Class BufferUtils
This class makes it easy and safe to work with direct buffers. It is the recommended way to allocate memory to use with LWJGL.
Direct buffers
LWJGL requires that all NIO buffers passed to it are direct buffers. Direct buffers essentially wrap an address that points to off-heap memory, i.e. a native pointer. This is the only way LWJGL can safely pass data from Java code to native code, and vice-versa, without a performance penalty. It does not support on-heap Java arrays (or plain NIO buffers, which wrap them) because arrays may be moved around in memory by the JVM's garbage collector while native code is accessing them. In addition, Java arrays have an unspecified layout, i.e. they are not necessarily contiguous in memory.
Usage
When a direct buffer is passed as an argument to an LWJGL method, no data is copied. Instead, the current buffer position is added to the buffer's memory
address and the resulting value is passed to native code. The native code interprets that value as a pointer and reads or copies from it as necessary. LWJGL
will often also use the current buffer limit (via Buffer.remaining()
) to automatically pass length/maxlength arguments. This means that, just like
other APIs that use NIO buffers, the current Buffer.position()
and Buffer.limit()
at the time of the call is very important. Contrary to
other APIs, LWJGL never modifies the current position, it will be the same value before and after the call.
Arrays of pointers
In addition to the standard NIO buffer classes, LWJGL provides a PointerBuffer
class for storing pointer data in an architecture independent way.
It is used in bindings for pointer-to-pointers arguments, usually to provide arrays of data (input parameter) or to store returned pointer values (output
parameter). Also, there's the CLongBuffer
class which is similar to PointerBuffer
, but for C long
data.
Memory management
Using NIO buffers for off-heap memory has some drawbacks:
- Memory blocks bigger than
Integer.MAX_VALUE
bytes cannot be allocated. - Memory blocks are zeroed-out on allocation, for safety. This has (sometimes unwanted) performance implications.
- There is no way to free a buffer explicitly (without JVM specific reflection). Buffer objects are subject to GC and it usually takes two GC cycles to free the off-heap memory after the buffer object becomes unreachable.
An alternative API for allocating off-heap memory can be found in the MemoryUtil
class. This has none of the above drawbacks,
but requires allocated memory to be explictly freed when not used anymore.
Memory alignment
Allocations done via this class have a guaranteed alignment of 8 bytes. If higher alignment values are required, use the explicit memory management API or pad the requested memory with extra bytes and align manually.
Structs and arrays of structs
Java does not support struct value types, so LWJGL requires struct values that are backed by off-heap memory. Each struct type defined in a binding
has a corresponding class in LWJGL that can be used to access its members. Each struct class also has a Buffer
inner class that can be used to
access (packed) arrays of struct values. Both struct and struct buffer classes may be backed by direct ByteBuffer
s allocated from this class, but it
is highly recommended to use explicit memory management for performance.
