Re: Adding an _arc() terminal entry

[Christoph B. <us...@be...>]

Am 18.04.2013 22:40, schrieb Ethan A Merritt:
> On Thursday, April 18, 2013 12:06:59 pm Christoph Bersch wrote:
>>
>> * I would suggest, that the information, whether clipping is necessary,
>> and to which rectangle it should be clipped is provided by a
>> terminal-independent function.
>
> The current clipping area is maintained in the global structure
>    gadgets.h:extern BoundingBox *clip_area; /* Current clipping box */

Yes, I saw this, but didn't know if this information was supposed to be 
transparent to the terminal drivers.

>> In the current implementation
>> the circle object is useless for marking something around the graph
>> boundary (could just be a single dot on the border).
>
> Not really.  You just have to specify the position in screen, rather
> than plot, coordinates.  You wouldn't normally specify the graph
> boundary in plot coordinates anyhow so I don't see this as much of a
> restriction.  It is true that the most obvious way to position
> something on the graph boundary is to use graph coordinates
>     set obj 1 at graph 0, graph 1
> and currently the code in graphics.c would set the corresponding
> clip area to the graph boundary.  Perhaps it shouldn't?  Or perhaps
> that would be where your proposed clipping flag would come in?

Yes, in my case it was something like:

set xrange[0:10]
set yrange[-1.2:1.2]
set object circle at graph 0, first 1 radius 0.1
plot cos(x)

And specifying this circle center with screen coordinates is somewhat 
fiddly.
Also if one plots with circle

>> This might also be
>> implemented as a new value for 'set clip' and could also affect all
>> other objects.
>
> The same clipping area and clipping primitives are used for all
> objects.  The clipping of filled curves is a partial exception,
> since it gets very complicated to determine the correct clipping
> for a filled curves whose vertices are off the edge of the canvas.
>
>> As another thing I would suggest two distinct terminal entries _arc()
>> and filledarc().
>>
>> I'm looking forward to your comments and suggestions,
>
> I suggest that before investing a lot of time in this you first
> dummy up a bit of terminal-specific output and compare it to the
> result of the generic code in do_arc().  You might be surprised
> at how much alike they look.  I originally coded up a postscript
> specific term->arc routine that used the PS Level 2 arc function.
> But the result was not notably better than the generic function
> so I abandoned the idea.  That was before the cairo terminals
> were added, however, so I didn't do the comparison for those.

I already have some code snippets for the cairo, Postscript and SVG 
terminals. You are right, there is hardly any difference, but I liked 
the idea of having an own terminal entries for graphic primitives like 
the circle :-)

Thank you for you comments,
Christoph