Beebem Mode 7 glitch

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guesser
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Re: Beebem Mode 7 glitch

Post by guesser » Thu Jul 05, 2018 10:27 pm

colonel32 wrote:
Thu Jul 05, 2018 10:21 pm
Understood. Easily accommodated at my end, and of course ZX Net works a treat ;)
I'll mention these issues to Simon and see if he wants me to patch them up for him. Obviously I'd recommend using my own editor instead if I wasn't so modest :lol:
Does this forum have a plug tax? it was always 75p and a packet of rolos on comp.sys.sinclair :wink:
A web based teletext editor which can export as Mode 7 screen memory: https://zxnet.co.uk/teletext/editor

colonel32
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Re: Beebem Mode 7 glitch

Post by colonel32 » Thu Jul 12, 2018 3:30 pm

Cheers, guesser.

On another note, I'm scratching my head over this table from the 1976 teletext spec.

I thought I understood the spec perfectly until I saw this. What are they trying to convey by includes/excludes RED/GREEN/BLUE? Is it just a convoluted way of saying colours don't set themselves?

Image
Last edited by colonel32 on Thu Jul 12, 2018 3:33 pm, edited 1 time in total.

guesser
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Re: Beebem Mode 7 glitch

Post by guesser » Thu Jul 12, 2018 4:07 pm

That just seems to be a really convoluted way of saying which RGB lines will be activated by each colour control codes.
A web based teletext editor which can export as Mode 7 screen memory: https://zxnet.co.uk/teletext/editor

colonel32
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Re: Beebem Mode 7 glitch

Post by colonel32 » Thu Jul 12, 2018 8:17 pm

Cheers! What about this one here, also from the 1976 spec (italics mine):
3.1.6 Double Height
[...]
A receiver responding to one or more occurences of the Double Height mode in Row 'R' will operate as otherwise during that Row except that in every Character Rectangle during the Double Height mode only the upper half of what would otherwise have been displayed is displayed, stretched vertically to fill the rectangle. On Row 'R+1' the corresponding lower half of each of these is similarly displayed. The remaining Character Rectangles of Row 'R+1' are to be displayed as unboxed spaces of the same Background colour as the corresponding Character Rectangles of Row 'R'.
To me this implies double-height backgrounds only get copied down after Double Height 0x8D, and stop getting copied down after Normal Height 0x8C. But neither edit.tf, zxnet nor Richard's telstar.bbc do that - they copy everything down if there's at least one Double Height 0x8D.

At the moment my own parser doesn't agree with this test page or anybody else, which is what flagged this up (as I was coincidentally following my own interpretation of that paragraph, before I reread it closely!) DH Doesn't get set till column 2, and gets applied in column 3:

Image
Last edited by colonel32 on Thu Jul 12, 2018 8:37 pm, edited 6 times in total.

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ctr
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Re: Beebem Mode 7 glitch

Post by ctr » Thu Jul 12, 2018 8:58 pm

colonel32 wrote:
Thu Jul 12, 2018 8:17 pm
To me this implies double-height backgrounds only get copied down after Double Height 0x8D, and stop getting copied down after Normal Height 0x8C.
I read it the other way.

"The remaining Character Rectangles" refers to the character rectangles that aren't in double height. So the background is copied for these. The background is also copied for the double height characters, so it is copied for the entire row.

And this makes sense functionally. If you are only broadcasting the first row of the pair it is reasonable to take the background colour for the second row from the first.

(Of course, this is all moot in Mode 7 because both rows are specified, double height or not.)

colonel32
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Re: Beebem Mode 7 glitch

Post by colonel32 » Fri Jul 13, 2018 3:15 am

ctr wrote:
Thu Jul 12, 2018 8:58 pm
I read it the other way.
I think I'm convinced, thanks.

I've now got this test page rendering properly:

Image

Soruk
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Re: Beebem Mode 7 glitch

Post by Soruk » Sat Jul 14, 2018 9:05 pm

Yay - another test page rendering as it should in Brandy.
Last edited by Soruk on Mon Jul 16, 2018 3:55 pm, edited 1 time in total.

guesser
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Re: Beebem Mode 7 glitch

Post by guesser » Sun Jul 15, 2018 10:14 am

again, it's made less ambiguous in the current spec:
When double height (or double size) characters are used on a given row, the row below normal height characters on that row is displayed with the same local background colour and no foreground data.
A web based teletext editor which can export as Mode 7 screen memory: https://zxnet.co.uk/teletext/editor

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