Sunday 9 November 2014

More work on proportional fonts

I have done a bit more work on the unicode text display programme.

The following screen-shot is completely generated by the programme, in contrast to the screen-shot in the previous post where I manually populated the screen memory with the tiles and kerning adjustments.

The Unicode string used to feed the program is:

       .word 'H,'e,'l,'l,'o,$20,'W,'o,'r,'l,'d
       .word $000d
       .word $05d4,$05d3,$05d2,$05d1,$05d0
       .word $000d
       .word 'g,'a,'r,'y,$20,'j,'u,'p,'i,'t,'e,'r
       .word $000d       
       .word 0

Character $20 is of course space, and the $05xx characters are some Hebrew glyphs I threw in just to show that we are not limited to latin characters.

So, how did it turn out?

The screen shot is actual size so that there is hopefully no strange things going on in terms of smoothing of the zoomed image.

The slight green sheen is an artefact of the C65GS VNC server which sends pixels using a 3x3x2 colour cube, and so suffers some colour distortion.  This doesn't need fixing since it is purely a VNC artefact.

We still have the kerning glitch, because the VIC-IV isn't honouring the least significant bit of the kerning field, so H and W are followed by one more blank pixel than they should.  This is on my list to fix in the FPGA programme.  I'll likely rearrange the bits so that the kerning bits are all adjacent, instead of spread between two different bytes (one of which is clearly not being read properly).

The programme has, however, faithfully rendered the first line of Latin and Hebrew Unicode characters, including H and W that are two tiles wide.

It also handles the carriage-returns, however, it doesn't correctly calculate how many rows of characters are needed, nor does it allow for reducing the height of character rows to provide correct line spacing.  This will require implementing the remaining hardware support for this in the VIC-IV.

Also, in the character rows that don't contain active non-blank glyphs, it isn't putting a blank tile there, nor is it adjusting the width of each to kern them to the correct width, so there is rubbish which is wider than the actual text on the 2nd and 3rd rows of each line of output.  This won't be too hard to fix, as it is just a software issue.

Finally, the third row is really messed up, because the line of characters that are drawing the under-hanging pixels are being written over the main row, instead of being written into the next row down.  This shouldn't be too hard to fix either, as it is just a software issue.

Also, it would be nice if the routine cleared the remainder of the screen, but that's really just icing on the cake.

So for now we have a nice bit of progress, and I might take a look at fixing the kerning and rows of junk bugs next.

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