Add function to get both min and max scale factors from matrix

Add function to get both min and max scale factors from matrix

Committed: http://code.google.com/p/skia/source/detail?r=14804

[bsalomon, 2014-05-20 14:23:04]

Depends on https://codereview.chromium.org/295713002/

[reed1, 2014-05-20 15:17:55]

do we want a more detailed dox for what these values are, or how they are
computed? (e.g. how this might or might not be related to SVD or other
decompositions)?

can these be private (helper functions that take a matrix, exposed in a src/
header?

https://codereview.chromium.org/298473002/diff/40001/include/core/SkMatrix.h
File include/core/SkMatrix.h (right):

https://codereview.chromium.org/298473002/diff/40001/include/core/SkMatrix.h#...
include/core/SkMatrix.h:583: * is scaleFactors[1]. If the matrix has perspective
-1 will be returned and scaleFactors will
-1 --> false

https://codereview.chromium.org/298473002/diff/40001/include/core/SkMatrix.h#...
include/core/SkMatrix.h:586: bool getScaleFactors(SkScalar scaleFactors[2])
const;
1. do we need this entrypoint and the other two?
2. getMinMaxScaleFactors() ?

[bsalomon, 2014-05-20 15:32:41]

On 2014/05/20 15:17:55, reed1 wrote:
> do we want a more detailed dox for what these values are, or how they are
> computed? (e.g. how this might or might not be related to SVD or other
> decompositions)?

Added a comment that they are computed from the SVD of the upper left 2x2.

> 
> can these be private (helper functions that take a matrix, exposed in a src/
> header?

I suppose that could be done. These don't seem that ill-defined to me and there
are much worse offenders in this class IMO:

fixedStepInX
cheapEqualTo
writeToMemory
readFromMemory
InvalidMatrix
dirtyMatrixTypeCache
setPolyToPoly
mapRadius

https://codereview.chromium.org/298473002/diff/40001/include/core/SkMatrix.h
File include/core/SkMatrix.h (right):

https://codereview.chromium.org/298473002/diff/40001/include/core/SkMatrix.h#...
include/core/SkMatrix.h:583: * is scaleFactors[1]. If the matrix has perspective
-1 will be returned and scaleFactors will
On 2014/05/20 15:17:55, reed1 wrote:
> -1 --> false

Done.

https://codereview.chromium.org/298473002/diff/40001/include/core/SkMatrix.h#...
include/core/SkMatrix.h:586: bool getScaleFactors(SkScalar scaleFactors[2])
const;
On 2014/05/20 15:17:55, reed1 wrote:
> 1. do we need this entrypoint and the other two?
Most call sites only require 1 of the 2 and computing both can add an extra
branch and sqrt.

> 2. getMinMaxScaleFactors() ?

changed to getMinMaxScales() (to be consistent with getMinScale(),
getMaxScale())

[reed1, 2014-05-20 16:54:13]

lgtm

[bsalomon, 2014-05-20 16:56:57]

The CQ bit was checked by bsalomon@google.com

[commit-bot: I haz the power, 2014-05-20 16:57:13]

CQ is trying da patch. Follow status at
 https://skia-tree-status.appspot.com/cq/bsalomon@google.com/298473002/60001

[commit-bot: I haz the power, 2014-05-20 17:02:09]

Change committed as 14804