build
Packed instanced wind barbs: endpoint phase A and B only (no Timeline.dataMeld in sampling). Matches encoded raster layers: the GPU applies dataMeld each frame so timeline crossfade stays smooth without rebuilding this buffer at playback frame rate.
Layout per instance (14 floats): tileX, tileY, dirA, speedA, dirB, speedB, rgbaA, rgbaB.
Parameters
Expand the camera bounds by this many world pixels (at placement zoom) when placing grid anchors. Use 0 for barbs (fast). Use ~384 for left-anchored wind arrows so anchors just outside the viewport are still included when the quad intersects the screen; a global margin for all layers doubled grid work and slowed timeline animation.
Expand only the east edge of the horizontal viewport span by this fraction of the span (e.g. 0.05 adds 5% width on the right) so left-anchored arrows stay visible longer when panning.