demo: Add a basic unit test for partitioning

This simply validates that we can partition a 2x2 cluster grid in 1, 2
or 4 partitions.

Author: zeux

demo/tests.cpp

@@ -1084,6 +1084,33 @@ static void meshletsSparse()
 	assert(memcmp(tri1, ibd + 3, 3 * sizeof(unsigned int)) == 0);
 }
 
+static void partitionBasic()
+{
+	// 0   1   2
+	//     3
+	// 4 5 6 7 8
+	//     9
+	// 10 11  12
+	const unsigned int ci[] = {
+	    0, 1, 3, 4, 5, 6,   //
+	    1, 2, 3, 6, 7, 8,   //
+	    4, 5, 6, 9, 10, 11, //
+	    6, 7, 8, 9, 11, 12, //
+	};
+
+	const unsigned int cc[4] = {6, 6, 6, 6};
+	unsigned int part[4];
+
+	assert(meshopt_partitionClusters(part, ci, sizeof(ci) / sizeof(ci[0]), cc, 4, 13, 1) == 4);
+	assert(part[0] == 0 && part[1] == 1 && part[2] == 2 && part[3] == 3);
+
+	assert(meshopt_partitionClusters(part, ci, sizeof(ci) / sizeof(ci[0]), cc, 4, 13, 2) == 2);
+	assert(part[0] == 0 && part[1] == 0 && part[2] == 1 && part[3] == 1);
+
+	assert(meshopt_partitionClusters(part, ci, sizeof(ci) / sizeof(ci[0]), cc, 4, 13, 4) == 1);
+	assert(part[0] == 0 && part[1] == 0 && part[2] == 0 && part[3] == 0);
+}
+
 static size_t allocCount;
 static size_t freeCount;
 
@@ -2142,6 +2169,8 @@ void runTests()
 	meshletsDense();
 	meshletsSparse();
 
+	partitionBasic();
+
 	customAllocator();
 
 	emptyMesh();