Re: Drawing views into NSImage

FROM : Geert B. Clemmensen
DATE : Tue Apr 05 10:03:06 2005

Hello,

As usual, jcr's help turned out to be invaluable.

> I would expect that when you tried to draw more than one view on the
> same image, they all tried to draw in the lower-left corner?


Yes, although I could use NSAffineTransform to "move" 0,0, but never in
a consistent way.

> To find out where to put the origin, you can probably just send
> -convertPoint:toView: to each subview you want to draw,


Here the light bulb got turned on. Normally, a drawRect: method can
safely assume that focus has been locked, clipping is set up, and
lower-left is 0,0. When drawing into an NSImage, none of these
assumptions are applicable, the upside is that the drawRect: method
pretty much can draw wherever it wants. In the given case, the subviews
I wanted drawn into an NSImage are actually custom NSControls, each
with two NSTextFieldCell's and one NSButtonCell. I then wrote a
drawRectIntoImage:(NSPoint) newOrigin method which will make sure that
drawing happens at appropriate place inside the NSImage.

Now things work like a charm.

Regards,
Geert B. Clemmensen
www.frontbase.com


On 4. apr 2005, at 20.13, John C. Randolph wrote:

>
> On Apr 3, 2005, at 11:27 PM, Geert B. Clemmensen wrote:
>
> Hello,
>
> I have N views (or more specifically, N subviews of a content view
> that holds M subviews with M >= N). I want to draw these N views into
> an NSImage. I calculate the proper rect and initializes an NSImage
> instance accordingly, i.e. its size matches that of the calculated
> rect. I then do:
>
>     [myImage lockFocus];
>         // fill the image with clearColor
>         // draw the N views via drawRect: calls
>     [myImage unlockFocus];
>
> This kinda works, i.e. I get an NSImage that almost looks right, but I
> haven't been able to consistently have the N views draw so their
> relative position to each other is kept. I have tried enough variants
> of NSAffineTransform with -concat/-set (with and without
> save/restoreGraphicsState) to realize that this may not be the way to
> go. What is the recommended/preferred way to change the coordinate
> system before each call to drawRect:?
>
> I believe I have googled and otherwise searched the topic quite
> extensively, but haven't yet found a solution. Any pointers will be
> highly appreciated.
>
> What's tripping you up here is most likely the fact that when the
> drawing desination isn't an NSView, NSView's bounds and frame
> manipulation methods are no-ops.
>
> I would expect that when you tried to draw more than one view on the
> same image, they all tried to draw in the lower-left corner?
>
> If the  view in question is visible in a window on screen, you should
> be able to get what you want with NSBitmapImageRep's
> -initWithFocusedViewRect:, or NSView's -dataWithPDFInsideRect:
> methods.  If the view isn't in a window already, then  what you'll
> need to do is draw the views in their view hierarchy order, and
> manually set up the coordinate space (and clipping) before  drawing
> each one.  To find out where to put the origin, you can probably just
> send -convertPoint:toView: to each subview you want to draw, and
> discover any scaling using -convertSize:toView: using a size of {
> 1.0,  1.0 }.
>
> -jcr
>
>
> John C. Randolph <<email_removed>> (408) 974-8819
> Sr. Cocoa Software Engineer,
> Apple Worldwide Developer Relations
> http://developer.apple.com/cocoa/index.html
>
>
>
>