mtext adj= wrong with several las= (PR#7188)

joehl@gmx.de wrote:

Dear all, 

Our quite basic function mtext() does wrong adjustments in some parameter
configurations. This gets obvious when using multi line texts: There is no
way to properly adjust text perpendicular to axis 2, for example.

Best

Jens Oehlschl?gel

m <- matrix(1:9, 3)
colnames(m) <- c("several\nlines", "several\nlines", "several\nlines")

par(mfrow=c(2,2))
barplot(m, horiz=TRUE, axes=FALSE, axisnames=FALSE, main="las=0 adj=0.5 is
fine")
mtext(colnames(m), 2, at=seq(0.5+0.2, by=1+0.2, length=3), las=0, adj=0.5)
barplot(m, horiz=TRUE, axes=FALSE, axisnames=FALSE, main="las=0 adj=1 is
different")
mtext(colnames(m), 2, at=seq(0.5+0.2, by=1+0.2, length=3), las=0, adj=1)
barplot(m, horiz=TRUE, axes=FALSE, axisnames=FALSE, main="las=1 adj=0.5 is
NOT fine")
mtext(colnames(m), 2, at=seq(0.5+0.2, by=1+0.2, length=3), las=1, adj=0.5)
barplot(m, horiz=TRUE, axes=FALSE, axisnames=FALSE, main="at las=1, adj=1
works the wrong direction", sub="no way to get adj=c(1, 0.5) with las=1 (or
2)")
mtext(colnames(m), 2, at=seq(0.5+0.2, by=1+0.2, length=3), las=1, adj=1)
par(mfrow=c(1,1))

Left / right adjustemnt seems to be perfectly OK.
The thing that matters is centering "several lines" to the specified 
("at=") location.
In fact, mtext() is not centering but bottom-aligning by adding a 
negative distance that looks OK for one line in the default font size, 
but not in most other cases.

Hence this is the same as Paul Murrell's PR#1659 ("mtext() alignment of 
perpendicular text"). Fixing this, and/or improving mtext()'s "adj" 
argument to accept 2 dimensions is desirable, but might be not that 
easy... I'll take a look during the next days, but nothing promised.

Uwe Ligges
Having looked into the code, there are three possible solution (all with
some drawbacks) I can see. Well, the current argument "adj" becomes
"xadj" in the C sources (graphics.c, GMtext), and "yadj" is set to 0. 
Hence the ugly hard coded LineBias of 0.3.

Solutions
=========
1: Hardcode "yadj" to 0.5 and remove all those 0.3 biases. Looks good 
for axes, but it might break some code --> bad.
On the other hand, GMMathText has hardcoded yadj=0.5. Is there a problem 
with some special devices? Or any other reason not to center stuff using 
"adj=0.5"?

2: Allow the typical 2-value adj, take the first as xadj, the second one
as yadj. This might break some code, because currently adj of
arbitrary length (!=0) is allowed and recycled.

3: Invent an argument "padj" for mtext() that represents adjustment
*p*erpendicular to the text direction and gets mapped to "yadj" in
GMtext. In that case the hardcoded 0.3 bias mentioned above can be
removed. The question is whether to set the default to 0.5 (will still
break code, but easily to fix by setting padj to 0).

I'd like to propose the third solution and would be happy to provide a
patch of GMText, including corresponding patches to GMMathText, as well 
as mtext(), title() and axis() (and their inderlying do_* components).

Are there any objections? Any reasons not to do it?

Uwe Ligges

version
        _              
platform i386-pc-mingw32
arch     i386           
os       mingw32        
system   i386, mingw32  
status                  
major    1              
minor    9.1            
year     2004           
month    06             
day      21             
language R   

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mtext adj= wrong with several las= (PR#7188)

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