Hezekiah M. Carty wrote:
> On Wed, Jun 3, 2009 at 3:40 PM, Hezekiah M. Carty<hca...@atmos.umd.edu> wrote:
>> While writing the Cairo backend for plarc, I am having some trouble
>> getting the transformation from world coordinates to Cairo coordinates
>> correct.
>
> I have attached a patch which implements the plarc function, adds
> Cairo-specific support for arc outlines and fills, and updates example
> 3 to use plarc for the polar plot circles. It is my hope that someone
> with more experience with the PLplot internals can point out what I am
> doing wrong with the scaling of the coordinates. The implementation
> is still incomplete as plot-device-accelerated plarc calls are not
> added to the plot buffer yet. It is complete enough to compare the
> "proper" results (ex. using the xwin device) with the incorrectly
> scaled results (ex. using the xcairo device).
>
>>From what I understand, the problem is in src/plarc.c in the c_plarc
> function, somewhere between lines 128 and 144 where arc-capable
> devices are handled. The Cairo rendering function is in
> drivers/cairo.c and is called arc().
>
> Thank you for any insight you can provide on this.
What is missing is that coordinates from plline(), etc... are run
through a final transformation function called difilt() in plcore.c.
The best solution I was able to come up with is something like this:
PLINT xscl[2], yscl[2];
PLINT clpxmi, clpxma, clpymi, clpyma;
arc_struct *arc_info;
if (plsc->dev_arc) {
/* If the driver can handle arcs, let it */
arc_info = (arc_struct *) malloc((size_t) sizeof(arc_struct));
xscl[0] = plP_wcpcx(x-a);
xscl[1] = plP_wcpcx(x+a);
yscl[0] = plP_wcpcy(y-b);
yscl[1] = plP_wcpcy(y+b);
difilt(xscl,yscl,2,&clpxmi,&clpxma,&clpymi,&clpyma);
arc_info->x = 0.5 * (xscl[1] + xscl[0]);
arc_info->y = 0.5 * (yscl[1] + yscl[0]);
arc_info->a = 0.5 * (xscl[1] - xscl[0]);
arc_info->b = 0.5 * (yscl[1] - yscl[0]);
I don't think this will play nicely with arbitrary plot rotations
though, which I think that we support.
Also, you should add a comment about what the rotation parameters does.
best,
-Hazen
------------------------------------------------------------------------------
OpenSolaris 2009.06 is a cutting edge operating system for enterprises
looking to deploy the next generation of Solaris that includes the latest
innovations from Sun and the OpenSource community. Download a copy and
enjoy capabilities such as Networking, Storage and Virtualization.
Go to: http://p.sf.net/sfu/opensolaris-get
_______________________________________________
Plplot-devel mailing list
Plplot-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/plplot-devel
