What styling does the 6502 terp support?

[dstelzer]

I don't actually know what's supported and what's not. Invisible divs should be, if possible. Beyond that…what can a C64 do, formatting-wise?

[dstelzer]

It looks like it generates four character sets: normal, bold, italic, bold italic. Those are the only styles it recognizes.

For invisibility, it looks like setting stflag (status flag) to $FF turns off output. So if I can figure out where the CSS is parsed, I can flag invisibility there. Then, when entering a div, check for that flag; if found, set the stflag. When leaving that div, unset it? Something like that?

[dstelzer]

I think a better option will be to test a bit in the style register. If I use bit 6, a BIT instruction will do nicely.

[susan-davis]

Oh. Oh, my. If we have four character sets to choose from, the Commodore programmer in me wants to be able to choose to throw either bold or italic overboard, and have two whole character sets lying around for extra Unicode characters or for full-custom graphics. (Or both, and have 768 characters in my palette for drawing graphics. Or to claw back 768 bytes to squeeze in a game that almost fits but doesn't.) Do we really have the interrupt tricks in place to actually use four different character sets on screen at the same time?

[dstelzer]

That I don't know. But this is how the style is set:

io_mstyle
	; input a = style bits

	.(
	pha
	jsr	io_mflush
	pla
	lsr
	and	#3
	tax
	lda	palette,x
	sta	currfg
	rts
palette
	.byt	$0	; normal
	.byt	$b	; bold
	.byt	$6	; italic
	.byt	$e	; italic bold
	.)

And this is how it's used:

	lda	1
	pha
	lda	#$35
	sta	1
loop
	lda	wrapbuf,x
	sta	(ioline),y
	lda	currfg
	sta	(iocram),y
	iny
	inx
	cpx	wrappos
	bne	loop

	pla
	sta	1

(Both in c64_frontend.s.)

So it looks like currfg (the foreground palette) is set to $0 for normal, $6 for italic, $B for bold, and $E for italic bold; then it's stored into each character's portion of iocram.

[dstelzer]

Now that I've actually tried this out in practice: normal text is black-on-white, bold is gray-on-white, italic is blue-on-white, and bold italic is cyan-on-white.

This is probably obvious to the actual C64-users, but I have very little experience with this…

[dstelzer]

Or rather, looking at some actual C64 documentation, normal text ($0) is black, italic ($6) is blue, bold ($B) is "dark gray/gray 1", and bold italic ($E) is light blue. Orange ($8) is also used for the cursor.

With almost 256 printable characters available in the Å-machine (since the C64 terp uses some of the 33 control characters for things like progress bar pieces), there just isn't memory available—as far as I can tell—for multiple actual character sets. So color makes sense. It would be nice if it could support at least one additional color beyond "bold" and "italic", though, for links.

[dstelzer]

Reverse-video style is the obvious next choice. It goes in the lowest bit of the style register, so supporting it would be as easy as removing that LSR instruction and expanding the table. (And, well…making the CSS parser handle it properly. But (reverse) would work even without that.)

It wouldn't be true reverse-video, just like it's not true bold or italics. But the current rule seems to be that bold is a lighter color, and italics are blue. So reverse could be red, reverse bold orange. What would reverse italic and reverse bold italic be? Purple and pink, I suppose would be logical? The green seems potentially hard to read against the white background.

[dstelzer]

Reverse mode added in #101 . Invisible divs not yet supported.