TransformationMatrix::multiply() does a multRight with the supplied matrix. The other operations, like scale(), are applied to the left (as expected).
I think TransformationMatrix needs explicit multLeft and multRight (or pre- and post-multiply).
I don't think it's really necessary to have both variants. This is usually provided as an optimization, since the operation is self-modifying. Today, if you wanted to multiply b * a, but put the result in a, you would have to:
TransformationMatrix tmp = b;
a = tmp.multiply(a);
Which isn't that bad. Alternatively, we could change to a non-destructive multiply, which would ALWAYS be more inefficient, rather than just when you need to flip the operation order. I don't think our use of TransformationMatrix is extensive enough to warrant this.
We have determined that SVGMatrix's multiply() is a multRight(), which also does not match its scale() etc, and indeed we think that TransformationMatrix should be more explicit about left vs. right multiply.
Now multiply() does a multRight() in TransformationMatrix, CSSMatrix and SVGMatrix. I think we should leave it that way for compatibility and add a multLeft() function (at least to TransformationMatrix and CSSMatrix).
I'm ready and willing to hack - does anyone care to mentor me through this and Bug 16062? Is there a good IRC channel to ask questions?
Find me (smfr) on #webkit later today.
In looking at the source, TransformationMatrix now has an explicit multLeft() and a multiply(), which does a multRight. This was done by cmarrin for Bug 6868 and landed r40761.
I will fix SVGMatrix's incorrect matrix multiplication as part of Bug 16062.
Is there anything left to do for this bug?
smfr: I think this bug can be closed, do you agree?