SkShadowUtils Class Reference

#include <SkShadowUtils.h>

Static Public Member Functions
static void	DrawShadow (SkCanvas *canvas, const SkPath &path, const SkPoint3 &zPlaneParams, const SkPoint3 &lightPos, SkScalar lightRadius, SkColor ambientColor, SkColor spotColor, uint32_t flags=SkShadowFlags::kNone_ShadowFlag)
static bool	GetLocalBounds (const SkMatrix &ctm, const SkPath &path, const SkPoint3 &zPlaneParams, const SkPoint3 &lightPos, SkScalar lightRadius, uint32_t flags, SkRect *bounds)
static void	ComputeTonalColors (SkColor inAmbientColor, SkColor inSpotColor, SkColor *outAmbientColor, SkColor *outSpotColor)

Detailed Description

Definition at line 38 of file SkShadowUtils.h.

Member Function Documentation

ComputeTonalColors()

void SkShadowUtils::ComputeTonalColors ( SkColor  inAmbientColor, SkColor  inSpotColor, SkColor *  outAmbientColor, SkColor *  outSpotColor  )

static

Helper routine to compute color values for one-pass tonal alpha.

Parameters

inAmbientColor	Original ambient color
inSpotColor	Original spot color
outAmbientColor	Modified ambient color
outSpotColor	Modified spot color

Definition at line 478 of file SkShadowUtils.cpp.

                                                                                        {
    // For tonal color we only compute color values for the spot shadow.
    // The ambient shadow is greyscale only.
 
    // Ambient
    *outAmbientColor = SkColorSetARGB(SkColorGetA(inAmbientColor), 0, 0, 0);
 
    // Spot
    int spotR = SkColorGetR(inSpotColor);
    int spotG = SkColorGetG(inSpotColor);
    int spotB = SkColorGetB(inSpotColor);
    int max = std::max(std::max(spotR, spotG), spotB);
    int min = std::min(std::min(spotR, spotG), spotB);
    SkScalar luminance = 0.5f*(max + min)/255.f;
    SkScalar origA = SkColorGetA(inSpotColor)/255.f;
 
    // We compute a color alpha value based on the luminance of the color, scaled by an
    // adjusted alpha value. We want the following properties to match the UX examples
    // (assuming a = 0.25) and to ensure that we have reasonable results when the color
    // is black and/or the alpha is 0:
    //     f(0, a) = 0
    //     f(luminance, 0) = 0
    //     f(1, 0.25) = .5
    //     f(0.5, 0.25) = .4
    //     f(1, 1) = 1
    // The following functions match this as closely as possible.
    SkScalar alphaAdjust = (2.6f + (-2.66667f + 1.06667f*origA)*origA)*origA;
    SkScalar colorAlpha = (3.544762f + (-4.891428f + 2.3466f*luminance)*luminance)*luminance;
    colorAlpha = SkTPin(alphaAdjust*colorAlpha, 0.0f, 1.0f);
 
    // Similarly, we set the greyscale alpha based on luminance and alpha so that
    //     f(0, a) = a
    //     f(luminance, 0) = 0
    //     f(1, 0.25) = 0.15
    SkScalar greyscaleAlpha = SkTPin(origA*(1 - 0.4f*luminance), 0.0f, 1.0f);
 
    // 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
    //
    // Assuming premultiplied alpha, this means we scale the color by (C_a - S_a*C_a) and
    // set the alpha to (S_a + C_a - S_a*C_a).
    SkScalar colorScale = colorAlpha*(SK_Scalar1 - greyscaleAlpha);
    SkScalar tonalAlpha = colorScale + greyscaleAlpha;
    SkScalar unPremulScale = colorScale / tonalAlpha;
    *outSpotColor = SkColorSetARGB(tonalAlpha*255.999f,
                                   unPremulScale*spotR,
                                   unPremulScale*spotG,
                                   unPremulScale*spotB);
}

DrawShadow()

void SkShadowUtils::DrawShadow ( SkCanvas *  canvas, const SkPath &  path, const SkPoint3 &  zPlaneParams, const SkPoint3 &  lightPos, SkScalar  lightRadius, SkColor  ambientColor, SkColor  spotColor, uint32_t  flags = SkShadowFlags::kNone_ShadowFlag  )

static

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.

Parameters

canvas	The canvas on which to draw the shadows.
path	The occluder used to generate the shadows.
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).
lightPos	Generally, the 3D position of the light relative to the canvas plane. If kDirectionalLight_ShadowFlag is set, this specifies a vector pointing towards the light.
lightRadius	Generally, the radius of the disc light. If DirectionalLight_ShadowFlag is set, this specifies the amount of blur when the occluder is at Z offset == 1. The blur will grow linearly as the Z value increases.
ambientColor	The color of the ambient shadow.
spotColor	The color of the spot shadow.
flags	Options controlling opaque occluder optimizations, shadow appearance, and light position. See SkShadowFlags.

Definition at line 559 of file SkShadowUtils.cpp.

                                               {
    SkDrawShadowRec rec;
    if (!fill_shadow_rec(path, zPlaneParams, lightPos, lightRadius, ambientColor, spotColor,
                         flags, canvas->getTotalMatrix(), &rec)) {
        return;
    }
 
    canvas->private_draw_shadow_rec(path, rec);
}

GetLocalBounds()

bool SkShadowUtils::GetLocalBounds ( const SkMatrix &  ctm, const SkPath &  path, const SkPoint3 &  zPlaneParams, const SkPoint3 &  lightPos, SkScalar  lightRadius, uint32_t  flags, SkRect *  bounds  )

static

Generate bounding box for shadows relative to path. Includes both the ambient and spot shadow bounds.

Parameters

ctm	Current transformation matrix to device space.
path	The occluder used to generate the shadows.
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).
lightPos	Generally, the 3D position of the light relative to the canvas plane. If kDirectionalLight_ShadowFlag is set, this specifies a vector pointing towards the light.
lightRadius	Generally, the radius of the disc light. If DirectionalLight_ShadowFlag is set, this specifies the amount of blur when the occluder is at Z offset == 1. The blur will grow linearly as the Z value increases.
flags	Options controlling opaque occluder optimizations, shadow appearance, and light position. See SkShadowFlags.
bounds	Return value for shadow bounding box.

Returns

Returns true if successful, false otherwise.

Definition at line 572 of file SkShadowUtils.cpp.

                                                                                         {
    SkDrawShadowRec rec;
    if (!fill_shadow_rec(path, zPlaneParams, lightPos, lightRadius, SK_ColorBLACK, SK_ColorBLACK,
                         flags, ctm, &rec)) {
        return false;
    }
 
    SkDrawShadowMetrics::GetLocalBounds(path, rec, ctm, bounds);
 
    return true;
}

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The documentation for this class was generated from the following files:

• third_party/skia/include/utils/SkShadowUtils.h
• third_party/skia/src/utils/SkShadowUtils.cpp