Re: NS <-> CG Rect Conversion and screen coordinates
Re: NS <-> CG Rect Conversion and screen coordinates
- Subject: Re: NS <-> CG Rect Conversion and screen coordinates
- From: Peter Ammon <email@hidden>
- Date: Wed, 1 Apr 2009 12:25:19 -0700
On Mar 31, 2009, at 9:34 PM, Trygve Inda wrote:
Using these two calls:
NSRect nsRect = [screen frame];
CGRect cgRect = CGDisplayBounds (displayID);
I get for my two screens:
NS x=0 y=0 w=2560 h=1600 // screen A
CG x=0 y=0 w=2560 h=1600
NS x=-1920 y=184 w=1920 h=1200 // screen B
CG x=-1920 y=216 w=1920 h=1200
It seems CG origin is Top, Left with y growing down, while NS is
origin
Bottom, Left, y growing up. So I convert CG to NS with:
// Convert CG coordinates from (TL, y down) to (BL, y up)
CGRect mainScreenRect = CGDisplayBounds (CGMainDisplayID ());
cgRect.origin.y = (cgRect.origin.y + cgRect.size.height -
mainScreenRect.size.height) * -1;
(216 + 1200 - 1600) * -1 = 184
Is there a system function that does this? NSRectFromCGRect does not
do the
coordinate conversion.
No, there is no function to do this conversion.
Note that your conversion has a subtle bug that will fail for multiple
displays. The CG coordinate system has its origin at the top of the
zero screen, not the main screen (which changes with the user focus).
The zero screen is the screen at index zero in the +screens array.
So if you define a function like this:
CGFloat zeroScreenHeight(void) {
CGFloat result = 0;
NSArray *screens = [NSScreen screens];
if ([screens count] > 0) result = NSHeight([[screens objectAtIndex:
0] frame]);
return result;
}
then you can do screen-coordinate conversions like this:
NSMakePoint(cgPoint.x, zeroScreenHeight() - cgPoint.y);
NSMakeRect(cgRect.origin.x, zeroScreenHeight() - cgRect.origin.y -
cgRect.size.height, cgRect.size.width, cgRect.size.height);
-Peter
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