feat(layers): add getPixelOffset prop to ScatterplotLayer

[officialasishkumar]

Closes #10057

Change List

• Add getPixelOffset accessor prop to ScatterplotLayer that shifts the rendered circle by a fixed number of screen pixels, independently of zoom level
• New instance attribute instancePixelOffset (vec2, transition-enabled) with a default value of [0, 0] for full backward compatibility
• In billboard mode, the pixel offset is added to the screen-space offset before clip-space projection
• In non-billboard mode, the pixel offset is converted to common space via project_pixel_size and added to the common-space offset
• Both GLSL and WGSL shader variants are updated
• Follows the same implementation pattern as IconLayer and TextLayer

Usage

new ScatterplotLayer({
  data,
  getPosition: d => d.position,
  getRadius: 100,
  getPixelOffset: [10, -5],  // shift 10px right, 5px up
})

[missx-oai]

@officialasishkumar Can you share your use case for this feature?

[officialasishkumar]

@missx-oai The use case is screen-space nudging for circles that share the same geographic anchor without altering the underlying coordinates. That is useful for decluttering overlapping scatterplot markers and for aligning a circle with nearby text or icon layers that already support pixel offsets.

[officialasishkumar]

Will resolve the merge conflicts

[Pessimistress]

Please update the documentation for ScatterplotLayer.

[coveralls]

coverage: 81.456%. remained the same — officialasishkumar:feat/scatterplot-pixel-offset into visgl:master

[officialasishkumar]

Updated the ScatterplotLayer documentation with the getPixelOffset accessor, following the same format used in IconLayer and TextLayer docs. Also rebased on latest master and resolved the merge conflict in the WGSL shader.