demo: Add a unit test for computeSphereBounds

We validate that the points and radii are used correctly and produce
reasonable results. Note that the axis aligned tetrahedron is a
suboptimal input for Ritter's algorithm but slightly adjusting the radii
makes it pick a good estimate.

Author: zeux

demo/tests.cpp

@@ -1059,6 +1059,36 @@ static void clusterBoundsDegenerate()
 	assert(bounds2.center[2] - bounds2.radius <= 0 && bounds2.center[2] + bounds2.radius >= 1);
 }
 
+static void sphereBounds()
+{
+	const float vbr[] = {
+	    0, 0, 0, 0,
+	    0, 1, 0, 1,
+	    0, 0, 1, 2,
+	    1, 0, 1, 3, // clang-format
+	};
+
+	// without the radius, the center is somewhere inside the tetrahedron
+	// note that we currently compute a somewhat suboptimal sphere here due to the tetrahedron being perfecly axis aligned
+	meshopt_Bounds bounds = meshopt_computeSphereBounds(vbr, 4, sizeof(float) * 4, NULL, 0);
+	assert(bounds.radius < 0.97f);
+
+	// forcing a better initial guess for the center by using different radii produces a close to optimal sphere
+	float eps[4] = {1e-3f, 2e-3f, 3e-3f, 4e-3f};
+	meshopt_Bounds boundse = meshopt_computeSphereBounds(vbr, 4, sizeof(float) * 4, eps, sizeof(float));
+	assert(fabsf(boundse.center[0] - 0.5f) < 1e-2f);
+	assert(fabsf(boundse.center[1] - 0.5f) < 1e-2f);
+	assert(fabsf(boundse.center[2] - 0.5f) < 1e-2f);
+	assert(boundse.radius < 0.87f);
+
+	// when using the radius, the last sphere envelops the entire set
+	meshopt_Bounds boundsr = meshopt_computeSphereBounds(vbr, 4, sizeof(float) * 4, vbr + 3, sizeof(float) * 4);
+	assert(fabsf(boundsr.center[0] - 1.f) < 1e-2f);
+	assert(fabsf(boundsr.center[1] - 0.f) < 1e-2f);
+	assert(fabsf(boundsr.center[2] - 1.f) < 1e-2f);
+	assert(fabsf(boundsr.radius - 3.f) < 1e-2f);
+}
+
 static void meshletsEmpty()
 {
 	const float vbd[4 * 3] = {};
@@ -2256,6 +2286,7 @@ void runTests()
 	encodeFilterExpClamp();
 
 	clusterBoundsDegenerate();
+	sphereBounds();
 
 	meshletsEmpty();
 	meshletsDense();