[Drawkit] DKTextShape rotation

[Allan]

Hi Graham,

The setOffset method did exactly what I needed and made everything  
easy. Worked like a charm.

I haven't used the debugging method you wrote about yet, but it looks  
useful.

Thanks.

-Allan


On Feb 12, 2009, at 3:39 PM, Graham Cox wrote:

>
> On 13 Feb 2009, at 4:57 am, Allan wrote:
>
>> Hi Graham,
>>
>> I'm still working on implementing the TEXT entity import from the  
>> DXF format into DK. It has been a tougher nut to crack than I  
>> expected. Here's my current issue that I wonder if you could  
>> comment on.
>>
>> In AutoCAD (and the resulting DXF) when TEXT is rotated it is not  
>> necessarily rotated around the center point. AutoCAD uses the  
>> concept of an "insertion point" which is the origin or base point  
>> of the TEXT object. If you rotate text, it gets rotated with  
>> respect to this insertion point.
>>
>> I think that in DK all DrawableObject rotations happen around the  
>> object center/middle point. Is that correct? If so, for me to place  
>> a rotated text object correctly would require me to do some math  
>> where I would use the AutoCAD insertion point and the rotation  
>> angle with some sines and cosines to figure out the correct DK  
>> origin and then apply the rotation.
>>
>> Is that right? All DK objects are rotated around the center/middle?  
>> Or is there a clever DK method to modify the rotation point for an  
>> object that I could use to more directly get the TEXT object  
>> located correctly?
>>
>> Thanks for any help you can send.
>
>
> Hi Allan,
>
> All shapes (including text shapes) allow you to set the 'point of  
> rotation' anywhere within the bounds of the shape. By default it's  
> the middle, but you can move it anywhere.
>
> In the UI an ordinary shape uses a centre target cross to show where  
> this is, and you can click and drag this to set the centre. In a  
> text shape, this knob is turned off so that it doesn't get in the  
> way of reading the text, and as a result it's not draggable. That  
> doesn't prevent you from setting it programatically, and/or you can  
> turn the visibility of that knob back on if you want to make it  
> interactive.
>
> To set it programmatically, use -setOffset:
>
> This accepts a NSSize argument that is the relative amount of  
> displacement from the centre to the unrotated bounds edge. That  
> sounds complicated but it's easy to understand with an example. An  
> offset of {0,0} is the centre. An offset of {-0.5, -0.5} is the top,  
> left (or bottom, left in unflipped coordinates) of the object, and  
> offset = {0.5, 0.5} is the bottom right. Specifying the offset this  
> way makes it always proportional to the current size of the object  
> so rotation does the expected thing.
>
> If you want to make the knob for this visible in a text object, in  
> the current version you'll need to change the mask returned by  
> +knobMask, which is hardcoding the clearing of the  
> kDKDrawableShapeOriginTarget flag. I need to change that to use the  
> more recent approach of using +setKnobMask so you can simply set it  
> as you wish.
>
> When you're placing text objects programmatically, if you set the  
> offset prior to setting the location and angle of the object, you  
> should be able to simply place the object without having to do any  
> maths - the offset also sets the position that the object considers  
> its location to be measured from, so for example if you set the  
> offset to the bottom, left of the text, and that's where the DXF  
> file considers its text labels to be located, then you can just call  
> -setLocation: with the same value (and angle). When the offset is  
> changed interactively the location is compensated so the object  
> doesn't move within the drawing, but the actual value of -location  
> is changing. Hope that makes sense. Rather than 'point of rotation'  
> think of the offset as setting the object's datum. The location and  
> rotation are relative to this datum point.
>
> Also, while we're on this topic, here's a handy debugging or  
> introspection technique that can sometimes be useful to "see" what's  
> happening to certain values as you interact with objects, such as  
> dragging them or their control knobs. Create a text adornment style  
> and set its identifier to '$<keypath>', where <keypath> is some  
> property of interest, let's say 'offset'. Then the object that has  
> this style attached will display the value of that property right  
> there in the object, and it will be updated live whenever it  
> changes. The '$' prefix is there to tell the adornment to look up  
> the value as a property not as a metadata key. After that it's just  
> using KVC.
>
> --Graham
>
>
>
>
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