| |
| /* |
| * 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" |
| |
| // size of the precomputed bitmap filter tables for high quality filtering. |
| // Used to precompute the shape of the filter kernel. |
| // Table size chosen from experiments to see where I could start to see a difference. |
| |
| #define SKBITMAP_FILTER_TABLE_SIZE 128 |
| |
| class SkBitmapFilter { |
| public: |
| SkBitmapFilter(float width) |
| : fWidth(width), fInvWidth(1.f/width) { |
| fPrecomputed = false; |
| fLookupMultiplier = this->invWidth() * (SKBITMAP_FILTER_TABLE_SIZE-1); |
| } |
| |
| SkFixed lookup(float x) const { |
| if (!fPrecomputed) { |
| precomputeTable(); |
| } |
| int filter_idx = int(sk_float_abs(x * fLookupMultiplier)); |
| SkASSERT(filter_idx < SKBITMAP_FILTER_TABLE_SIZE); |
| return fFilterTable[filter_idx]; |
| } |
| |
| SkScalar lookupScalar(float x) const { |
| if (!fPrecomputed) { |
| precomputeTable(); |
| } |
| int filter_idx = int(sk_float_abs(x * fLookupMultiplier)); |
| SkASSERT(filter_idx < SKBITMAP_FILTER_TABLE_SIZE); |
| return fFilterTableScalar[filter_idx]; |
| } |
| |
| float width() const { return fWidth; } |
| float invWidth() const { return fInvWidth; } |
| virtual float evaluate(float x) const = 0; |
| virtual ~SkBitmapFilter() {} |
| |
| static SkBitmapFilter* Allocate(); |
| protected: |
| float fWidth; |
| float fInvWidth; |
| |
| float fLookupMultiplier; |
| |
| mutable bool fPrecomputed; |
| mutable SkFixed fFilterTable[SKBITMAP_FILTER_TABLE_SIZE]; |
| mutable SkScalar fFilterTableScalar[SKBITMAP_FILTER_TABLE_SIZE]; |
| private: |
| void precomputeTable() const { |
| fPrecomputed = true; |
| SkFixed *ftp = fFilterTable; |
| SkScalar *ftpScalar = fFilterTableScalar; |
| for (int x = 0; x < SKBITMAP_FILTER_TABLE_SIZE; ++x) { |
| float fx = ((float)x + .5f) * this->width() / SKBITMAP_FILTER_TABLE_SIZE; |
| float filter_value = evaluate(fx); |
| *ftpScalar++ = SkFloatToScalar(filter_value); |
| *ftp++ = SkFloatToFixed(filter_value); |
| } |
| } |
| }; |
| |
| class SkMitchellFilter: public SkBitmapFilter { |
| public: |
| SkMitchellFilter(float b, float c, float width=2.0f) |
| : SkBitmapFilter(width), B(b), C(c) { |
| } |
| |
| virtual float evaluate(float x) const SK_OVERRIDE { |
| x = fabsf(x); |
| 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=2.0f) |
| : SkBitmapFilter(width), alpha(a), expWidth(expf(-alpha * width * width)) { |
| } |
| |
| virtual float evaluate(float x) const SK_OVERRIDE { |
| 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 SK_OVERRIDE { |
| return SkTMax(0.f, fWidth - fabsf(x)); |
| } |
| protected: |
| }; |
| |
| class SkBoxFilter: public SkBitmapFilter { |
| public: |
| SkBoxFilter(float width=0.5f) |
| : SkBitmapFilter(width) { |
| } |
| |
| virtual float evaluate(float x) const SK_OVERRIDE { |
| return (x >= -fWidth && x < fWidth) ? 1.0f : 0.0f; |
| } |
| protected: |
| }; |
| |
| class SkHammingFilter: public SkBitmapFilter { |
| public: |
| SkHammingFilter(float width=1.f) |
| : SkBitmapFilter(width) { |
| } |
| virtual float evaluate(float x) const SK_OVERRIDE { |
| if (x <= -fWidth || x >= fWidth) { |
| return 0.0f; // Outside of the window. |
| } |
| if (x > -FLT_EPSILON && x < FLT_EPSILON) { |
| return 1.0f; // Special case the sinc discontinuity at the origin. |
| } |
| const float xpi = x * static_cast<float>(SK_ScalarPI); |
| |
| return ((sk_float_sin(xpi) / xpi) * // sinc(x) |
| (0.54f + 0.46f * sk_float_cos(xpi / fWidth))); // hamming(x) |
| } |
| }; |
| |
| class SkLanczosFilter: public SkBitmapFilter { |
| public: |
| SkLanczosFilter(float width=3.f) |
| : SkBitmapFilter(width) { |
| } |
| |
| virtual float evaluate(float x) const SK_OVERRIDE { |
| if (x <= -fWidth || x >= fWidth) { |
| return 0.0f; // Outside of the window. |
| } |
| if (x > -FLT_EPSILON && x < FLT_EPSILON) { |
| return 1.0f; // Special case the discontinuity at the origin. |
| } |
| float xpi = x * static_cast<float>(SK_ScalarPI); |
| return (sk_float_sin(xpi) / xpi) * // sinc(x) |
| sk_float_sin(xpi / fWidth) / (xpi / fWidth); // sinc(x/fWidth) |
| } |
| }; |
| |
| |
| #endif |