Package org.lwjgl.opengl

Class NVShaderBufferLoad

java.lang.Object
org.lwjgl.opengl.NVShaderBufferLoad
public class NVShaderBufferLoad extends Object
Native bindings to the NV_shader_buffer_load extension.

At a very coarse level, GL has evolved in a way that allows applications to replace many of the original state machine variables with blocks of user-defined data. For example, the current vertex state has been augmented by vertex buffer objects, fixed-function shading state and parameters have been replaced by shaders/programs and constant buffers, etc. Applications switch between coarse sets of state by binding objects to the context or to other container objects (e.g. vertex array objects) instead of manipulating state variables of the context. In terms of the number of GL commands required to draw an object, modern applications are orders of magnitude more efficient than legacy applications, but this explosion of objects bound to other objects has led to a new bottleneck - pointer chasing and CPU L2 cache misses in the driver, and general L2 cache pollution.

This extension provides a mechanism to read from a flat, 64-bit GPU address space from programs/shaders, to query GPU addresses of buffer objects at the API level, and to bind buffer objects to the context in such a way that they can be accessed via their GPU addresses in any shader stage.

The intent is that applications can avoid re-binding buffer objects or updating constants between each Draw call and instead simply use a VertexAttrib (or TexCoord, or InstanceID, or...) to "point" to the new object's state. In this way, one of the cheapest "state" updates (from the CPU's point of view) can be used to effect a significant state change in the shader similarly to how a pointer change may on the CPU. At the same time, this relieves the limits on how many buffer objects can be accessed at once by shaders, and allows these buffer object accesses to be exposed as C-style pointer dereferences in the shading language.

As a very simple example, imagine packing a group of similar objects' constants into a single buffer object and pointing your program at object <i> by setting glVertexAttribI1iEXT(attrLoc, i); and using a shader as such:


 struct MyObjectType {
     mat4x4 modelView;
     vec4 materialPropertyX;
     // etc.
 };
 uniform MyObjectType *allObjects;
 in int objectID; // bound to attrLoc
 
 ...
 
 mat4x4 thisObjectsMatrix = allObjects[objectID].modelView;
 // do transform, shading, etc.

This is beneficial in much the same way that texture arrays allow choosing between similar, but independent, texture maps with a single coordinate identifying which slice of the texture to use. It also resembles instancing, where a lightweight change (incrementing the instance ID) can be used to generate a different and interesting result, but with additional flexibility over instancing because the values are app-controlled and not a single incrementing counter.

Dependent pointer fetches are allowed, so more complex scene graph structures can be built into buffer objects providing significant new flexibility in the use of shaders. Another simple example, showing something you can't do with existing functionality, is to do dependent fetches into many buffer objects:


 GenBuffers(N, dataBuffers);
 GenBuffers(1, &pointerBuffer);
 
 GLuint64EXT gpuAddrs[N];
 for (i = 0; i < N; ++i) {
     BindBuffer(target, dataBuffers[i]);
     BufferData(target, size[i], myData[i], STATIC_DRAW);
 
     // get the address of this buffer and make it resident.
     GetBufferParameterui64vNV(target, BUFFER_GPU_ADDRESS,
                               gpuaddrs[i]);
     MakeBufferResidentNV(target, READ_ONLY);
 }
 
 GLuint64EXT pointerBufferAddr;
 BindBuffer(target, pointerBuffer);
 BufferData(target, sizeof(GLuint64EXT)*N, gpuAddrs, STATIC_DRAW);
 GetBufferParameterui64vNV(target, BUFFER_GPU_ADDRESS,
                           &pointerBufferAddr);
 MakeBufferResidentNV(target, READ_ONLY);
 
 // now in the shader, we can use a double indirection
 vec4 **ptrToBuffers = pointerBufferAddr;
 vec4 *ptrToBufferI = ptrToBuffers[i];

This allows simultaneous access to more buffers than EXT_bindable_uniform (MAX_VERTEX_BINDABLE_UNIFORMS_EXT, etc.) and each can be larger than MAX_BINDABLE_UNIFORM_SIZE_EXT.

