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      1 /*
      2  * Copyright 2017 Google Inc.
      3  *
      4  * Use of this source code is governed by a BSD-style license that can be
      5  * found in the LICENSE file.
      6  */
      7 
      8 #ifndef SkDrawShadowInfo_DEFINED
      9 #define SkDrawShadowInfo_DEFINED
     10 
     11 #include "SkColor.h"
     12 #include "SkPoint.h"
     13 #include "SkPoint3.h"
     14 
     15 class SkMatrix;
     16 class SkPath;
     17 struct SkRect;
     18 
     19 struct SkDrawShadowRec {
     20     SkPoint3    fZPlaneParams;
     21     SkPoint3    fLightPos;
     22     SkScalar    fLightRadius;
     23     SkColor     fAmbientColor;
     24     SkColor     fSpotColor;
     25     uint32_t    fFlags;
     26 };
     27 
     28 namespace SkDrawShadowMetrics {
     29 
     30 static constexpr auto kAmbientHeightFactor = 1.0f / 128.0f;
     31 static constexpr auto kAmbientGeomFactor = 64.0f;
     32 // Assuming that we have a light height of 600 for the spot shadow,
     33 // the spot values will reach their maximum at a height of approximately 292.3077.
     34 // We'll round up to 300 to keep it simple.
     35 static constexpr auto kMaxAmbientRadius = 300*kAmbientHeightFactor*kAmbientGeomFactor;
     36 
     37 static inline float divide_and_pin(float numer, float denom, float min, float max) {
     38     float result = SkTPin(sk_ieee_float_divide(numer, denom), min, max);
     39     // ensure that SkTPin handled non-finites correctly
     40     SkASSERT(result >= min && result <= max);
     41     return result;
     42 }
     43 
     44 inline SkScalar AmbientBlurRadius(SkScalar height) {
     45     return SkTMin(height*kAmbientHeightFactor*kAmbientGeomFactor, kMaxAmbientRadius);
     46 }
     47 
     48 inline SkScalar AmbientRecipAlpha(SkScalar height) {
     49     return 1.0f + SkTMax(height*kAmbientHeightFactor, 0.0f);
     50 }
     51 
     52 inline SkScalar SpotBlurRadius(SkScalar occluderZ, SkScalar lightZ, SkScalar lightRadius) {
     53     return lightRadius*divide_and_pin(occluderZ, lightZ - occluderZ, 0.0f, 0.95f);
     54 }
     55 
     56 inline void GetSpotParams(SkScalar occluderZ, SkScalar lightX, SkScalar lightY, SkScalar lightZ,
     57                           SkScalar lightRadius,
     58                           SkScalar* blurRadius, SkScalar* scale, SkVector* translate) {
     59     SkScalar zRatio = divide_and_pin(occluderZ, lightZ - occluderZ, 0.0f, 0.95f);
     60     *blurRadius = lightRadius*zRatio;
     61     *scale = divide_and_pin(lightZ, lightZ - occluderZ, 1.0f, 1.95f);
     62     *translate = SkVector::Make(-zRatio * lightX, -zRatio * lightY);
     63 }
     64 
     65 // Create the transformation to apply to a path to get its base shadow outline, given the light
     66 // parameters and the path's 3D transformation (given by ctm and zPlaneParams).
     67 // Also computes the blur radius to apply the transformed outline.
     68 bool GetSpotShadowTransform(const SkPoint3& lightPos, SkScalar lightRadius,
     69                             const SkMatrix& ctm, const SkPoint3& zPlaneParams,
     70                             const SkRect& pathBounds, SkMatrix* shadowTransform, SkScalar* radius);
     71 
     72 // get bounds prior to the ctm being applied
     73 void GetLocalBounds(const SkPath&, const SkDrawShadowRec&, const SkMatrix& ctm, SkRect* bounds);
     74 
     75 }
     76 
     77 #endif
     78