How should I handle sprite anchors, visible bounds, and base footprints in a React Native Skia isometric editor?

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Hi! I’m building an isometric room decoration/editor screen in React Native using React Native Skia, Reanimated, Gesture Handler, and Zustand.

I have a 30x30 isometric grid and draggable furniture sprites. Each furniture item is rendered as an image, but the image has transparent padding around the actual visible object.

The problem is that the sprite render box, the visible furniture pixels, and the base footprint do not share the same anchor.

I’m trying to separate these concepts:

1. sprite render box
2. touch / drag hitbox
3. visible alpha bounds
4. visible bottom center
5. base footprint polygon
6. collision footprint
7. boundary check against the isometric floor polygon

Right now I have:

• rectangular tile footprint for collision
• visualBounds metadata
• selectionBounds metadata
• visibleAnchorOffset metadata
• a DEV overlay for an isoFootprint polygon
• a 30x30 snap grid
• drag-to-move with Gesture Handler / Reanimated

The issue:
My DEV overlay can show a base polygon, but it is still based on metadata, not on the actual visible base of the furniture image. Because the asset has transparent padding, the sprite box bottom-center is not the same as the actual furniture bottom-center.

Question:
For an isometric furniture placement editor, what is the recommended architecture?

Should the placement anchor be based on:

A. sprite box bottom-center,
B. visible alpha bounds bottom-center,
C. manually defined base footprint polygon,
D. or a combination of visible bounds + per-category base footprint presets?

Also, for boundary checks, is it better to test:

• the anchor point only,
• the four corners of the base footprint polygon,
• the edge midpoints,
• or the full polygon against the floor polygon?

I’m especially interested in how to handle transparent-padded sprites and furniture images whose visible base does not match the image canvas.

Any advice, architecture suggestions, or example TypeScript / React Native Skia code would be appreciated.