I'd like to know how WebKitCSSMatrix actually works

Question

Apple's official documentation says:

WebKitCSSMatrix objects represent a 4x4 homogeneous matrix for 3D transforms or a vector for 2D transforms. You can use these objects to manipulate matrices in JavaScript. For example, you can multiply, translate, and scale matrices.

I'm a glorified designer, not an engineer, so I'm assuming that's the reason why I can't make any sense of that description. Please, can somebody point me in the right direction to understand how this matrix and/or vectors work?

Answer 1

Whew, this is the most difficult question I've attempted to answer. The short answer is that, as web designers, we don't have the vocabulary to express 3d transformations. In order to explain it to you in a comprehensible way I'd have to use math concepts which I don't understand myself.

If you'd like to investigate further you can take a look at: http://www.eleqtriq.com/2010/05/css-3d-matrix-transformations/

But, I can explain it visually. http://duopixel.com/stack/webkitmatrix/ (you'll have to view this under Safari 5 w/Snow Leopard, or an iPad, or course).

What you're seeing is just an interface to the 16 values webkitCSSMatrix, the sliders that seem to do nothing are related to the z axis, which I suspect would be visible if we had more objects in the 3d canvas.

Edit: after studying the link I placed before, I noticed the original author has done the same example before, doh! http://www.eleqtriq.com/wp-content/static/demos/2010/css3d/matrix3dexplorer.html

Answer 2

Even though it's for ActionScript, check out Understanding the Transformation Matrix in Flash 8. It's got pretty pictures, too :)

Before getting into how transformation matrices (matrices is plural of matrix) work, it is important to understand what a matrix is. A matrix is a rectangular array (or table) of numbers consisting of any number of rows and columns. A matrix consisting of m rows and n columns is known as an m x n matrix. This represents the matrix's dimensions. You'll commonly seen matrices with numbers in rows and columns surrounded by two large bracket symbols.

...

Affine transformations are transformations that preserve collinearity and relative distancing in a transformed coordinate space. This means points on a line will remain in a line after an affine transformation is applied to the coordinate space in which that line exists. It also means parallel lines remain parallel and that relative spacing or distancing, though it may scale, will always maintain at a consistent ratio. Affine transformations allow for repositioning, scaling, skewing and rotation. Things they cannot do include tapering or distorting with perspective. If you're ever worked with transforming symbols in Flash, you probably recognize these qualities.

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