Add a factory Create function to SkColorFilterImageFilter

Add a factory Create function for SkColorFilterImageFilter, and move the matrix optimization there.  This will allow the Chrome compositor to extract the optimized matrix, and potentially apply the color matrix itself, saving a buffer allocation & draw.

Committed: https://code.google.com/p/skia/source/detail?r=6152

[Stephen White, 2012-10-23 16:14:39]

PTAL

[reed1, 2012-10-24 13:02:24]

I can think of alternatives to having to add setInput. Let me know what you
think.

1. Perform the tweaks in a helper function in your constructor.

static SkImageFilter* munge_inputs(SkColorFilter* cf, SkImageFilter* input,
SkColorFilter** cfout) {
    SkScalar colorMatrix[20], inputMatrix[20];
    SkColorFilter* inputColorFilter;

    if (input && cf->asColorMatrix(colorMatrix)
              && (inputColorFilter = input->asColorFilter())
              && inputColorFilter->asColorMatrix(inputMatrix)
              && !matrix_needs_clamping(inputMatrix)) {
        SkScalar combinedMatrix[20];
        mult_color_matrix(inputMatrix, colorMatrix, combinedMatrix);
        *cfout = SkNEW_ARGS(SkColorMatrixFilter, (combinedMatrix));
        input = input->getInput(0);
    } else {
        cf->ref();
        *cfout = cf;
    }
    return input;
}

SkColorFilterImageFilter::SkColorFilterImageFilter(SkColorFilter* cf,
SkImageFilter* input)
        : INHERITED(munge_inputs(cf, input, &fColorFilter) {
}

2. Use a Factory to create a ColorFilterImageFilter, rather than a public
constructor. We take great advantage of this for Gradients, where we do a fair
amount of error checking and optimizing on the caller's inputs before deciding
what subclass to actually create.

SkImageFilter* SkColorFilterImageFilter::Create(SkColorFilter*, SkImageFilter*);

[Stephen White, 2012-10-26 19:10:29]

On 2012/10/24 13:02:24, reed1 wrote:
> I can think of alternatives to having to add setInput. Let me know what you
> think.
> 
> 1. Perform the tweaks in a helper function in your constructor.
> 
> static SkImageFilter* munge_inputs(SkColorFilter* cf, SkImageFilter* input,
> SkColorFilter** cfout) {
>     SkScalar colorMatrix[20], inputMatrix[20];
>     SkColorFilter* inputColorFilter;
> 
>     if (input && cf->asColorMatrix(colorMatrix)
>               && (inputColorFilter = input->asColorFilter())
>               && inputColorFilter->asColorMatrix(inputMatrix)
>               && !matrix_needs_clamping(inputMatrix)) {
>         SkScalar combinedMatrix[20];
>         mult_color_matrix(inputMatrix, colorMatrix, combinedMatrix);
>         *cfout = SkNEW_ARGS(SkColorMatrixFilter, (combinedMatrix));
>         input = input->getInput(0);
>     } else {
>         cf->ref();
>         *cfout = cf;
>     }
>     return input;
> }
> 
> SkColorFilterImageFilter::SkColorFilterImageFilter(SkColorFilter* cf,
> SkImageFilter* input)
>         : INHERITED(munge_inputs(cf, input, &fColorFilter) {
> }
> 
> 2. Use a Factory to create a ColorFilterImageFilter, rather than a public
> constructor. We take great advantage of this for Gradients, where we do a fair
> amount of error checking and optimizing on the caller's inputs before deciding
> what subclass to actually create.
> 
> SkImageFilter* SkColorFilterImageFilter::Create(SkColorFilter*,
SkImageFilter*);

I decided to go with the second approach (a factory function), since it seemed
cleaner.  Let me know what you think.

[reed1, 2012-10-26 19:19:59]

me like'm factories.

lgtm