GpuMemoryLimit Type alias

Describes a strategy for imposing limits upon the amount of GPU memory consumed by Tile content.

For a given view, a set of tiles is required to display its contents. As the user navigates the view by panning, rotating, zooming, etc, that set of tiles changes. Previously-displayed tiles can remain in memory for a short while so that if they are subsequently required for display again they will be immediately available. Keeping too many tiles in memory can consume excessive amounts of GPU memory; in extreme cases, more GPU memory can be consumed than is available, resulting in loss of the WebGL context, which causes all rendering to stop.

Over-consumption of GPU memory can be prevented by imposing a limit on the maximum amount that can be in use at any one time. When the limit is exceeded, the contents of Tiles that are not currently being displayed by any Viewport are discarded, freeing up memory, until the limit is satisfied or all undisplayed tiles' contents have been discarded. The least-recently-displayed tiles' contents are discarded first, under the assumption that they are the least likely to be displayed again in the near future. Contents of tiles that are currently being displayed by at least one viewport will not be discarded.

WebGL provides no direct access to the GPU, so the amount of memory actually being consumed can only be estimated based on the amount of memory requested from it; the actual amount will invariably be larger - sometimes much larger.

The number of bytes corresponding to the various limits is estimated at run-time based on whether the client is running on a mobile device or not - tighter limits are imposed on mobile devices due to their tighter resource constraints.

In addition to the memory limits, tile contents are naturally discarded after a certain length of time during which they have been displayed by no viewports based on TileAdmin.Props.tileExpirationTime.

The options are:

• "none" - no limits are imposed. Tile contents are discarded solely based on TileAdmin.Props.tileExpirationTime.
• "aggressive" - a small limit resulting in tile contents being more aggressively discarded.
• "default" - a moderate limit that strives to balance limiting memory consumption while keeping tiles likely to be displayed again in memory.
• "relaxed" - a larger limit that may be appropriate for devices equipped with ample GPU memory.
• number - an explicit limit, in number of bytes. Because of the vagaries of actual GPU memory consumption under WebGL, this should be a conservative estimate - no more than perhaps 1/4 of the total GPU memory available, depending on the device.

see TileAdmin.Props.gpuMemoryLimits to configure the limit at startup.

see TileAdmin.gpuMemoryLimit to adjust the limit after startup.

see TileAdmin.totalTileContentBytes for the current amount of GPU memory being used for tile contents.

GpuMemoryLimit = "none" | "default" | "aggressive" | "relaxed" | number

Defined in

• core/frontend/src/tile/TileAdmin.ts Line 83

Last Updated: 12 June, 2024