rotate - method of the CanvasCtx object

The transformation allows to map the positions from one co-ordinate system to another. It can be used for drawing a shape into a magnified/reduced, rotated, shifted, mirrored 2D space. It is easier to transform the 2D space co-ordinates than recalculating the co-ordinates of all objects. All position stransformations are defined by 6 variables a, b, c, d, e, f (out of 9) of the 2D space transformation matrix. The default value of non-transformed 2D space is 1, 0, 0, 1, 0, 0 (so-called unit matrix). The transformation matrix is a part of the drawing area. The save and restore methods can save this matrix.

The transformation methods transform, translate, scale or rotate modify some (or all) values of the transformation matrix. Each method saves the current state of the transformation matrix and then applies the modification(s). It means that these modifications are cumulative.

By contrast, the setTransform transformation method first sets the currently valid transformation matrix to the default value and then executes the transform transformation. This makes it the only transformation method that allows reset all cumulated transformations and set new transformation that is not cumulated.

This method is also functional in Web panels.