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Re: [css3-transform] definition of skewing

From: Chris Marrin <cmarrin@apple.com>
Date: Mon, 17 Jan 2011 14:48:36 -0800
Cc: Simon Fraser <smfr@me.com>, "www-style@w3.org" <www-style@w3.org>
Message-id: <F1DCC71E-9025-4A42-9ED2-A8973DA1FDF6@apple.com>
To: Rik Cabanier <cabanier@adobe.com>

On Jan 13, 2011, at 12:22 PM, Rik Cabanier wrote:

> Yes,
> 
>  
> 
> Rotate is always around the transformation point.
> 
>  
> 
> Rotate(a) is defined through the matrix:
> 
> | cos(a) -sin(a) 0 |
> 
> | sin(a) cos(a)  0 |
> 
> | 0        0          1 |
> 
>  
> 
> Rotate(a, b) would be defined as:
> 
> | cos(a) -sin(b) 0 |
> 
> | sin(a) cos(b)  0 |
> 
> | 0        0          1 |

I don't see a reason to have such a function. If an author wants to do such transformations, he can use matrix().

> 
>  
> 
> This type of animation is often used in Flash to give the appearance of an object that turns into view.
> 
>  
> 
> Also, I believe that there should be a skew(x, y).
> 
> The way the formulas are currently defined, there is no easy way to correctly do a shear in 2 dimensions since the second shear will impact the first one.
> 
> There should either be a skew(x, y) or the recomposition logic should be rewritten.

Again, that's what matrix() is for. A skew(x,y) primitive would always have the issue of ordering between x and y. I think the current primitives are plenty for allowing authors to construct matrices.

-----
~Chris
cmarrin@apple.com
Received on Monday, 17 January 2011 22:49:13 GMT

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