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SAA5050 Character Rounding #98898 03/30/15 10:30 AM
Joined: Apr 2012 Posts: 340 Likes: 60 UK Pernod OP Senior Member
OP Pernod Senior Member Joined: Apr 2012 Posts: 340 Likes: 60 UK	I see the internal ROM is stored as an array of 8bit values, where the rightmost 5 bits represent the actual characters to form a 5x9 grid. Is this an accurate representation of the ROM, or don't we know? To implement the rounding I intend to copy the character into an array of 16bit values to form a 10x18 grid, formed by expanding each original bit to 4 bits, then adding subpixels to any diagonal. ie. . # -> . . # # -> . . # # # . -> . . # # -> . # # # . . -> # # . . -> # # # . . . -> # # . . -> # # . . Not sure yet how this will affect double height characters but will find out when this is in. Is this the correct way to implement this, any comments? Last edited by Pernod; 03/30/15 10:31 AM. BBC Model B, ATPL Sidewise, Acorn Speech, 2xWatford Floppy Drives, AMX Mouse, Viglen case, etc.

Re: SAA5050 Character Rounding Pernod #98987 04/03/15 06:52 PM
Joined: Apr 2012 Posts: 340 Likes: 60 UK Pernod OP Senior Member
OP Pernod Senior Member Joined: Apr 2012 Posts: 340 Likes: 60 UK	I'm in the process of making major changes to saa5050.c. I originally intended to simply implement the character rounding but soon became obvious more was required to get this character generator into shape. The data in the 'hand made' ROM dump also contained the graphics characters which are not required, they can be generated internally so I'll be implementing the 'graphics generator'. I've removed the graphics from the saa5050 and saa5052 'dumps' and also created 'dumps' for all other character sets 5051, 5053, etc. for completeness. The saa5050 dump contained some erroneous characters which I've also fixed. Some control codes only take effect at the next character and affected control codes are now handled correctly. At the moment I need to convert a pixel map of '00010101' (UINT8) to '0000001100110011' (UINT16), each pixel is doubled in width. Anyone suggest a simply way of doing this, or should I check each bit separately? BBC Model B, ATPL Sidewise, Acorn Speech, 2xWatford Floppy Drives, AMX Mouse, Viglen case, etc.

Re: SAA5050 Character Rounding

Pernod #98988 04/03/15 07:00 PM

Joined: Mar 2001

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R. Belmont Online Content

Very Senior Member

R. Belmont

Very Senior Member

Joined: Mar 2001

Posts: 17,178

Likes: 211

USA

For a character generator inner loop, I'd suggest the classic unroll-o-matic:

Code

*dst++ = (src & 0x80) ? 0xffff : 0;
*dst++ = (src & 0x80) ? 0xffff : 0;
*dst++ = (src & 0x40) ? 0xffff : 0;
*dst++ = (src & 0x40) ? 0xffff : 0;
*dst++ = (src & 0x20) ? 0xffff : 0;
*dst++ = (src & 0x20) ? 0xffff : 0;
*dst++ = (src & 0x10) ? 0xffff : 0;
*dst++ = (src & 0x10) ? 0xffff : 0;
*dst++ = (src & 0x08) ? 0xffff : 0;
*dst++ = (src & 0x08) ? 0xffff : 0;
*dst++ = (src & 0x04) ? 0xffff : 0;
*dst++ = (src & 0x04) ? 0xffff : 0;
*dst++ = (src & 0x02) ? 0xffff : 0;
*dst++ = (src & 0x02) ? 0xffff : 0;
*dst++ = (src & 0x01) ? 0xffff : 0;
*dst++ = (src & 0x01) ? 0xffff : 0;

Re: SAA5050 Character Rounding Pernod #98992 04/04/15 09:51 AM
Joined: Jun 2001 Posts: 519 Likes: 32 somewhere else entirely O Olivier Galibert Senior Member
Olivier Galibert Senior Member O Joined: Jun 2001 Posts: 519 Likes: 32 somewhere else entirely	Originally Posted by Pernod At the moment I need to convert a pixel map of '00010101' (UINT8) to '0000001100110011' (UINT16), each pixel is doubled in width. Anyone suggest a simply way of doing this, or should I check each bit separately? https://graphics.stanford.edu/~seander/bithacks.html Check "Interleave bits by Binary Magic Numbers" OG.

Re: SAA5050 Character Rounding Pernod #99058 04/07/15 09:37 PM
Joined: Apr 2012 Posts: 340 Likes: 60 UK Pernod OP Senior Member
OP Pernod Senior Member Joined: Apr 2012 Posts: 340 Likes: 60 UK	A quick update... the graphics generator is implemented and working in bbcb, ROM characters are unrolled in a similar way to RB's suggestion (not sure how the Binary Magic Numbers would've helped), still to fix character rounding. Also tested poly1, p2000t, abc80x and no obvious side effects noticed so far BBC Model B, ATPL Sidewise, Acorn Speech, 2xWatford Floppy Drives, AMX Mouse, Viglen case, etc.