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Method Summary
Modifier and TypeMethodDescriptionstatic ByteBuffer
createByteBuffer
(int capacity) Allocates a direct native-orderedByteBuffer
with the specified capacity.static CharBuffer
createCharBuffer
(int capacity) Allocates a direct native-orderCharBuffer
with the specified number of elements.static CLongBuffer
createCLongBuffer
(int capacity) Allocates aCLongBuffer
with the specified number of elements.static DoubleBuffer
createDoubleBuffer
(int capacity) Allocates a direct native-orderDoubleBuffer
with the specified number of elements.static FloatBuffer
createFloatBuffer
(int capacity) Allocates a direct native-orderFloatBuffer
with the specified number of elements.static IntBuffer
createIntBuffer
(int capacity) Allocates a direct native-orderIntBuffer
with the specified number of elements.static LongBuffer
createLongBuffer
(int capacity) Allocates a direct native-orderLongBuffer
with the specified number of elements.static PointerBuffer
createPointerBuffer
(int capacity) Allocates aPointerBuffer
with the specified number of elements.static ShortBuffer
createShortBuffer
(int capacity) Allocates a direct native-orderShortBuffer
with the specified number of elements.static void
zeroBuffer
(ByteBuffer buffer) Fills the specified buffer with zeros from the current position to the current limit.static void
zeroBuffer
(CharBuffer buffer) Fills the specified buffer with zeros from the current position to the current limit.static void
zeroBuffer
(DoubleBuffer buffer) Fills the specified buffer with zeros from the current position to the current limit.static void
zeroBuffer
(FloatBuffer buffer) Fills the specified buffer with zeros from the current position to the current limit.static void
zeroBuffer
(IntBuffer buffer) Fills the specified buffer with zeros from the current position to the current limit.static void
zeroBuffer
(LongBuffer buffer) Fills the specified buffer with zeros from the current position to the current limit.static void
zeroBuffer
(ShortBuffer buffer) Fills the specified buffer with zeros from the current position to the current limit.static <T extends CustomBuffer<T>>
voidzeroBuffer
(T buffer) Fills the specified buffer with zeros from the current position to the current limit.
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Method Details
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createByteBuffer
Allocates a direct native-orderedByteBuffer
with the specified capacity.- Parameters:
capacity
- the capacity, in bytes- Returns:
- a
ByteBuffer
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createShortBuffer
Allocates a direct native-orderShortBuffer
with the specified number of elements.- Parameters:
capacity
- the capacity, in shorts- Returns:
- a
ShortBuffer
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createCharBuffer
Allocates a direct native-orderCharBuffer
with the specified number of elements.- Parameters:
capacity
- the capacity, in chars- Returns:
- a
CharBuffer
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createIntBuffer
Allocates a direct native-orderIntBuffer
with the specified number of elements.- Parameters:
capacity
- the capacity, in ints- Returns:
- an
IntBuffer
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createLongBuffer
Allocates a direct native-orderLongBuffer
with the specified number of elements.- Parameters:
capacity
- the capacity, in longs- Returns:
- a
LongBuffer
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createCLongBuffer
Allocates aCLongBuffer
with the specified number of elements.- Parameters:
capacity
- the capacity, in memory addresses- Returns:
- a
CLongBuffer
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createFloatBuffer
Allocates a direct native-orderFloatBuffer
with the specified number of elements.- Parameters:
capacity
- the capacity, in floats- Returns:
- a FloatBuffer
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createDoubleBuffer
Allocates a direct native-orderDoubleBuffer
with the specified number of elements.- Parameters:
capacity
- the capacity, in doubles- Returns:
- a
DoubleBuffer
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createPointerBuffer
Allocates aPointerBuffer
with the specified number of elements.- Parameters:
capacity
- the capacity, in memory addresses- Returns:
- a
PointerBuffer
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zeroBuffer
Fills the specified buffer with zeros from the current position to the current limit.- Parameters:
buffer
- the buffer to fill with zeros
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zeroBuffer
Fills the specified buffer with zeros from the current position to the current limit.- Parameters:
buffer
- the buffer to fill with zeros
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zeroBuffer
Fills the specified buffer with zeros from the current position to the current limit.- Parameters:
buffer
- the buffer to fill with zeros
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zeroBuffer
Fills the specified buffer with zeros from the current position to the current limit.- Parameters:
buffer
- the buffer to fill with zeros
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zeroBuffer
Fills the specified buffer with zeros from the current position to the current limit.- Parameters:
buffer
- the buffer to fill with zeros
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zeroBuffer
Fills the specified buffer with zeros from the current position to the current limit.- Parameters:
buffer
- the buffer to fill with zeros
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zeroBuffer
Fills the specified buffer with zeros from the current position to the current limit.- Parameters:
buffer
- the buffer to fill with zeros
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zeroBuffer
Fills the specified buffer with zeros from the current position to the current limit.- Parameters:
buffer
- the buffer to fill with zeros
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