Atomic Counter/Layout Parameters

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Revision as of 12:18, 5 June 2013 by Alfonse (talk | contribs) (Clarification.)

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Atomic counters use two layout qualifier parameters. The binding​ defines which Buffer Object bound to the given index in the indexed target GL_ATOMIC_COUNTER_BUFFER​ will provide the storage for this atomic counter. The binding​ parameter is not optional.

Atomic counters also have an optional offset​ parameter. The offset is the byte offset from the beginning of the range bound to the target to the location where this variable gets its 32-bits of storage.

The offset​ parameter is not required. If it is not specified, then the offset​ will be 4 bytes larger than the offset previously used for that binding​, starting at 0 if none were previously specified. For example:

layout(binding = 0, offset = 12) uniform atomic_uint one;
layout(binding = 0) uniform atomic_uint two;
layout(binding = 0, offset = 4) uniform atomic_uint three;

layout(binding = 1) uniform atomic_uint four;
layout(binding = 1) uniform atomic_uint five;
layout(binding = 1, offset = 20) uniform atomic_uint six;
layout(binding = 0) uniform atomic_uint seven;

The offsets for these are as follows:

  • one​: 12
  • two​: 16 (12 + 4)
  • three​: 4 (specified)
  • four​: 0 (unused bindings offsets always start with a default of 0).
  • five​: 4
  • six​: 20
  • seven​: 8 (the last value used for binding 0 was 4, so this one gets 8).