CesiumGS/cesium

Remove need to check ready before calling getGeometryInstanceAttributes

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#2174 opened on Oct 2, 2014

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 (5 comments) (2 reactions) (0 assignees)JavaScript (11,758 stars) (3,324 forks)batch import
category - graphicsgood first issuetype - cleanuptype - enhancement

Description

This leads to workarounds like:

var frameNumber = 0;
var scratch = new Cesium.Cartesian3();
var ready = false;

viewer.clock.onTick.addEventListener(function() {
    var length = updates.length;
    var k;
    var u;

    if (!ready && primitive.ready) {
        ready = true;
        for (k = 0; k < length; ++k) {
            u = updates[k];
            u.attributes = primitive.getGeometryInstanceAttributes(k);
        }

        return;
    }

    if (ready) {
        for (k = 0; k < length; ++k) {
            u = updates[k];
            scratch = Cesium.Cartesian3.multiplyByScalar(u.direction, (Math.sin(frameNumber * u.speed) * u.maxHeight), scratch);
            u.attributes.offset = Cartesian3InstanceAttribute.toValue(scratch, u.offsetArray);
        }
    }

    ++frameNumber;
});

Full example: https://gist.github.com/pjcozzi/4bc8fbf5a2907de6c3a9

We can just buffer the attributes, which will also eliminate the need for a scratch variable each time an attribute is set (u.offsetArray above), which caught me recently. I suspect this can be done without creating GC pressure so the performance drop should be insignificant compared to the usability gain.

CC #766

Contributor guide

Tech stack
javascript
Domain
developer experiencefrontend
Issue type
refactor
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
familiarity with Cesium APIunderstanding of geometry instances
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
45
Research direction
The issue requests removal of the 'ready' check before calling getGeometryInstanceAttributes. To implement, examine the Cesium source code for how geometry instance attributes are currently buffered (likely in the Primitive or GeometryInstance classes). The example in the issue shows a workaround; the goal is to make getGeometryInstanceAttributes wait until the primitive is ready internally. Look at the code linked in CC #766 and the gist for context. Focus on avoiding GC pressure while buffering the attributes.