> I've been so used to only being able to drag directly on the
> control points from all my other applications!

It's not too uncommon for 2D Bezier illustration programs to support a version of this, like in Adobe Illustrator you can click and drag directly on a curve when control points are visible to move it.

But actually the behavior of this "direct curve drag" in these Bezier apps kind of highlights the segmented nature of the pure Bezier approach - over there when you click and drag on a curve, the ends of the segment stay anchored and only the interior 2 points are adjusted. This tends to cause curly-cues and it really spazzes out if you try to drag a point close to the end of a Bezier segment, a tiny motion there causes kind of a huge reaction in the curve. It's not really a full "roughing out" tool over there since only the one segment is effected by the drag.

The NURBS-based direct curve dragging in MoI gives a lot more smooth editing results at any point along a curve.


I'm not really sure why 2D illustration apps have never upgraded to use NURBS-based technology instead of only Bezier-based. I guess Adobe Illustrator never did it because Illustrator is kind of part of a larger Adobe ecosystem and it has been meant to be on par with other parts such as the Postscript language. So they probably don't want to upgrade just one thing, they would want to upgrade a whole bunch of things, making it easier to decide not to upgrade at all. Then other 2D illustration stuff follows their lead...

- Michael

Hi Jesse - there are actually 2 different ways of adding control points.

Kind of the common way in MoI is to add a new point on the control polygon hull in between 2 existing points. This way will change the shape of the curve though, it will generally be the equivalent as if you had drawn the original curve including those new points you added. That's why it is kind of the normal way because it works equivalent to drawing a curve by control points.

But there is a second way of adding a control point where you can add it directly to a curve without disturbing the shape of the curve (same as InsertKnot in Rhino). This will happen if you click directly on the curve when inside of AddPt instead of on the control point hull. But by default the control point hull (the dashed lines between control points) has priority, so if you have control points showing it can be difficult to grab a point on the curve, but if you turn control points off then you will be able to grab the curve directly for this second mode.

If you add points using the second method, the shape of the curve will remain exactly the same and instead the control points themselves will slightly shift. The first way it is the reverse - the control points stay anchored down and the curve will shift shape instead.

- Michael

Hi Michael,


Thanks for the explanation.. I see how it works differently.
And by adding a "loose" point from the curve menu as a marker,
you can see where the joint is without having to turn control points on.

Jesse

As michael pointed out, i added the point directly onto the curve. and here is the example of 3 points added very close to the joined end points, and then deleting the end point itself. you can see the change does not pass beyond the 3rd extra point...

jonah

Michael wrote:
"I'm not really sure why 2D illustration apps have never upgraded to use NURBS-based technology instead of only Bezier-based. I guess Adobe Illustrator never did it because Illustrator is kind of part of a larger Adobe ecosystem and it has been meant to be on par with other parts such as the Postscript language. So they probably don't want to upgrade just one thing, they would want to upgrade a whole bunch of things, making it easier to decide not to upgrade at all. Then other 2D illustration stuff follows their lead..."

Just the other day I was wishing I could do simple surface coloring with MOI since creating shapes with it is so easy - I guess I'll have to wait for the AI export features.

I wanted to load a UV map image of a spaceship wing and start drawing hull plating patterns over the UV map - MOI is great for drawing curves, I wish Fireworks, CorelDraw and Illustrator also used the same kind of editing features as well!

If I could have used MOI to draw my hull patterns and then select a few of the closed shapes and colored them to get some base colors going that would have been great.

I of course can color in my shapes elsewhere but it would have been cool!

-Will

Theres some great info here, thanks Jonah with that initial suggestion and with Michaels clarification it sounds like a neat solution! I guess you wouldn't want to script this action because you want to choose where the additional control points go yourself, but it's no hassle at all.
Lovely jubbly

Hi Michael,

I tried the other method a few times and can see the benefit of removing a joint with control points turned off and using 3 tightly grouped points on each side of the seam point, before removing it, but in practicality, I realized that with the most of the designs I do, I will place a corner point where I want to define the start of a new surface but with that, I either draw straight continuous lines or graceful flowing curves without tightly angled transitions as in Jonah's example. If I remove points to adjust an irregular transition in a curve or remove a seam point, I'm usually editing the shape from a broader perspective anyway, so it seems more efficient for me to keep the control points on, to take out a seam. It's helpful to know how to do it the other way, too. So thanks, now I know there's a method to my madness. :-)

Regards,
Jesse

If you want a fun and easy to use vector illustrator, try Inkscape. It's scriptable with Python, and has all sorts of ways to easily tweak curves. You can just click and hold on any part of a curve, and drag it where you need. No need to use the handles on the control points.

I highly reccomend it, and I also think Moi should support SVG import.

Michael:

I just wanted to say, clicking and dragging anywhere on a curve to modify it has been in Inkscape for a few releases now... ;)

Maybe you can steal a few of their other ideas as well.... <:)

Pattern along path:
Mmm, imagine this applied to arrays in Moi.
http://www.inkscape.org/screenshots/gallery/inkscape-0.45-patternalongpath.png

Thicken and thin closed curves, and Guide Paths
http://www.inkscape.org/screenshots/gallery/inkscape-0.46-engraving2.png
http://www.inkscape.org/screenshots/gallery/inkscape-0.46-engraving1.png

Drag the Curve to edit it:
http://www.inkscape.org/screenshots/gallery/inkscape-0.43-nodeedit.png

Node Sculpting: ( Think Uber Curve Drag )
http://www.inkscape.org/screenshots/gallery/inkscape-0.44-nodesculpting.png

Hi Crusoe - there are tons of cool things in Inkscape, no doubt. In the future I would like to incorporate some of this type of 2D illustration flavored stuff.

However, the "drag directly on curve" inside of Inkscape has the same problem as Adobe Illustrator - again, it kind of goes hand-in-hand with the segmented nature of Bezier editing.

Here are some screenshots from Inkscape to illustrate:



Here you can see that I grabbed a point on the curve not far from the end node, and dragged upwards not too far. This produced a big shift in the curve, the tangent has swung around about 90 degrees from this small distance, and kind of a bulge developed on the other side of the node.

This is because during the "point on curve" dragging, the end nodes are fixed in position. The bezier segments are the portions in between each of those on-curve nodes.


If you compare this to MoI's NURBS based dragging, you won't see any "fixed in place" portions of the curve during the drag like this. This is because NURBS allows for a single segment with more than 4 points in it. Beziers are limited to segments that are made up of only 4 points, and a longer curve is a string of these 4-point segments sort of glued end to end.

That's just one area where the NURBS approach makes for smoother processing since you can have longer segments. The actual geometric smoothness of the curve is better with NURBS, Beziers have breaks in the curvature between each of the little 4 point segments unless every single node is set to the symmetrical type...

The editing in Inkscape is a lot friendly overall than Adobe Illustrator though - I've always had difficulty selecting stuff in Illustrator, they made it pretty hard to target the little points in there, the interaction feels pretty nice inside of Inkscape in comparison.

- Michael

Holy Moo! This is cool!