glBufferData

glBufferData: man3/glBufferData.xml

glBufferData creates a new data store for the buffer object currently bound to target. Any pre-existing data store is deleted. The new data store is created with the specified size in bytes and usage. If data is not null, the data store is initialized with data from this pointer. In its initial state, the new data store is not mapped, it has a null mapped pointer, and its mapped access is GL_READ_WRITE. usage is a hint to the GL implementation as to how a buffer object's data store will be accessed. This enables the GL implementation to make more intelligent decisions that may significantly impact buffer object performance. It does not, however, constrain the actual usage of the data store. usage can be broken down into two parts: first, the frequency of access (modification and usage), and second, the nature of that access. The frequency of access may be one of these: The nature of access may be one of these:

If data is null, a data store of the specified size is still created, but its contents remain uninitialized and thus undefined. Clients must align data elements consistent with the requirements of the client platform, with an additional base-level requirement that an offset within a buffer to a datum comprising N bytes be a multiple of N.