  • Field Details

    • GL_BUFFER_GPU_ADDRESS_NV

      public static final int GL_BUFFER_GPU_ADDRESS_NV
      Accepted by the pname parameter of GetBufferParameterui64vNV, GetNamedBufferParameterui64vNV.
      See Also:

    • GL_GPU_ADDRESS_NV

      public static final int GL_GPU_ADDRESS_NV
      Returned by the type parameter of GetActiveUniform.
      See Also:

    • GL_MAX_SHADER_BUFFER_ADDRESS_NV

      public static final int GL_MAX_SHADER_BUFFER_ADDRESS_NV
      Accepted by the value parameter of GetIntegerui64vNV.
      See Also:

  • Method Details

    • glMakeBufferResidentNV

      public static void glMakeBufferResidentNV(int target, int access)

    • glMakeBufferNonResidentNV

      public static void glMakeBufferNonResidentNV(int target)

    • glIsBufferResidentNV

      public static boolean glIsBufferResidentNV(int target)

    • glMakeNamedBufferResidentNV

      public static void glMakeNamedBufferResidentNV(int buffer, int access)

    • glMakeNamedBufferNonResidentNV

      public static void glMakeNamedBufferNonResidentNV(int buffer)

    • glIsNamedBufferResidentNV

      public static boolean glIsNamedBufferResidentNV(int buffer)

    • nglGetBufferParameterui64vNV

      public static void nglGetBufferParameterui64vNV(int target, int pname, long params)

    • glGetBufferParameterui64vNV

      public static void glGetBufferParameterui64vNV(int target, int pname, LongBuffer params)

    • glGetBufferParameterui64NV

      public static long glGetBufferParameterui64NV(int target, int pname)

    • nglGetNamedBufferParameterui64vNV

      public static void nglGetNamedBufferParameterui64vNV(int buffer, int pname, long params)

    • glGetNamedBufferParameterui64vNV

      public static void glGetNamedBufferParameterui64vNV(int buffer, int pname, LongBuffer params)

    • glGetNamedBufferParameterui64NV

      public static long glGetNamedBufferParameterui64NV(int buffer, int pname)

    • nglGetIntegerui64vNV

      public static void nglGetIntegerui64vNV(int value, long result)

    • glGetIntegerui64vNV

      public static void glGetIntegerui64vNV(int value, LongBuffer result)

    • glGetIntegerui64NV

      public static long glGetIntegerui64NV(int value)

    • glUniformui64NV

      public static void glUniformui64NV(int location, long value)

    • nglUniformui64vNV

      public static void nglUniformui64vNV(int location, int count, long value)

    • glUniformui64vNV

      public static void glUniformui64vNV(int location, LongBuffer value)

    • nglGetUniformui64vNV

      public static void nglGetUniformui64vNV(int program, int location, long params)

    • glGetUniformui64vNV

      public static void glGetUniformui64vNV(int program, int location, LongBuffer params)

    • glGetUniformui64NV

      public static long glGetUniformui64NV(int program, int location)

    • glProgramUniformui64NV

      public static void glProgramUniformui64NV(int program, int location, long value)

    • nglProgramUniformui64vNV

      public static void nglProgramUniformui64vNV(int program, int location, int count, long value)

    • glProgramUniformui64vNV

      public static void glProgramUniformui64vNV(int program, int location, LongBuffer value)

    • glGetBufferParameterui64vNV

      public static void glGetBufferParameterui64vNV(int target, int pname, long[] params)
      Array version of: GetBufferParameterui64vNV

    • glGetNamedBufferParameterui64vNV

      public static void glGetNamedBufferParameterui64vNV(int buffer, int pname, long[] params)
      Array version of: GetNamedBufferParameterui64vNV

    • glGetIntegerui64vNV

      public static void glGetIntegerui64vNV(int value, long[] result)
      Array version of: GetIntegerui64vNV

    • glUniformui64vNV

      public static void glUniformui64vNV(int location, long[] value)
      Array version of: Uniformui64vNV

    • glGetUniformui64vNV

      public static void glGetUniformui64vNV(int program, int location, long[] params)
      Array version of: GetUniformui64vNV

    • glProgramUniformui64vNV

      public static void glProgramUniformui64vNV(int program, int location, long[] value)
      Array version of: ProgramUniformui64vNV