Re: Select a NSBezierPath
Re: Select a NSBezierPath
- Subject: Re: Select a NSBezierPath
- From: Lorenzo <email@hidden>
- Date: Tue, 21 Sep 2004 21:49:35 +0200
Yes, thanks,
currently I have found that the best method is to get a flattening path
[NSBezierPath setDefaultFlatness:0.1];
NSBezierPath *flatPath = [aPB bezierPathByFlatteningPath];
Then I iterate for each element of the flatPath and intersect the "i"
element rect with the clickPoint rect until the intersected rect has widht
or height > 0. It works like a charm, even with several paths on the screen.
And without any extra drawing nor offScreens.
float clickRectSize = 4.0;
NSRect clickRect = NSMakeRect(
clickPoint.x - clickRectSize / 2,
clickPoint.y - clickRectSize / 2,
clickRectSize , clickRectSize);
Remember to set back the defaultFlatness to its previous default value.
Also, it would be so nice to have an API which returns the lower "y" value,
given an "x" value of the path. Or returning an array containing all the "y"
values found for that "x" coordinate. The first index of the pointArray
should be the lower "y" value.
This should help a lot when using the path for animating objects.
:-)
Best Regards
--
Lorenzo
email: email@hidden
> From: Graham Cox <email@hidden>
> Date: Tue, 21 Sep 2004 18:11:34 +1000
> To: "John C. Randolph" <email@hidden>
> Cc: Lorenzo <email@hidden>, Cocoa Developers List
> <email@hidden>
> Subject: Re: Select a NSBezierPath
>
> It sounds simpler, but it's much slower.
>
> When you draw a Bezier curve, you have to first compute the curve, then
> rasterize it into a buffer, then hit test that. The mathematical
> approach involves only the first of these steps, and it can bail early
> if a hit is found. The drawing step is the killer, dwarfing the time
> the rest takes. I'm not sure if there are ways to get around this with
> NSBezierPath - I guess turning off antialiasing and setting the
> flatness to a coarser value would help.
>
> I'm not dismissing the approach, but I found that for 2D drawing and
> hit testing, the calculation approach was much faster. If the graphics
> don't change much, I guess the drawing step can be avoided most of the
> time, so it may become a better technique for some situations. In a
> drawing editor, by definition the graphics tend to change quite often.
>
> --Graham
>
>
> On 21 Sep 2004, at 9:50 am, John C. Randolph wrote:
>
>> There is a much simpler way to do this, which Michael Johnson at Pixar
>> explained to me a couple of years ago. The approach he described is
>> to use an off-screen drawing destination, and draw each object that
>> you want to check for hits in a distinct color. Then, given a
>> location, look at the color at that point, and use the color as an
>> index to the object that you've hit. This technique has been used
>> for many years in the 3D animation industry.
>>
>> -jcr
>>
>>
>>
>> On Sep 20, 2004, at 3:54 PM, Graham Cox wrote:
>>
>>> Detecting hits on the path itself is a moderately hard problem, but
>>> certainly not impossible. If you're doing a lot of this type of thing
>>> with bezier curves NSBezierPath might be too opaque. I'm working on a
>>> vector drawing program and found exactly this, so in the end I
>>> decided to create my own bezier class that handles all the stuff that
>>> NSBezierPath doesn't. A bit of hunting around on the net soon turned
>>> up literally thousands of sites explaining the maths involved, which
>>> is actually very straightforward. By combining my own bezier class
>>> with the drawing features provided by NSBezierPath, I can do all this
>>> and much more. Also search for "graphics gems".
>>>
>>> One thing to watch out for though is that the very popular
>>> deCasteljau's recursive algorithm which is frequently put forward as
>>> a "good" way to build beziers is in practice slow - there are much
>>> faster practical methods.
>>>
>>> Essentially detecting a hit on the path involves walking the list of
>>> curve points, treating pairs of successive points as defining a
>>> straight line, and calculating the distance from this line of the hit
>>> point. If this distance drops below some defined minimum, it counts
>>> as a hit (note that you have to allow some tolerance, since the path
>>> is infinitely thin, hitting it exactly is nigh on impossible). My
>>> class does some optimisations to cut down on the sheer number of
>>> calculations needed, so in practice the hit testing and other stuff
>>> is fast. This list of points can be quite coarse, since you are not
>>> using it to draw a curve - you can use NSBezierPath for that - which
>>> also helps make it fast.
>>>
>>> If you're interested in this approach contact me off list and I'll
>>> happily share the code with you, though at the moment it's rather
>>> specific to my application.
>>>
>>> --Graham
>>>
>>>
>>>
>>>
>>>
>>> On 21 Sep 2004, at 12:28 am, Lorenzo wrote:
>>>> Hi,
>>>> I have 2 NSBezierPath with lines and curves only (not closed) and I
>>>> try to
>>>> select one of them at mouseDown
>>>>
>>>> if([bp1 containsPoint:thePoint]){
>>>> selected = 1;
>>>> }
>>>> else if([bp2 containsPoint:thePoint]){
>>>> selected = 2;
>>>> }
>>>>
>>>> but even if I don't click on the lines, the API "containsPoint"
>>>> returns YES.
>>>> And this is wrong.
>>>> This happens because I click in a zone which, I presume, if the path
>>>> was
>>>> closed/filled, should appear coloured.
>>>> But I click on an empty zone, and the path is not closed, so, since
>>>> I don't
>>>> click on the lines of the path I should not select it.
>>>> This sometimes causes I select the path1 instead of the path2, which
>>>> really
>>>> is the path I clicked on. Thus this is wrong.
>>>>
>>>> - Q1: How to fix this?
>>>> - Q2: How to get the coordinates x and y of "any" point of the path?
>>>> As I wrote here earlier, I am trying to build a Sound-Volume/Time
>>>> control such a way I can set different volume levels in different
>>>> time-points of the song. It's something like the Sound-Volume control
>>>> in iMovie.
>>>> - Q3: Am I on the right way?
>>>> - Q4: If not, how to create such a control?
>>>>
>>>>
>>>> Best Regards
>>>> -- Lorenzo
>>>> email: email@hidden
>>>>
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