Package org.lwjgl

Class BufferUtils


  • public final class BufferUtils
extends java.lang.Object

    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).

    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 ByteBuffers allocated from this class, but it is highly recommended to use explicit memory management for performance.

    • Method Summary

      All Methods Static Methods Concrete Methods 
      Modifier and Type Method and Description
      static java.nio.ByteBuffer createByteBuffer(int capacity)
      Allocates a direct native-ordered bytebuffer with the specified capacity.
      static java.nio.CharBuffer createCharBuffer(int capacity)
      Allocates a direct native-order charbuffer with the specified number of elements.
      static java.nio.DoubleBuffer createDoubleBuffer(int capacity)
      Allocates a direct native-order doublebuffer with the specified number of elements.
      static java.nio.FloatBuffer createFloatBuffer(int capacity)
      Allocates a direct native-order floatbuffer with the specified number of elements.
      static java.nio.IntBuffer createIntBuffer(int capacity)
      Allocates a direct native-order intbuffer with the specified number of elements.
      static java.nio.LongBuffer createLongBuffer(int capacity)
      Allocates a direct native-order longbuffer with the specified number of elements.
      static PointerBuffer createPointerBuffer(int capacity)
      Allocates a PointerBuffer with the specified number of elements.
      static java.nio.ShortBuffer createShortBuffer(int capacity)
      Allocates a direct native-order shortbuffer with the specified number of elements.
      static void zeroBuffer(java.nio.ByteBuffer buffer)
      Fills the specified buffer with zeros from the current position to the current limit.
      static void zeroBuffer(java.nio.CharBuffer buffer)
      Fills the specified buffer with zeros from the current position to the current limit.
      static void zeroBuffer(java.nio.DoubleBuffer buffer)
      Fills the specified buffer with zeros from the current position to the current limit.
      static void zeroBuffer(java.nio.FloatBuffer buffer)
      Fills the specified buffer with zeros from the current position to the current limit.
      static void zeroBuffer(java.nio.IntBuffer buffer)
      Fills the specified buffer with zeros from the current position to the current limit.
      static void zeroBuffer(java.nio.LongBuffer buffer)
      Fills the specified buffer with zeros from the current position to the current limit.
      static void zeroBuffer(java.nio.ShortBuffer buffer)
      Fills the specified buffer with zeros from the current position to the current limit.
      static <T extends CustomBuffer<T>>
      void      		 zeroBuffer(T buffer)
      Fills the specified buffer with zeros from the current position to the current limit.

      • Methods inherited from class java.lang.Object

        equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Method Detail

      • createByteBuffer

        public static java.nio.ByteBuffer createByteBuffer(int capacity)
        Allocates a direct native-ordered bytebuffer with the specified capacity.
        Parameters:
        capacity - The capacity, in bytes
        Returns:
        a ByteBuffer

      • createShortBuffer

        public static java.nio.ShortBuffer createShortBuffer(int capacity)
        Allocates a direct native-order shortbuffer with the specified number of elements.
        Parameters:
        capacity - The capacity, in shorts
        Returns:
        a ShortBuffer

      • createCharBuffer

        public static java.nio.CharBuffer createCharBuffer(int capacity)
        Allocates a direct native-order charbuffer with the specified number of elements.
        Parameters:
        capacity - The capacity, in chars
        Returns:
        an CharBuffer

      • createIntBuffer

        public static java.nio.IntBuffer createIntBuffer(int capacity)
        Allocates a direct native-order intbuffer with the specified number of elements.
        Parameters:
        capacity - The capacity, in ints
        Returns:
        an IntBuffer

      • createLongBuffer

        public static java.nio.LongBuffer createLongBuffer(int capacity)
        Allocates a direct native-order longbuffer with the specified number of elements.
        Parameters:
        capacity - The capacity, in longs
        Returns:
        an LongBuffer

      • createFloatBuffer

        public static java.nio.FloatBuffer createFloatBuffer(int capacity)
        Allocates a direct native-order floatbuffer with the specified number of elements.
        Parameters:
        capacity - The capacity, in floats
        Returns:
        a FloatBuffer

      • createDoubleBuffer

        public static java.nio.DoubleBuffer createDoubleBuffer(int capacity)
        Allocates a direct native-order doublebuffer with the specified number of elements.
        Parameters:
        capacity - The capacity, in doubles
        Returns:
        a DoubleBuffer

      • createPointerBuffer

        public static PointerBuffer createPointerBuffer(int capacity)
        Allocates a PointerBuffer with the specified number of elements.
        Parameters:
        capacity - The capacity, in memory addresses
        Returns:
        a PointerBuffer

      • zeroBuffer

        public static void zeroBuffer(java.nio.ByteBuffer buffer)

public static void zeroBuffer(java.nio.ShortBuffer buffer)

public static void zeroBuffer(java.nio.CharBuffer buffer)

public static void zeroBuffer(java.nio.IntBuffer buffer)

public static void zeroBuffer(java.nio.FloatBuffer buffer)

public static void zeroBuffer(java.nio.LongBuffer buffer)

public static void zeroBuffer(java.nio.DoubleBuffer buffer)
        Fills the specified buffer with zeros from the current position to the current limit.
        Parameters:
        buffer - the buffer to fill with zeros

      • zeroBuffer

        public static <T extends CustomBuffer<T>> void zeroBuffer(T buffer)
        Fills the specified buffer with zeros from the current position to the current limit.
        Parameters:
        buffer - the buffer to fill with zeros