines
appear above the odd ones.
bk pf
Zone 1 E Blue Red
Zone 1 O Red White
When you select through the noninterlaced kernels, Zone 1 shows solid
blue/red or solid red/white, then a mixture in interlace that blends into a
magenta and pink on the PF.
Zone 2 E Black Black (i.e. blank)
Zone 2 O Red White
Zone 3 E Blue Red
Zone 3 O Black Black (i.e. blank)
When you select through the noninterlaced kernels, zone 2 and zone 3 will
alternate being displayed (solid) and when interlaced, they will show up
flickery with lines in between them.
So these top scanlines are a good testbed for interlace.
Zone 4 E Red White
Zone 4 O Red White
Zone 5 E Blue Red
Zone 5 O Blue Red
These two zones are the "control". They will appear the same whether or
not interlace happens, but obviously when interlacing, each scanline will
alternately flicker.
Zone 5 E Red White
Zone 5 O Black Black
Zone 6 E Black Black
Zone 6 O Blue Red
These two zones show what a single scanline looks like with interlace, i.e.
30hz flicker.
Zone 7 E 00+4
Zone 7 O 02+4
In this zone each kernel cycles through colors +4 at a time, offset by
2. This has the effect of one kernel being slightly brighter than the
other when you toggle through the noninterlaced modes. But in interlaced
mode they fill in eachother for a full smooth color gradient across all 128
colors in the same vertical zone that would normally only cover 64 lines.
In Zone8 I create a diagonal line using playfield by doing something like this:
eo000000
00eo0000
0000eo00
000000eo
e = even
o = odd
So on the individual kernels I am skipping a pixel.
In noninterlaced you'll see these gaps from the skips. In interlaced, the
gaps get filled in with a somewhat flickery but high-vertical-res diagonal
line.
In the screengrab I merged the fields so you don't get to see the flicker.
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