Re: SAA5050 Character Rounding Pernod #99062 04/07/15 10:13 PM
Joined: Mar 2006 Posts: 1,079 Likes: 6 PA, USA L Lord Nightmare Very Senior Member
Lord Nightmare Very Senior Member L Joined: Mar 2006 Posts: 1,079 Likes: 6 PA, USA	character 'rounding': is this similar to the character 'stretching' done in the vt100/rainbow, where each pixel is an OR of its own source rom value and the rom value of the pixel to its left? i.e. from the font rom the characters look like: Code Character: 62 ........ X....... X....... X.XXXX.. XX....X. X.....X. XX....X. X.XXXX.. ........ ........ while after the stretching right before being drawn to screen, characters looks like: Code Character: 62 ........ XX...... XX...... XXXXXXX. XXX...XX XX....XX XXX...XX XXXXXXX. ........ ........ The reason the gaps exist at all in the rom is because the double-width font mode on the vt100/rainbow makes the gap visible for one pixel. I.e. the char stretch is done right before being sent to the display, so the doublewide char going into the stretch circuit looks like: Code Character: 62 ................ XX.............. XX.............. XX..XXXXXXXX.... XXXX........XX.. XX..........XX.. XXXX........XX.. XX..XXXXXXXX.... ................ ................ and ends up like: Code Character: 62 ................ XXX............. XXX............. XXX.XXXXXXXXX... XXXXX.......XXX. XXX.........XXX. XXXXX.......XXX. XXX.XXXXXXXXX... ................ ................ LN "When life gives you zombies... CHA-CHIK! ...you make zombie-ade!"

Re: SAA5050 Character Rounding Lord Nightmare #99063 04/07/15 10:35 PM
Joined: Apr 2012 Posts: 340 Likes: 60 UK Pernod OP Senior Member
OP Pernod Senior Member Joined: Apr 2012 Posts: 340 Likes: 60 UK	Originally Posted by Lord Nightmare character 'rounding': is this similar to the character 'stretching' done in the vt100/rainbow, where each pixel is an OR of its own source rom value and the rom value of the pixel to its left? No, definitely different. The ROM contains a 5x9 pixel map: (Done) Code Character: 62 X.... X.... XXXX. X...X X...X X...X XXXX. ..... ..... which is then mapped to a 10x18 pixel map by doubling in both directions: (Done) Code Character: 62 XX........ XX........ XX........ XX........ XXXXXXXX.. XXXXXXXX.. XX......XX XX......XX XX......XX XX......XX XX......XX XX......XX XXXXXXXX.. XXXXXXXX.. .......... .......... .......... .......... then dot information of two rows is compared to detect any diagonal and fill in a dot to round it: (TODO) Code Character: 62 XX........ XX........ XX........ XX........ XXXXXXXX.. XXXXXXXXX. XX.....XXX XX......XX XX......XX XX......XX XX......XX XX.....XXX XXXXXXXXX. XXXXXXXX.. .......... .......... .......... .......... The method is a little more complex for double height characters, but we'll look at that later. BBC Model B, ATPL Sidewise, Acorn Speech, 2xWatford Floppy Drives, AMX Mouse, Viglen case, etc.

Re: SAA5050 Character Rounding Pernod #99064 04/07/15 11:45 PM
Joined: Mar 2006 Posts: 1,079 Likes: 6 PA, USA L Lord Nightmare Very Senior Member
Lord Nightmare Very Senior Member L Joined: Mar 2006 Posts: 1,079 Likes: 6 PA, USA	so the rounding isn't something 'simple' like EPX/scale2x, its somewhat more complex? (maybe with a 3x3 '9-cell' kernel instead of a + shaped '5-cell' kernel like EPX/scale2x uses?) Is the rounding algorithm documented anywhere? LN "When life gives you zombies... CHA-CHIK! ...you make zombie-ade!"

Re: SAA5050 Character Rounding Pernod #99065 04/08/15 04:17 AM
Joined: Jan 2006 Posts: 3,691 Trondheim, Norway etabeta78 Very Senior Member
etabeta78 Very Senior Member Joined: Jan 2006 Posts: 3,691 Trondheim, Norway	Originally Posted by Pernod (not sure how the Binary Magic Numbers would've helped) by giving you an example implementation, if you needed one see https://graphics.stanford.edu/~seander/bithacks.html#InterleaveTableObvious which applies in your case with x=y

Re: SAA5050 Character Rounding Pernod #99080 04/08/15 06:20 PM
Joined: Mar 2006 Posts: 1,079 Likes: 6 PA, USA L Lord Nightmare Very Senior Member
Lord Nightmare Very Senior Member L Joined: Mar 2006 Posts: 1,079 Likes: 6 PA, USA	hmm. if rounding is only diagonals, here's one GUESSED possibility: 1. double the character size 2. for every pixel: Code /* A.B .N. C.D / if ( (N == 0) && ( ((A == D == 1) && (B == C == 0)) \|\| ((A == D == 0) && (B == C == 1)) ) ) N = 1; This is applied to all pixels at once, hence a pixel set to 1 by this equation doesn't count for calculations of other pixels? This seems somewhat complex to implement in hardware, though, unless it is done by a circuit during output with lookback of the previous 2 lines. Edit: easier code: Code / A.B .N. C.D / if ( (N == 0) && ((A == D) && (B == C) && (A != B)) ) N = 1; LN Last edited by Lord Nightmare; 04/08/15 06:22 PM. Reason: better code "When life gives you zombies... CHA-CHIK!* ...you make zombie-ade!"

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