Boundary

This vignette demonstrates an optional downstream bridge from XGeoRTR into ggWebGL.

The ownership split stays fixed:

• XGeoRTR owns xgeo_state, embeddings, and explainable-geometry semantics
• the bridge example resolves that backend state into renderer-ready payloads
• ggWebGL owns widget construction, shaders, panel layout, hover, pan, and zoom

No XGeoRTR code is modified here. The bridge lives entirely inside the ggWebGL example layer.

The representative and multiscale scenes show how optional XGeoRTR-style renderer inputs can combine coloured explanation-state points with sparse contribution-direction arrows. Those arrows are true ggwebgl_layer_vectors() primitives rather than line segments plus decorative anchors, so the vignette exercises the same renderer-owned vector path that downstream packages can target.

Optional Dependency

XGeoRTR is an optional development ecosystem package for ggWebGL, not a CRAN dependency. Live bridge widgets are disabled during standard vignette builds and can be enabled in development by setting GGWEBGL_BUILD_OPTIONAL_BRIDGES=true before rendering this article. When the bridge is disabled or XGeoRTR is unavailable, the package still builds and this vignette degrades to documentation-only mode.

if (!build_optional_bridges) {
  cat("Optional XGeoRTR live bridge widgets are disabled for this vignette build.\n")
} else if (!bridge_available) {
  cat("XGeoRTR is unavailable, so the live bridge widgets are skipped in this vignette.\n")
} else {
  cat("XGeoRTR bridge widgets are available.\n")
}
#> Optional XGeoRTR live bridge widgets are disabled for this vignette build.

Representative Scene

This scene demonstrates class-coloured explanation points with sparse vector arrows summarising local contribution direction.

if (!bridge_available) {
  cat("Representative widget skipped.\n")
} else {
  bridge_widgets$representative
}
#> Representative widget skipped.

Multiscale Scene

This two-panel view keeps the same vector grammar while contrasting the global embedding with a local explanation panel whose viewport is the exact data-coordinate zoom of the rectangle marked in the global panel.

if (!bridge_available) {
  cat("Multiscale widget skipped.\n")
} else {
  bridge_widgets$multiscale
}
#> Multiscale widget skipped.

Attribution Scene

if (!bridge_available) {
  cat("Attribution widget skipped.\n")
} else {
  bridge_widgets$attribution
}
#> Attribution widget skipped.

Structure Scene

if (!bridge_available) {
  cat("Structure widget skipped.\n")
} else {
  bridge_widgets$structure
}
#> Structure widget skipped.

Regeneration

The example source for these widgets lives at:

source(system.file("examples", "htmlwidget", "xgeortr-bridge-gallery.R", package = "ggWebGL"))