| |
| /* |
| * 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 "SkPoint3.h" |
| #include "SkScalar.h" |
| #include "../private/SkShadowFlags.h" |
| |
| class SkCanvas; |
| class SkPath; |
| class SkResourceCache; |
| |
| class SK_API 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 Green value of color |
| * @param b Blue value of color |
| * @param a Alpha 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 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*a)*a)*a; |
| 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(a*(1 - 0.4f*luminance), 0.0f, 1.0f); |
| |
| *colorScale = colorAlpha*(SK_Scalar1 - greyscaleAlpha); |
| *tonalAlpha = *colorScale + greyscaleAlpha; |
| } |
| |
| }; |
| |
| #endif |