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QuerySet

caution

This page is incomplete.

A QuerySet object provides an API for using asynchronous GPU queries of the following types

  • timer queries.
  • 'Occlusion'
  • 'Transform Feedback'

A QuerySet holds a number of 64 bit values.

Timer queries are available if the timestamp-query extension is available. (On WebGL 2 this is equivalent to the EXT_disjoint_timer_query_webgl2 being supported on the current browser.

Note that even when supported, timer queries can fail whenever a change in the GPU occurs that will make the values returned by this extension unusable for performance metrics, for example if the GPU is throttled mid-frame.

Usage​

Create a timestamp query set:

import {QuerySet} from '@luma.gl/core';
...
const timestampQuery = device.createQuerySet({type: 'timestamp'}});

Types​

QueryProps​

  • type: occlusion | timestamp - type of timer
  • count: number - number of query results held by this QuerySet
Query TypeUsageDescription
timestamp (RenderPass begin/end)beginRenderPass({timestampQuery: ...})Time taken by GPU to execute RenderPass commands
timestamp (ComputePass begin/end)beginComputePass({timestampQuery: ...})Time taken by GPU to execute ComputePass commands
occlusionbeginOcclusionQuery({conservative: false})Occlusion query how many fragment samples pass tests (depth, stencil, ...)
occlusionbeginOcclusionQuery({conservative: true})Same as above above, but less accurate and faster
transform-feedback (Not yet supported)beginTransformFeedbackQuery()Number of primitives that are written to transform feedback buffers.

In addition to above queries, Query object also provides getTimeStamp which returns GPU time stamp at the time this query is executed by GPU. Two sets of these methods can be used to calculate time taken by GPU for a set of GL commands.

DeviceFeatures​

timestamp-query: Whether QuerySet can be created with type timestamp.

Methods​

constructor(device: Device, props: Object)​

new Query(gl, {})

  • options.timers=false Object - If true, checks if 'TIME_ELAPSED_EXT' queries are supported

destroy()​

Destroys the WebGL object. Rejects any pending query.

  • return Query - returns itself, to enable chaining of calls.

beginTimeElapsedQuery()​

Shortcut for timer query (dependent on extension in both WebGL 1 and 2)

RenderPass​

RenderPass.beginOcclusionQuery({conservative = false})​

Shortcut for occlusion query (dependent on WebGL 2)

RenderPass.beginTransformFeedbackQuery()​

WebGL 2 only. not yet implemented.