More general version of image filtering; reworked to be robust and easier to SSE

src/core/SkBitmapFilter.h

+
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+
+#ifndef SkBitmapFilter_DEFINED
+#define SkBitmapFilter_DEFINED
+
+#include "SkMath.h"
+
+class SkBitmapFilter {
+  public:
+      SkBitmapFilter( float width )
+      : fWidth( width ), fInvWidth( 1.f/width ) {
+      }
+      
+      float width() const { return fWidth; }
+      float invWidth() const { return fInvWidth; }
+      virtual float Evaluate( float x ) const = 0;

[reed1, 2013/06/18 20:21:21]

non-static methods are lowerCamelCase

[humper, 2013/06/19 20:49:26]

Done.

+  protected:
+      float fWidth;
+      float fInvWidth;
+};
+
+class SkMitchellFilter: public SkBitmapFilter {
+  public:
+      SkMitchellFilter( float b, float c, float width=2.0 )
+      : SkBitmapFilter( width ), B( b ), C( c ) { 
+      }
+      
+      virtual float Evaluate( float x ) const {

[reed1, 2013/06/18 20:21:21]

SK_OVERRIDE

[humper, 2013/06/19 20:49:26]

Done.

+          x = fabsf(x);
+          float ret;
+          if (x > 2.f) {
+              return 0;
+          } else if (x > 1.f) {
+              return ((-B - 6*C) * x*x*x + (6*B + 30*C) * x*x +
+                      (-12*B - 48*C) * x + (8*B + 24*C)) * (1.f/6.f);
+          } else {
+              return ((12 - 9*B - 6*C) * x*x*x +
+                      (-18 + 12*B + 6*C) * x*x +
+                      (6 - 2*B)) * (1.f/6.f);
+          }
+      }
+  protected:
+      float B, C;
+};
+
+class SkGaussianFilter: public SkBitmapFilter {
+  public:
+      SkGaussianFilter( float a, float width=2.0 )
+      : SkBitmapFilter( width ), alpha(a), expWidth( expf(-alpha * width * width )) { 
+      }
+      
+      virtual float Evaluate( float x ) const {
+          return SkTMax(0.f, float(expf(-alpha*x*x) - expWidth));
+      }
+  protected:
+      float alpha, expWidth;
+};
+
+class SkTriangleFilter: public SkBitmapFilter {
+  public:
+      SkTriangleFilter( float width=1 )
+      : SkBitmapFilter( width ) { 
+      }
+      
+      virtual float Evaluate( float x ) const {
+          return SkTMax( 0.f, fWidth - fabsf(x) );
+      }
+  protected:
+};
+
+class SkBoxFilter: public SkBitmapFilter {
+  public:
+      SkBoxFilter( float width=.5 )

[reed1, 2013/06/18 20:21:21]

need .5f to avoid warning

[humper, 2013/06/19 20:49:26]

Done.

+      : SkBitmapFilter( width ) { 
+      }
+      
+      virtual float Evaluate( float x ) const {
+          return 1;
+      }
+  protected:
+};
+
+
+class SkSincFilter: public SkBitmapFilter {
+  public:
+      SkSincFilter( float t, float width=3 )
+      : SkBitmapFilter( width ), tau(t) { 
+      }
+      
+      virtual float Evaluate( float x ) const {
+          x = fabsf(x/fWidth);

[reed1, 2013/06/18 20:21:21]

sk_float_abs

[reed1, 2013/06/18 20:21:21]

x * fInvWidth

[humper, 2013/06/19 20:49:26]

Done.

[humper, 2013/06/19 20:49:26]

Done.

[humper, 2013/06/19 20:49:26]

Done.

+          if (x < 1e-5) return 1.f;

[reed1, 2013/06/18 20:21:21]

1e-5f for warning I think

[humper, 2013/06/19 20:49:26]

Done.

+          if (x > 1.)   return 0.f;
+          x *= M_PI;
+          float sinc = sinf(x) / x;

[reed1, 2013/06/18 20:21:21]

sk_float_sin

[humper, 2013/06/19 20:49:26]

Done.

+          float lanczos = sinf(x * tau) / (x * tau);
+          return sinc * lanczos;
+      }
+  protected:
+      float tau;
+};
+
+
+#endif