Direct evaluation of gaussian

The SVG(CSS) standard allows the 3 pass algorithm for sigma >= 2. But
sigma < 2, the code must evaluate to the convolution. The old code used
an interpolation scheme between windowed filters. This code directly
evaluates the gaussian kernel for sigma < 2.

This code produces cleaner results, is 25% faster, and does not use a
temporary memory buffer.

Change-Id: Ibd0caa73cadd06b637f55ba7bd4fefcfe7ac73db
Reviewed-on: https://skia-review.googlesource.com/62540
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/src/core/SkGaussFilter.h b/src/core/SkGaussFilter.h
index 9af45c875b..be00cf2cc0 100644
--- a/src/core/SkGaussFilter.h
+++ b/src/core/SkGaussFilter.h
@@ -27,10 +27,16 @@ public:
     int radius() const { return fN - 1; }
     int width() const { return 2 * this->radius() + 1; }
 
+    // TODO: remove filterDouble and use the ranged-for loop interface.
+
     // Take an array of values where the gaussian factors will be placed. Return the number of
     // values filled.
     int filterDouble(double values[5]) const;
 
+    // Allow a filter to be used in a C++ ranged-for loop.
+    const double* begin() const { return &fBasis[0];  }
+    const double* end()   const { return &fBasis[fN]; }
+
 private:
     double fBasis[5];
     int    fN;