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/*
* Copyright 2017 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef SkShadowUtils_DEFINED
#define SkShadowUtils_DEFINED
#include "SkColor.h"
#include "SkScalar.h"
#include "../private/SkShadowFlags.h"
#include <functional>
class SkCanvas;
class SkPath;
class SkResourceCache;
class SkShadowUtils {
public:
/**
* Draw an offset spot shadow and outlining ambient shadow for the given path using a disc
* light. The shadow may be cached, depending on the path type and canvas matrix. If the
* matrix is perspective or the path is volatile, it will not be cached.
*
* @param canvas The canvas on which to draw the shadows.
* @param path The occluder used to generate the shadows.
* @param zPlaneParams Values for the plane function which returns the Z offset of the
* occluder from the canvas based on local x and y values (the current matrix is not applied).
* @param lightPos The 3D position of the light relative to the canvas plane. This is
* independent of the canvas's current matrix.
* @param lightRadius The radius of the disc light.
* @param ambientAlpha The maximum alpha of the ambient shadow.
* @param spotAlpha The maxium alpha of the spot shadow.
* @param color The shadow color.
* @param flags Options controlling opaque occluder optimizations and shadow appearance. See
* SkShadowFlags.
*/
static void DrawShadow(SkCanvas* canvas, const SkPath& path, const SkPoint3& zPlaneParams,
const SkPoint3& lightPos, SkScalar lightRadius, SkScalar ambientAlpha,
SkScalar spotAlpha, SkColor color,
uint32_t flags = SkShadowFlags::kNone_ShadowFlag);
/**
* Draw an offset spot shadow and outlining ambient shadow for the given path using a disc
* light.
*
* Deprecated version with height value (to be removed when Flutter is updated).
*
* @param canvas The canvas on which to draw the shadows.
* @param path The occluder used to generate the shadows.
* @param occluderHeight The vertical offset of the occluder from the canvas. This is
* independent of the canvas's current matrix.
* @param lightPos The 3D position of the light relative to the canvas plane. This is
* independent of the canvas's current matrix.
* @param lightRadius The radius of the disc light.
* @param ambientAlpha The maximum alpha of the ambient shadow.
* @param spotAlpha The maxium alpha of the spot shadow.
* @param color The shadow color.
* @param flags Options controlling opaque occluder optimizations and shadow appearance. See
* SkShadowFlags.
*/
static void DrawShadow(SkCanvas* canvas, const SkPath& path, SkScalar occluderHeight,
const SkPoint3& lightPos, SkScalar lightRadius, SkScalar ambientAlpha,
SkScalar spotAlpha, SkColor color,
uint32_t flags = SkShadowFlags::kNone_ShadowFlag) {
SkPoint3 zPlane = SkPoint3::Make(0, 0, occluderHeight);
DrawShadow(canvas, path, zPlane, lightPos, lightRadius, ambientAlpha, spotAlpha,
color, flags);
}
/**
* Helper routine to compute scale alpha values for one-pass tonal alpha.
*
* The final color we want to emulate is generated by rendering a color shadow (C_rgb) using an
* alpha computed from the color's luminance (C_a), and then a black shadow with alpha (S_a)
* which is an adjusted value of 'a'. Assuming SrcOver, a background color of B_rgb, and
* ignoring edge falloff, this becomes
*
* (C_a - S_a*C_a)*C_rgb + (1 - (S_a + C_a - S_a*C_a))*B_rgb
*
* Since we use premultiplied alpha, this means we can scale the color by (C_a - S_a*C_a) and
* set the alpha to (S_a + C_a - S_a*C_a).
*
* @param r Red value of color
* @param g Red value of color
* @param b Red value of color
* @param a Red value of color
* @param colorScale Factor to scale color values by
* @param tonalAlpha Value to set alpha to
*/
static inline void ComputeTonalColorParams(SkScalar r, SkScalar g, SkScalar b, SkScalar a,
SkScalar* colorScale, SkScalar* tonalAlpha) {
SkScalar max = SkTMax(SkTMax(r, g), b);
SkScalar min = SkTMin(SkTMin(r, g), b);
SkScalar luminance = 0.5f*(max + min);
// We get best results with a luminance between 0.3 and 0.5, with smoothstep applied
SkScalar adjustedLuminance = (0.6f - 0.4f*luminance)*luminance*luminance + 0.3f;
// Similarly, we need to tone down the given greyscale alpha depending on how
// much color we're applying.
a -= (0.5f*adjustedLuminance - 0.15f);
*colorScale = adjustedLuminance*(SK_Scalar1 - a);
*tonalAlpha = *colorScale + a;
}
};
#endif
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