Remove tonal color from DrawShadow internals

Bug: b/71719631
Change-Id: I676c34dfe5ea9b5e184ea53dd49a8b835d4e8cb6
Reviewed-on: https://skia-review.googlesource.com/95741
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>

1 files changed, 54 insertions, 55 deletions

diff --git a/include/utils/SkShadowUtils.h b/include/utils/SkShadowUtils.h
index 9550a925b9..3eca398fb1 100644
--- a/include/utils/SkShadowUtils.h
+++ b/include/utils/SkShadowUtils.h
@@ -31,23 +31,62 @@ public:
      * @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 ambientColor  The color of the ambient shadow.
+     * @param spotColor  The color of the spot shadow.
+     * @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,
+                           SkColor ambientColor, SkColor spotColor,
+                           uint32_t flags = SkShadowFlags::kNone_ShadowFlag);
+
+    /**
+     * Deprecated version that uses one color and two alphas, and supports tonal color.
+     *
+     * 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,
+    static void DrawShadow(SkCanvas* canvas, const SkPath& path, const SkPoint3& zPlane,
                            const SkPoint3& lightPos, SkScalar lightRadius, SkScalar ambientAlpha,
                            SkScalar spotAlpha, SkColor color,
-                           uint32_t flags = SkShadowFlags::kNone_ShadowFlag);
+                           uint32_t flags = SkShadowFlags::kNone_ShadowFlag) {
+        SkColor ambientColor;
+        SkColor spotColor;
+        if (flags & SkShadowFlags::kDisableTonalColor_ShadowFlag) {
+            ambientColor = SkColorSetARGB(ambientAlpha*SkColorGetA(color), SkColorGetR(color),
+                                          SkColorGetG(color), SkColorGetB(color));
+            spotColor = SkColorSetARGB(spotAlpha*SkColorGetA(color), SkColorGetR(color),
+                                       SkColorGetG(color), SkColorGetB(color));
+        } else {
+            SkColor inAmbient = SkColorSetA(color, ambientAlpha*SkColorGetA(color));
+            SkColor inSpot = SkColorSetA(color, spotAlpha*SkColorGetA(color));
+            ComputeTonalColors(inAmbient, inSpot, &ambientColor, &spotColor);
+        }
 
-    /**
+        DrawShadow(canvas, path, zPlane, lightPos, lightRadius, ambientColor, spotColor, flags);
+    }
+
+   /**
+    * Deprecated version with height value (to be removed when Flutter is updated).
+    *
     * 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
@@ -70,56 +109,16 @@ public:
                    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;
-    }
-
+   /**
+    * Helper routine to compute color values for one-pass tonal alpha.
+    *
+    * @param inAmbientColor  Original ambient color
+    * @param inSpotColor  Original spot color
+    * @param outAmbientColor  Modified ambient color
+    * @param outSpotColor  Modified spot color
+    */
+    static void ComputeTonalColors(SkColor inAmbientColor, SkColor inSpotColor,
+                                   SkColor* outAmbientColor, SkColor* outSpotColor);
 };
 
 #endif