Hi there,

I'm trying to make inkscape a simple level editor for my team-mates but I'm kinda stuck on the transform attribute.
Basically we only use circles to position items, and I want to use the sodipodi:- rx ry cx cy properties. As I move them around they do not change, only the Matrix does ( I guess thats kinda logical).
But I need to get the position from cx cy and the radius from rx and ry. I have no idea how to apply the matrix to it.
Yes I did read the official site on matrices.

I know that for transformtion it's


scaling is



But these are 2 separate matrices.
And the "matrix" attribute is a combination of the translation, scaling and rotation right?

I'm really confused at how to find the individual scaling and translation in combination with the sodipodi attributes.

Have a look at this answer: http://stackoverflow.com/questions/4361 ... ion-matrix

Not all values of a,b,c,d,tx,ty will yield a valid rotation sequence. I assume the above values are part of a 3x3 homogeneous rotation matrix in 2D

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    | a  b  tx |
A = | c  d  ty |
    | 0  0  1  |

which transforms the coordinates [x,y,1] into:

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[x',y',1] = A * [x,y,1]

Thus set the traslation into [dx,dy]=[tx,ty], the scale is sx=sqrt(a^2+b^2) and sy=sqrt(c^2+d^2). Finaly the rotation angle is t=atan(c/d) or t=atan(-b/a) as also they should be the same.

Otherwise you don't have a valid rotation matrix.

The above transformation is expanded to:

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x' = tx + sx*(COS(t)*x-SIN(t)*y)
y' = ty + sy*(SIN(t)*x+COS(t)*y)

Nothing like going through something like this by hand to get things sorted in your head.

Oh, In case you missed it the spec is fairly good at describing how the matrixes work: http://www.w3.org/TR/SVG/coords.html