Force shadow casters above the Z=0 plane

Change-Id: Ifee75414829d4bfb3c7aa6219f1f9bcfd50ff0c6

3 files changed, 13 insertions, 5 deletions

diff --git a/libs/hwui/OpenGLRenderer.cpp b/libs/hwui/OpenGLRenderer.cpp
index 83de772..879b4c7 100644
--- a/libs/hwui/OpenGLRenderer.cpp
+++ b/libs/hwui/OpenGLRenderer.cpp
@@ -3222,10 +3222,12 @@ status_t OpenGLRenderer::drawShadow(const mat4& casterTransformXY, const mat4& c
     // map 2d caster poly into 3d
     const int casterVertexCount = casterVertices2d.size();
     Vector3 casterPolygon[casterVertexCount];
+    float minZ = FLT_MAX;
     for (int i = 0; i < casterVertexCount; i++) {
         const Vertex& point2d = casterVertices2d[i];
         casterPolygon[i] = Vector3(point2d.x, point2d.y, 0);
         mapPointFakeZ(casterPolygon[i], casterTransformXY, casterTransformZ);
+        minZ = fmin(minZ, casterPolygon[i].z);
     }
 
     // map the centroid of the caster into 3d
@@ -3235,6 +3237,15 @@ status_t OpenGLRenderer::drawShadow(const mat4& casterTransformXY, const mat4& c
     Vector3 centroid3d(centroid.x, centroid.y, 0);
     mapPointFakeZ(centroid3d, casterTransformXY, casterTransformZ);
 
+    // if the caster intersects the z=0 plane, lift it in Z so it doesn't
+    if (minZ < SHADOW_MIN_CASTER_Z) {
+        float casterLift = SHADOW_MIN_CASTER_Z - minZ;
+        for (int i = 0; i < casterVertexCount; i++) {
+            casterPolygon[i].z += casterLift;
+        }
+        centroid3d.z += casterLift;
+    }
+
     // draw caster's shadows
     if (mCaches.propertyAmbientShadowStrength > 0) {
         paint.setARGB(casterAlpha * mCaches.propertyAmbientShadowStrength, 0, 0, 0);
diff --git a/libs/hwui/ShadowTessellator.h b/libs/hwui/ShadowTessellator.h
index 120774b..c558460 100644
--- a/libs/hwui/ShadowTessellator.h
+++ b/libs/hwui/ShadowTessellator.h
@@ -54,6 +54,8 @@ namespace uirenderer {
 // The total number of indices used for drawing the shadow geometry as triangle strips.
 #define SHADOW_INDEX_COUNT (2 * SHADOW_RAY_COUNT + 1 + 2 * (SHADOW_RAY_COUNT + 1))
 
+#define SHADOW_MIN_CASTER_Z 0.001f
+
 class ShadowTessellator {
 public:
     static void tessellateAmbientShadow(const Vector3* casterPolygon,
diff --git a/libs/hwui/SpotShadow.cpp b/libs/hwui/SpotShadow.cpp
index 4e52555..8538b29 100644
--- a/libs/hwui/SpotShadow.cpp
+++ b/libs/hwui/SpotShadow.cpp
@@ -548,11 +548,6 @@ void SpotShadow::computeSpotShadow(const Vector3* lightPoly, int lightPolyLength
     // Validate input, receiver is always at z = 0 plane.
     bool inputPolyPositionValid = true;
     for (int i = 0; i < polyLength; i++) {
-        if (poly[i].z <= 0.00001) {
-            inputPolyPositionValid = false;
-            ALOGW("polygon below the surface");
-            break;
-        }
         if (poly[i].z >= lightPoly[0].z) {
             inputPolyPositionValid = false;
             ALOGW("polygon above the light");