[Drawkit] Scaling issues

[Brad Larson]

This does the trick for the really high zoom factors that we'd need in  
our particular case (~250 for units of microns), so I re-enabled the  
proper units on drawing loading.  That's working perfectly for us, now.

For zooming out, drawing programs like Inkscape and OmniGraffle change  
the grid spacing dynamically as you zoom out while maintaining a 1  
point line width so that there's still a grid to work off of but the  
view is filled with lines.  That's a trickier operation to pull off,  
but it might be something to think about for the future.

On May 23, 2008, at 8:35 PM, Graham Cox wrote:

>
> On 24 May 2008, at 10:47 am, Graham Cox wrote:
>
>> nce the linewidth can be set independently of actually constructing  
>> the grid cache it would be easy to set this on the fly taking into  
>> account the zoom without invalidating the cache itself. I'll have a  
>> look at that this morning.
>
>
> I modified the grid to use the following code in its - 
> drawRect:inView: method. It prevents the drawn line width from  
> exceeding 1 pixel but does so in a way that comes into force  
> smoothly as you zoom. Other things I tried caused abrupt changes in  
> the appearance of the grid which I didn't like. I also don't bother  
> drawing the finest part of the grid when zoomed out more than a  
> factor of 2 - at that scale you can't see this part of the grid so  
> no point drawing it.
>
> Give this a try and see how it works for your situation. I have  
> tried it with a zoom range from 0.025 to 250x (10000:1) and I find  
> it acceptable (at very high zooms the span and divs lines become  
> hard to tell apart but I don't think that's a big problem). I do  
> also notice a very slight rounding error misalignment at maximum  
> zoom (the ruler mark and the span line are misaligned by a couple of  
> pixels). I think this is just hitting the limits of precision of a  
> floating point value, so there may be nothing that can be done about  
> it.
>
> You need to #import DKDrawKitMacros.h to get the LIMIT macro.
>
> 		else
> 		{
> 			// draw directly from the cache. Apply the linewidth accounting  
> for the view's scale factor
> 			
> 			float zoom = [aView scale];
> 			float dlw, slw, mlw;
> 			
> 			dlw = LIMIT( m_divisionLineWidth / zoom, 0.05, 1.0 );
> 			slw = MIN( m_spanLineWidth / zoom, 1.0 );
> 			mlw = MIN( m_majorLineWidth / zoom, 1.0 );
> 			
> 			// make sure the actual drawn line width can't exceed 1 pixel
> 				
> 			if ( zoom * slw > 1.0 )
> 				slw = 0;
>
> 			if ( zoom * mlw > 1.0 )
> 				mlw = 0;
> 			
> 			[m_spanCache setLineWidth:slw];
> 			[m_majorsCache setLineWidth:mlw];
> 			
> 			// don't draw the smallest divisions at all if we are zoomed out  
> more than 0.5 - you can't
> 			// see them anyway so no point spending time drawing them
> 			
> 			if ( zoom >= 0.5 )
> 			{
> 				if ( zoom * dlw > 1.0 )
> 					dlw = 0;
> 				
> 				[m_divsCache setLineWidth:dlw];
> 				[m_divisionColour setStroke];
> 				[m_divsCache stroke];
> 			}
> 			[m_spanColour setStroke];
> 			[m_spanCache stroke];
> 			[m_majorColour setStroke];
> 			[m_majorsCache stroke];
> 		}
>
>
> cheers, Graham
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______________________
Brad Larson
SonoPlot, Inc.
3030 Laura Lane, Suite 120
Middleton, WI 53562