Revert "Fix directional shadows."

This reverts commit 6789b82401.

Reason for revert: Failing CK test.

Original change's description:
> Fix directional shadows.
>
> The xy offset calculation for drawShadow was not quite correct. Rather
> than normalizing the light vector and using the xy values of that as the
> base offset value, we should scale the light vector by 1/z.
>
> See https://github.com/flutter/engine/pull/27124#issuecomment-880182653
> for more detail.
>
> Bug: skia:10781
> Change-Id: Ib69a313cb96a532f8d89644e3d69f666a184e897
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/428880
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Jim Van Verth <jvanverth@google.com>

TBR=jvanverth@google.com,bsalomon@google.com

Change-Id: Id22c2113fc1b62109975b83a0dcda5b1b16380a8
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:10781
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/428977
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>

samplecode/SampleMaterialShadows.cpp

@@ -34,7 +34,7 @@ class MaterialShadowsView : public Sample {
         fLargeRRPath.addRRect(SkRRect::MakeRectXY(SkRect::MakeXYWH(-64, -64, 128, 128), 4, 4));
         fSmallRRPath.addRRect(SkRRect::MakeRectXY(SkRect::MakeXYWH(-40, -40, 80, 80), 4, 4));
 
-        fLightPos = SkPoint3::Make(0, -700, 700);
+        fLightPos = SkPoint3::Make(0, -700, 600);
     }
 
     SkString name() override { return SkString("MaterialShadows"); }

src/core/SkDrawShadowInfo.cpp

@@ -151,8 +151,10 @@ void GetLocalBounds(const SkPath& path, const SkDrawShadowRec& rec, const SkMatr
 
         // get spot params (in device space)
         if (SkToBool(rec.fFlags & SkShadowFlags::kDirectionalLight_ShadowFlag)) {
-            SkDrawShadowMetrics::GetDirectionalParams(occluderZ, rec.fLightPos.fX, rec.fLightPos.fY,
-                                                      rec.fLightPos.fZ, rec.fLightRadius,
+            SkPoint3 lightDir = rec.fLightPos;
+            lightDir.normalize();
+            SkDrawShadowMetrics::GetDirectionalParams(occluderZ, lightDir.fX, lightDir.fY,
+                                                      lightDir.fZ, rec.fLightRadius,
                                                       &spotBlur, &spotScale, &spotOffset);
         } else {
             SkPoint devLightPos = SkPoint::Make(rec.fLightPos.fX, rec.fLightPos.fY);
@@ -170,8 +172,10 @@ void GetLocalBounds(const SkPath& path, const SkDrawShadowRec& rec, const SkMatr
 
         // get spot params (in local space)
         if (SkToBool(rec.fFlags & SkShadowFlags::kDirectionalLight_ShadowFlag)) {
-            SkDrawShadowMetrics::GetDirectionalParams(occluderZ, rec.fLightPos.fX, rec.fLightPos.fY,
-                                                      rec.fLightPos.fZ, rec.fLightRadius,
+            SkPoint3 lightDir = rec.fLightPos;
+            lightDir.normalize();
+            SkDrawShadowMetrics::GetDirectionalParams(occluderZ, lightDir.fX, lightDir.fY,
+                                                      lightDir.fZ, rec.fLightRadius,
                                                       &spotBlur, &spotScale, &spotOffset);
             // light dir is in device space, so need to map spot offset back into local space
             SkMatrix inverse;

src/core/SkDrawShadowInfo.h

@@ -68,10 +68,8 @@ inline void GetDirectionalParams(SkScalar occluderZ, SkScalar lightX, SkScalar l
                                  SkScalar* blurRadius, SkScalar* scale, SkVector* translate) {
     *blurRadius = lightRadius*occluderZ;
     *scale = 1;
-    // Max z-ratio is "max expected elevation"/"min allowable z"
-    constexpr SkScalar kMaxZRatio = 64/SK_ScalarNearlyZero;
-    SkScalar zRatio = divide_and_pin(occluderZ, lightZ, 0.0f, kMaxZRatio);
-    *translate = SkVector::Make(-zRatio * lightX, -zRatio * lightY);
+    // assumption here is that light direction is normalized
+    *translate = SkVector::Make(-occluderZ * lightX, -occluderZ * lightY);
 }
 
 // Create the transformation to apply to a path to get its base shadow outline, given the light

src/gpu/GrSurfaceDrawContext.cpp

@@ -1152,7 +1152,9 @@ bool GrSurfaceDrawContext::drawFastShadow(const GrClip* clip,
 
     SkPoint3 devLightPos = rec.fLightPos;
     bool directional = SkToBool(rec.fFlags & kDirectionalLight_ShadowFlag);
-    if (!directional) {
+    if (directional) {
+        devLightPos.normalize();
+    } else {
         // transform light
         viewMatrix.mapPoints((SkPoint*)&devLightPos.fX, 1);
     }

src/utils/SkShadowUtils.cpp

@@ -664,7 +664,9 @@ void SkBaseDevice::drawShadow(const SkPath& path, const SkDrawShadowRec& rec) {
 
     SkPoint3 zPlaneParams = rec.fZPlaneParams;
     SkPoint3 devLightPos = rec.fLightPos;
-    if (!directional) {
+    if (directional) {
+        devLightPos.normalize();
+    } else {
         viewMatrix.mapPoints((SkPoint*)&devLightPos.fX, 1);
     }
     float lightRadius = rec.fLightRadius;