Fix validation and pointer arithmetics

Author: seclerp

binding/Binding/SKVertices.cs

@@ -53,13 +53,13 @@ public static SKVertices CreateCopy (SKVertexMode vmode, int vertexOffset, int v
 			if (colors != null && positions.Length != colors.Length)
 				throw new ArgumentException ("The number of colors must match the number of vertices.", nameof (colors));
 
-			if (vertexOffset >= positions.Length)
+			if (vertexOffset > positions.Length)
 				throw new ArgumentException ("The vertex offset should be in bounds of vertex array.", nameof (vertexOffset));
 
 			if (vertexOffset + vertexCount >= positions.Length)
 				throw new ArgumentException ("The vertex count should be in bounds of vertex array.", nameof (vertexOffset));
 
-			if (indexOffset >= indices.Length)
+			if (indexOffset > indices.Length)
 				throw new ArgumentException ("The index offset should be in bounds of index array.", nameof (vertexOffset));
 
 			if (indexOffset + indexCount >= indices.Length)
@@ -69,7 +69,7 @@ public static SKVertices CreateCopy (SKVertexMode vmode, int vertexOffset, int v
 			fixed (SKPoint* t = texs)
 			fixed (SKColor* c = colors)
 			fixed (UInt16* i = indices) {
-				return GetObject (SkiaApi.sk_vertices_make_copy (vmode, vertexCount, p + vertexOffset, t + vertexOffset, (uint*)c + vertexOffset, indexCount, i + indexOffset));
+				return GetObject (SkiaApi.sk_vertices_make_copy (vmode, vertexCount, p + vertexOffset * sizeof(SKPoint), t + vertexOffset * sizeof(SKPoint), (uint*)c + vertexOffset * sizeof(uint), indexCount, i + indexOffset * sizeof(ushort)));
 			}
 		}