GoFish Graphics
Internals
Draft. This essay is a stub or a work in progress — read it as a sketch, not settled documentation.

Fixed Aspect Ratio ​

Some marks must keep a fixed width-to-height ratio — a circular pie needs aspectRatio: 1 no matter what the data encodes. This essay will explain how aspect-ratio locking interacts with data-driven sizing during the layout pass.

Two distinct mechanisms sit nearby and must not be confused — only the first is "aspect ratio":

  • Mark-level aspect ratio (rect/ellipse aspectRatio: number, a w/h ratio): locks one mark's box shape, transferring the size-request slope across axes at space-resolution time. Per-mark, the planned subject below. (A graphic-box aspect ratio — fixing the rendered frame's w:h — is the natural future home for the same aspectRatio name; tracked separately.)
  • Chart-level equal scale (#582) — not aspect ratio: when x and y carry the same unit of measure, their data→pixel scales are equated so one data unit measures the same on both axes — circles stay circular, a 45° line looks 45°. This is not an aspectRatio knob: it follows from measure equality (field(name, measure) on both axes), the same type rule the circle mark uses. It is the "scale-level coupling" of design: what may set a size (option 3), implemented at the root scope in gofish.tsx (see the layout passes): spaceMeasure(x) === spaceMeasure(y) triggers min(...) + centering of the slack axis. It is a single-coordinate-space coupling and does not reach sizes solved in separate nested operator scopes (e.g. a packed unit mosaic).

Planned contents ​

  • The aspectRatio property on rect and ellipse.
  • How layout enforces w = h * aspectRatio while still respecting data encodings.
  • Where chart templates set aspectRatio (e.g. circular charts).
  • Failure modes and edge cases when a ratio conflicts with a size domain.
  • How it differs from chart-level equal scale above (box shape, set explicitly, vs. scale equality, derived from a shared measure).

Source ​

Likely covers:: packages/gofish-graphics/src/ast/shapes/rect.tsx, packages/gofish-graphics/src/ast/shapes/ellipse.tsx. Add the covers: frontmatter when writing this up, then run pnpm --filter docs sync-backlinks.