> Date: Thu, 24 Jan 2013 12:01:28 +1100 > From: Graham Cox <graham....@bigpond.com> > To: "cocoa-dev@lists.apple.com Dev" <cocoa-dev@lists.apple.com> > Subject: Re: Coordinate conversions in CALayer
> Boiling down my problem to its bare essentials, why are these two bits of > code not equivalent? > > > > CGContextTranslateCTM( ctx, pos.x, pos.y ); > CGContextConcatCTM( ctx, layer.transform ); > CGContextTranslateCTM(ctx, -(br.origin.x + anch.x * br.size.width), > -(br.origin.y + anch.y * br.size.height)); > > The above works correctly, but below, which I thought should do the same, > does not, if the layer.transform property is not the identity matrix: > > > > CGAffineTransform tfm = CGAffineTransformMakeTranslation( pos.x, pos.y > ); > tfm = CGAffineTransformConcat( tfm, layer.transform ); > tfm = CGAffineTransformTranslate( tfm, -(br.origin.x + anch.x * > br.size.width), -(br.origin.y + anch.y * br.size.height)); > > CGContextConcatCTM( ctx, tfm ); They are not equivalent because the first one starts with CGContextTranslateCTM but the second one starts with CGAffineTransformMakeTranslation. In other words, the first one begins by translating the current transform. The second one begins with a plain vanilla translation. The affine transform equivalent of CGContextTranslateCTM is CGAffineTransformTranslate. You might want to say this: CGAffineTransform tfm = CGAffineTransformTranslate( layer.transform, pos.x, pos.y ); m. -- matt neuburg, phd = m...@tidbits.com, http://www.apeth.net/matt/ pantes anthropoi tou eidenai oregontai phusei Programming iOS 5! http://shop.oreilly.com/product/0636920023562.do RubyFrontier! http://www.apeth.com/RubyFrontierDocs/default.html TidBITS, Mac news and reviews since 1990, http://www.tidbits.com _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
