Re: Mouse position from NSEvent starts at (0, 1) ?
Re: Mouse position from NSEvent starts at (0, 1) ?
- Subject: Re: Mouse position from NSEvent starts at (0, 1) ?
- From: "Mathieu Coursolle" <email@hidden>
- Date: Tue, 15 May 2007 15:41:53 -0400
- Organization: Rogue Research
However, I experience the offset for every mouse positions.
I am always drawing the cross one pixel too far in the Y direction.
Thanks.
>I'd say it is a rounding issue...
>the mouse might be at 0.7!?
>
>On May 15, 2007, at 9:30 PM, Mathieu Coursolle wrote:
>
>> Hi cocoa developers,
>>
>> I created a subclass of NSView to draw a 1 pixel thick cross at the
>> mouse cursor position. However, the cross is offset by one pixel in
>> the
>> Y direction.
>>
>> In the mouseDragged: method, I use the following code to get the view
>> coordinates:
>>
>> NSPoint pt = [self convertPoint:[theEvent locationInWindow]
>> fromView:nil];
>>
>> Then in drawRect: I draw a cross at that position like so:
>>
>> - (void)drawRect:(NSRect)rect
>> {
>> // Gray background.
>> [[NSColor colorWithCalibratedRed:0.2 green:0.2 blue:0.2 alpha:
>> 0.2] set];
>> [NSBezierPath fillRect:[self bounds]];
>>
>> // Red cross.
>> [[NSColor colorWithCalibratedRed:1.0 green:0.0 blue:0.0 alpha:
>> 1.0] set];
>> [NSBezierPath fillRect:NSMakeRect(x, y-100, 1, 200)];
>> [NSBezierPath fillRect:NSMakeRect(x-100, y, 200, 1)];
>> }
>>
>> It seems like the cross is drawn at the position I ask for, but the
>> mouse cursor position I get is offset.
>>
>> When I click the bottom left pixel of the view, I get (0, 1)
>> coordinates
>> (pt in code above). Shouldn't it be (0, 0)? I have to draw at (0,
>> 0) to
>> draw that pixel.
>>
>> I came across an old post describing exactly the same problem:
>> <http://www.omnigroup.com/mailman/archive/macosx-dev/2000-March/
>> 013028.html>
>>
>> I can solve the problem by doing something like:
>>
>> pt.y = pt.y - 1;
>>
>> but I would like to have an explanation for this. ;)
>>
>> Anyone can explain this behaviour?
>>
>> Thank you.
>>
>> Mathieu
>>
>>
>>
>>
>>
>>
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