World: r3wp

it's the offset from the baseline

The ``charpath'' operator extracts the graphic shapes of its string 
operand and appends them to the current path in the graphic state. 
These shapes can then be processed by other PostScript operators. 
To get the actual size of the area touched by a character a simple 
approach is

	gsave
	newpath
	0 0 moveto
	(X) false charpath flattenpath pathbbox
	grestore


This code places four numbers on the stack, representing the coordinates 
of the lower left and upper right corners of the bounding box enclosing 
the character ``X'' rendered with the current point at (0,0). Leaving 
the flattenpath out will cause it to be less accurate, but it will 
take up less memory and be faster.

how do I call it again, with /fontsize or fontsize?

tried that one, couldn't get it to work.

though not in that form

faq: http://www.postscript.org/FAQs/language/node67.html

nope, that doesn't work either

what do you mean it doesn't work?

I get a postscript error.

Got the font size to work, but it doesn't take the baseline into 
account.

time for bed... Geomol can take over in the morning. :-)

aren't you both in the same timezone?

yes

yes! got grahams method working now. thanks.

it also helps better top alignment

Geomol, you may find my changes here:

http://hmkdesign.dk/rebol/postscript.r

The changes are:


- Stores the font size inside PS every time a new font is selected. 
This is not used however, but perhaps is useful in the future.

- Added bottom, middle and top alignment for TEXT. Similarly to how 
you specify a size for LEFT, CENTER and RIGHT, you can enter a size 
for TOP, MIDDLE and BOTTOM:

Some text
 center 400 middle 200

Both sets are optional. The default alignment is LEFT and BOTTOM.

My changes are marked HMK in the source. I hope it is of use.

now it would be nice with some form of margin management

I was looking at the postscript operator STRINGWIDTH. It seems to 
be able to take two arguments, for x and y width. Are you using that?

I use it only for X. The Y component is not a height, but something 
else.

it has something to do with offsetting from the glyph origin, I think

but now I have margin working too. it was simple to add.

updated source code for download

allegedly the method graham describes is not very efficient, but 
it works accurately and that's what I want.

Yes, the y width seems to be for vertical writing, like in chinese.

I'll take a look at your changes...

moved the source to http://hmkdesign.dk/rebol/postscript/postscript.r

example of adjustments: http://hmkdesign.dk/rebol/postscript/testsheet.ps

(table is my own component, not part of postscript.r :-))

Geomol, there is some code duplication in there. Perhaps it can be 
optimized?

seems it's still not accurate :-( it still calculates the baseline 
incorrectly when using letters like "g"

so if the bounding box does that for a single word, we need to use 
all chars in the alphabet to calculate the height correctly for any 
char combination. it does not do that right now

If vertical position should be in the dialect, I think, it should 
be based on a real postscript feature. If such a thing isn't found 
in postscript, it should be implemented on a higher level, shouldn't 
it?

The problem is to get the height accurately for all glyphs for a 
font (I just got that now). Some fonts have very high tops and very 
low bottoms and you want that to work for any font and letter combination 
we throw at it. it would be harder to get that information inside 
REBOL than inside postscript.

I got it rendered now so that the vertical position is at least consistent 
now, but the font is offset a few points too far down. I don't know 
why yet, but it's probably the baseline again.

there is another method which is to get the bbox information from 
the font metric file itself. it's much faster, since it's just lookup, 
but I couldn't find an example of how to read it.

so my current method is Graham's, except for calculating the entire 
alphabet. we should probably work on getting that information from 
the font metric file instead.

In Adobe documentation, they operate with "character origin", which 
is the baseline, I think. If you do:
40 50 moveto (ABC) show
, the origin of the A letter is at coordinate (40, 50).

So it doesn't matter, how high the font is.

you still need to know the size of the bbox, don't you?

A vertical positioning would be a simple calculation. Say, you want 
the baseline to be positioned at the middle of a 300 point high box 
starting at pos (100, 100). You then start by putting text at coord 
(100, 250).

The y coord is 300 / 2 plus the 100 = 250.

that assumes that the text is rendered from its own center point. 
it isn't, is it?

If you wanna build a table, you calculate the position of each line 
like this, and send the precise coords to the postscript dialect. 
It would probably be best to build a new dialect on top of the postscript 
one, and in that dialect handle the calculations.

No, text is rendered from the "character origin" (the baseline), 
which can be different than the center of the text. This should probably 
be taken care of, if needed. hm

the table is a different matter :-) it's already done, not yet as 
a dialect though. I will build one later.

The baseline problem is the one I'm hunting a solution for. About 
the font metrics, the bbox for the whole font is stored in FontBBox 
in the font dictionary.

If your goal is, that the text is completely centered vertically, 
then you have a problem. Because how do you know, what characters 
to be written? If there is no 'g' in the word, you need to position 
it a bit lower, than if you had 'g' in the text, for it to be completely 
middle aligned.

that you solve by calculating the bbox for the entire alphabet instead 
of just the words you write

this way the height will be constant