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perf(drawer): composite same cylindrical projections without reprojecting - #47
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…ojecting The SVG tile compositor sent every output pixel through the drawer's inverse projection and the tile source's forward projection, even when both are Mercator. Mercator on Mercator differs only by a longitude shift, so each pixel now maps to the tiles by a shift and a scale. Any other projection still takes the round trip. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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The direct path was Mercator-only. It's really a property of the projection: an equator-aligned cylindrical projection puts x at `longitudeScale × (λ − reference.x)` and y on latitude alone, so two of the same type differ by a scale and a shift of x. `Projection` gains an optional `longitudeScale` (Mercator, Gall–Peters, Equirectangular) and `cylindricalTransform(to:)`. Both the tile and the single-image samplers use it, so an equirectangular map of an equirectangular Blue Marble skips the round trip too. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
So callers that take a projection by name (GeoLogicKit, Lambdaroni's MCP tools) can list the modes and look one up without a mirror enum. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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init(reference:phiOne:) converted phiOne from degrees for project and inverse, but computed projectionSize from the degree value, so any non-zero standard parallel gave the wrong width (negative for 60°). The Cassini example also converted its value to radians before passing it in, so it was converted twice; it passes degrees now. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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…ting (#47) - Projection gains an optional `longitudeScale` (Mercator, Gall–Peters, Equirectangular) and `cylindricalTransform(to:)` - Tile and single-image samplers scale and shift instead of the inverse/forward round trip when map and raster share a cylindrical projection, e.g. Mercator tiles on a Mercator map - ProjectionMode is CaseIterable - Equirectangular's width uses its standard parallel in radians; the Cassini example no longer converts it twice Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Stacked on #46. Part of letting Maparoni's street tiles render in any projection (maparoni/lambdaroni#290). Once other projections reproject the tiles, a map in the tiles' own projection should still lay them down as they are.
Since #45, both raster samplers send every output pixel through the drawer's
inverseand then the source's forward projection. That applies to Mercator tiles on a Mercator map too.An equator-aligned cylindrical projection puts
x = k·(λ − λ₀), withydepending on latitude alone. Two projections of the same type therefore differ only by a scale and a shift ofx.Projectiongains an optionallongitudeScale, which isk. Mercator, Gall–Peters and Equirectangular have one, and every other projection hasnil.cylindricalTransform(to:)returns the scale and shift between two projections of the same type.ProjectionModealso becomesCaseIterable, so GeoLogicKit can list the modes without a mirror enum (maparoni/GeoLogicKit#244).The tests check the transform against
projectfor all three projections, with mixed centre longitudes andphiOnevalues. They also compare direct and round-trip pixels for both samplers, on zoomed, re-centred maps across the antimeridian. Bilinear sampling gives identical pixels. Nearest sampling can differ on one row, where pixel centres land exactly on a source pixel edge and the round trip'slogandatanround the other way.Testing:
swift test. No manual steps. The Lambdaroni PR covers end-to-end renders on dev.🤖 Generated with Claude Code