makeLine w/ center coord rather than x1,y1,x2,y2?

[Barton, Robert]

Hi everyone,

I'm guessing this will be a quick "No", but I figured I'd try asking
anyways...

When writing a macro, is it possible to draw a line based upon the center
point of that line?  IOW, rather than using makeLine(156,197,356,197),
could I create a line by specifying the center point (256,197 in this case)
and then specifying how long the line should be?

Thanks.

[dscho]

Hi,

On Tue, 17 Jul 2007, Robert Barton wrote:

> When writing a macro, is it possible to draw a line based upon the
> center point of that line?  IOW, rather than using
> makeLine(156,197,356,197), could I create a line by specifying the
> center point (256,197 in this case) and then specifying how long the
> line should be?

First, you'd need the angle, too.  Second, it is easy to write a (macro)
function which does that:

-- snip --
function makeLine2(centerX, centerY, length, angle)
{
        angle = -angle * PI / 180;
        dX = cos(angle) * length / 2;
        dY = sin(angle) * length / 2;

        makeLine(centerX - dX, centerY - dY, centerX + dX, centerY + dY);
}
-- snap --

Ciao,
Dscho

[ctrueden]

Hi Robert,

The center point of the line together with the line length is
insufficient information to draw it -- you are missing the slope.
However, it should be quite to do some quick math (point slope
formula) on center point + slope + length to obtain the (x1,y1) and
(x2,y2) coordinates required to call drawLine.

-Curtis

On 7/17/07, Robert Barton <[hidden email]> wrote:

> Hi everyone,
>
> I'm guessing this will be a quick "No", but I figured I'd try asking
> anyways...
>
> When writing a macro, is it possible to draw a line based upon the center
> point of that line?  IOW, rather than using makeLine(156,197,356,197),
> could I create a line by specifying the center point (256,197 in this case)
> and then specifying how long the line should be?
>
> Thanks.
>

[lechristophe]

Hi Robert,

You would also have to specify an angle, because just the center point
and the length will not define a unique line. If you specify these four
parameters : the center, the length and an angle (relative to a
reference), you can easily use them to compute the four coordinates of
the end points.

A : the angle relative to the horizontal direction
x0, y0 : coordinates of the center
L : length of the segment

then the coordinates of the end points (x1,y1 and x2,y2) are

x1 = x0-0.5*L*cosA
y1 = y0-0.5*L*sinA

x2 = x0+0.5*L*cosA
y2 = y2+0.5*L*sinA

or something like that ;)

Cheers

Christophe


Christophe

Robert Barton a écrit :

> Hi everyone,
>
> I'm guessing this will be a quick "No", but I figured I'd try asking
> anyways...
>
> When writing a macro, is it possible to draw a line based upon the center
> point of that line?  IOW, rather than using makeLine(156,197,356,197),
> could I create a line by specifying the center point (256,197 in this case)
> and then specifying how long the line should be?
>
> Thanks.
>