updatePositions method
Replaces every vertex position, keeping the vertex count unchanged.
positions holds three floats per vertex and must match the
current vertexCount. To change the vertex count, use rebuild.
Throws a StateError unless this geometry is
GeometryStorage.updatable.
Implementation
void updatePositions(Float32List positions) {
_ensureUpdatable('updatePositions');
_checkAttributeLength('positions', positions.length, 3);
_cpuPositions = Float32List.fromList(positions);
_uploadVertexBytes();
_recomputeBounds();
}