nanogui: Thread: GrArc() function

Hello,

I am doing my best to annoy myself figuting out how the GrArc() function
is supposed to be used.

So far, x/y/rx/ry/ are easy enough.

Fiddling with ax, ay, bx, by does nt reveal anything intuitive.

Can someone please explain how to use them?

Thanks!

-robert

void  GrArc( GR_DRAW_ID id, GR_GC_ID gc,
    GR_COORD x, GR_COORD y,
    GR_SIZE rx, GR_SIZE ry,
    GR_COORD ax, GR_COORD ay,
    GR_COORD bx, GR_COORD by,
    int type)

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On Wed, 29 Nov 2000, Robert Hartley wrote:
> I am doing my best to annoy myself figuting out how the GrArc() function
> is supposed to be used.

Ah, it appears that Greg never included the API documentation I wrote
several months ago... You can find a copy at:
ftp://ftp.linuxhacker.org/pub/nanogui/nano-X-API.tar.gz

Should I send you the patch again, Greg?

Not sure how much it'll help, but this is the GrArc() entry:

GrArc ()

void        GrArc                           (GR_DRAW_ID id,
                                             GR_GC_ID gc,
                                             GR_COORD x,
                                             GR_COORD y,
                                             GR_SIZE rx,
                                             GR_SIZE ry,
                                             GR_COORD ax,
                                             GR_COORD ay,
                                             GR_COORD bx,
                                             GR_COORD by,
                                             int type);

Draws an arc with the specified dimensions at the specified position on
the specified drawable using the specified graphics context. The type
specifies the fill type. Possible values include GR_ARC and GR_PIE.

          id :  the ID of the drawable to draw the arc on
          gc :  the graphics context to use when drawing the arc
           x :  the X coordinate to draw the arc at relative to the
                drawable
           y :  the Y coordinate to draw the arc at relative to the
                drawable
          rx :  the radius of the arc on the X axis
          ry :  the radius of the arc on the Y axis
          ax :  the X coordinate of the start of the arc relative to the
                drawable
          ay :  the Y coordinate of the start of the arc relative to the
                drawable
          bx :  the X coordinate of the end of the arc relative to the
                drawable
          by :  the Y coordinate of the end of the arc relative to the
                drawable
          type :  the fill style to use when drawing the arc

-- 
------- Alex Holden -------
http://www.linuxhacker.org/
 http://www.robogeeks.org/

: Should I send you the patch again, Greg?

Yes.  Sorry, I seem to have forgotten about this.


:           ax :  the X coordinate of the start of the arc relative to the
:                 drawable
:           ay :  the Y coordinate of the start of the arc relative to the
:                 drawable
:           bx :  the X coordinate of the end of the arc relative to the
:                 drawable
:           by :  the Y coordinate of the end of the arc relative to the
:                 drawable

I included GrArc() for those tiny systems that don't have 
floating point support.  The ax,ay and bx,by values specify
any point on the line from the arc centerpoint through the
initial point and end point of the arc to be drawn, respectively.
This function is included because if an angle is specified, then
we've got to drag in floating point for the tan/atan function.

An easier function to understand is GrArcAngle, where the 
arc is specified in 1/10 degrees, rather than the strange start/end
point values in GrArc.  Check out src/engine/devarc.c for to see how
GrArcAngle ends up calling GrArc, which then draws the arc.

Regards,

Greg