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renderingdirectxgeometry-instancing
Gregor Sattel
Gregor Sattel

Reputation: 400

DirectX - when to use instancing and when not?

I'm making an application using directx 11. I wanted to make use of instancing in the first place, so I've organized my whole pipeline to always work with instancing for simplicity. This means that currently if I want to draw a single occurrence of a geometry in my scene it would still go through instanced rendering.

My question(s) is(are) what overhead does instancing introduce? Is this approach a bad practice in general? If so, is there a rule on how to decide when it's beneficial to use instancing and when not?

One similar question that did not help me: What overhead is associated with instanced rendering?

Upvotes: 2

Views: 978

Answers (1)

Chuck Walbourn
Chuck Walbourn

Reputation: 41022

Over the years the "knee" in the performance graph of when hardware instancing is a win vs. just drawing multiple times has changed. In the early days of hardware instancing, it was almost never a win on those first generation cards. As GPU's have evolved and put more hardware support in to make this faster, it's improved significantly.

For DirectX 12 class hardware (minimum Direct3d Hardware Feature level 11.0), you can count on instancing being a good win for drawing the same objects thousands of times. If you are talking about tens of times, then it's going to depend on many factors you can really only account for by running performance trials.

Specifically for 'point-sprites' i.e. particles systems for special effects, there are a number of different approaches. For Xbox One class GPU hardware, just drawing a bunch for vertices is very fast and vertex hardware instancing only wins over it for huge numbers of particles (although it will use less VRAM so that may be a consideration). For "DirectX 12 Ultimate" class GPU hardware, a Mesh Shader is actually the fastest way to draw particle systems. See the PointSprites sample on GitHub.

Upvotes: 7

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