Re: [css3-transform] definition of skewing

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