Tooltips and selection

Pointer reporting in 3D

Move over the sphere. The plot answers where on the surface the pointer is, in the scene's own coordinates, in the same call that asked.

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scenes/pointer-reporting-in-3d

plot.showMesh(plot.uploadMesh(extractIsosurface(field(48, 10, radial), 9)), [0.3, 0.6, 0.85]);
plot.frameScene();
// Off unless asked for: answering needs a copy of the frame's pickable
// geometry kept every frame.
plot.setScenePicking(true);
return {
  pointer(x, y) {
    const hit = plot.pickSceneNow(x, y);
    return hit ? `surface at (${hit.position.map(fixed).join(", ")})` : "nothing under the pointer";
  },
};

Calls

6 in the code above, in the order it makes them

plot.showMesh(handle: MeshHandle, colour: Colour | Hex): void

Draw the surface handle names.

plot.uploadMesh(mesh: Mesh): MeshHandle

Upload a surface and return a handle naming it.

extractIsosurface(field: Field, isovalue: number): Surface

The surface through isovalue in a scalar field, as triangles.

Nothing is uploaded and nothing is drawn. The drawn path -- Plot.uploadField and Plot.showIsosurface -- triangulates in a compute shader every frame and keeps nothing, which is what makes a dragged isovalue cost a frame rather than an upload, and also why it cannot answer a question about the surface itself. This is the path for those: an area, an intersection, a file to export.

An isovalue the field never reaches gives a surface of no triangles rather than an error, so a slider swept past the end of the range makes the surface disappear rather than fail.

plot.frameScene(): void

Point the camera at the middle of everything uploaded, far enough back to see it.

Call after uploading. A scene measured in grid cells or in millimetres is nowhere near where a camera starts, and without this the first thing a caller sees is an empty canvas.

plot.setScenePicking(on: boolean): void

Keep what a scene pick needs, from the next frame on.

Off by default: answering a pick later means keeping a copy of the frame's pickable geometry every frame, which is a cost every page would pay for something most do not use. Call it once at setup.

plot.pickSceneNow(x: number, y: number, detail?: boolean): ScenePick | null

What scene item is under a pixel, answered now.

The immediate answer and the narrow one: a CPU ray-cast, so it needs setScenePicking on and a frame drawn since, and it reaches uploaded surfaces rather than every kind of scene item. pickScene is the general one and the one to reach for; this is for the case where the answer is needed inside the same call and the scene is surfaces.