# Re: Clarification of Parameters to Relative Cubic Bezier Spline / Bug

From: Andy Bailey <ambailey@usb.edu.co>
Date: Wed, 21 May 2003 11:39:45 -0500
Message-ID: <3ECBABD1.5000908@usb.edu.co>
To: Thomas E Deweese <thomas.deweese@kodak.com>

```

I have now seen it in the spec (after reading the information that comes
before the section about the splines).

I would just like to add that my reason behind what I wanted is that if
it were as I said I think there would be less dependent variables.
M sx sy c dx dy dx' dy' x' y' (if the dx' dy' is relative to the x', y')
then x' and y' could change without having to recalculate the dx' dy'.
The curve is essentially the same. Thats my programmers way of thinking
about the world, its easier to visualize when writing an svg file by
hand. Sure if you have a tool to do the calculation theres no problem.

I dont see that there are really 2 current points, to change it to what
the specification says c x1 y1 x2 y2 x y is easy: x2=x'+dx'
y2=y'+dy'
its just Id rather have the computer do the work for me.

I suppose since the specification is released that thats the way it has
to stay, even though its a minor point I think its a shame.

Thanks
Andy Bailey

Thomas E Deweese wrote:

>>>>>>"AB" == Andy Bailey <ambailey@usb.edu.co> writes:
>>>>>>
>>>>>>
>
>AB> In the specification of Relative Cubic Bezier Spline (svg 1.1) c
>AB> (x1 y1 x2 y2 x y)+ it does not what the parameters are relative to
>AB> ...
>
>    Trust me it does say a bit before where it would be useful to say
>it.  Finding the exact quote is left as an excercise for the reader.
>
>AB> I assumed that the x1 and y1 were relative to the current point
>AB> that x2 and y2 were relative to the final point of the curve (x,
>AB> y) and that x y were relative to the current point.
>
>AB> This seems to me to be logical
>
>    This is 'one' logical view I originally considered each to be
>relative to the precursor, neither is correct.
>
>AB> However I am using cocoon with batik to do the rendering and I
>AB> discovered that the x2 y2 is relative to the current point, this
>AB> doesnt seem to be logical.
>
>    I think this is done so that there is only one current point.
>
>AB> If one drew the diagram you would draw it as in the diagram
>AB> cubic01.png in the same page of the svg 1.1 specifications. (that
>AB> I am attaching)
>
>AB> Is this a bug in batik or is this the intended form of svg, in
>AB> either case I think the parameters need to be clarified.
>
>    It is the intended form of SVG.  I agree that a clarification of
>the specification text would be useful (the spec is clear).
>
>AB> To everyone involved in svg - thank you for all your hard work.
>
>
>
>
```
Received on Wednesday, 21 May 2003 12:51:50 UTC

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