W3C home > Mailing lists > Public > whatwg@whatwg.org > July 2010

[whatwg] Canvas transform() and matrix element notation

From: Yp C <tccyp86@hotmail.com>
Date: Tue, 20 Jul 2010 05:44:37 +0800
Message-ID: <BAY150-w3ADD5CF9EC475912ECF1BBCBF0@phx.gbl>



> Date: Mon, 19 Jul 2010 14:33:01 -0700
> From: david at davidflanagan.com
> To: bzbarsky at MIT.EDU
> CC: whatwg at lists.whatwg.org
> Subject: Re: [whatwg] Canvas transform() and matrix element notation
> 
> Boris Zbarsky wrote:
> > On 7/19/10 4:13 PM, David Flanagan wrote:
> >> The spec describes the transform() method as follows:
> >>
> >>> The transform(m11, m12, m21, m22, dx, dy) method must multiply the
> >>> current transformation matrix with the matrix described by:
> >>>
> >>> m11 m21 dx
> >>> m12 m22 dy
> >>> 0 0 1
> >>
> >> The first number in these argument names is the column number and the
> >> second is the row number.
> > 
> > I agree that this is somewhat weird at first glance, but it seems to be 
> > not uncommon for graphics libraries.  For example, for cairo the call
> > 
> >   cairo_matrix_init(m, a, b, c, d, e, f);
> > 
> > creates a matrix which represents the affine transformation [1]:
> > 
> >  x_new = a*x + c*y + e;
> >  y_new = b*x + d*y + f;
> > 
> 
> Thanks for checking this; it is nice to know that there is precedent for 
> the argument order. Changing the argument names to remove the numbers 
> from them would make the spec less confusing.  Or at least changing the 
> argument names so that they use (standard?) row,column indexing instead 
> of column,row indexing.
> 
>      David

But I think the number can indicate the position of the value in the matrix,if change them into "a,b,c..." like cairo, I think it will still confuse the beginner. 		 	   		  
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