Merge pull request #302 from Unity-Technologies/zxw/fix_path_metric_crash

fix path metric crash issue

com.unity.uiwidgets/Runtime/ui/painting.cs

 
         public float length(int contourIndex) {
             D.assert(contourIndex <= currentContourIndex, () => $"Iterator must be advanced before index {contourIndex} can be used.");
-            return PathMeasure_length(contourIndex);
+            return PathMeasure_length(_ptr, contourIndex);
         }
 
         public unsafe Tangent getTangentForOffset(int contourIndex, float distance) {
-                PathMeasure_getPosTan(contourIndex, distance, posTanPtr);
+                PathMeasure_getPosTan(_ptr, contourIndex, distance, posTanPtr);
             }
 
             if (posTan[0] == 0.0f) {
         public Path extractPath(int contourIndex, float start, float end, bool startWithMoveTo = true) {
             D.assert(contourIndex <= currentContourIndex,
                 () => $"Iterator must be advanced before index {contourIndex} can be used.");
-            IntPtr pathPtr = PathMeasure_getSegment(contourIndex, start, end, startWithMoveTo);
+            IntPtr pathPtr = PathMeasure_getSegment(_ptr, contourIndex, start, end, startWithMoveTo);
-            return PathMeasure_isClosed(contourIndex);
+            return PathMeasure_isClosed(_ptr, contourIndex);
-            bool next = PathMeasure_nativeNextContour();
+            bool next = PathMeasure_nativeNextContour(_ptr);
             if (next) {
                 currentContourIndex++;
             }
         static extern void PathMeasure_dispose(IntPtr ptr);
 
         [DllImport(NativeBindings.dllName)]
-        static extern float PathMeasure_length(int contourIndex);
+        static extern float PathMeasure_length(IntPtr ptr, int contourIndex);
-        static extern unsafe void PathMeasure_getPosTan(int contourIndex, float distance, float* posTan);
+        static extern unsafe void PathMeasure_getPosTan(IntPtr ptr, int contourIndex, float distance, float* posTan);
-        static extern IntPtr PathMeasure_getSegment(int contourIndex, float start, float end,
+        static extern IntPtr PathMeasure_getSegment(IntPtr ptr, int contourIndex, float start, float end,
-        static extern bool PathMeasure_isClosed(int contourIndex);
+        static extern bool PathMeasure_isClosed(IntPtr ptr, int contourIndex);
-        static extern bool PathMeasure_nativeNextContour();
+        static extern bool PathMeasure_nativeNextContour(IntPtr ptr);
     }
 
     public class ColorFilter : IEquatable<ColorFilter> {