Blend: Smooth Color counts a step per level of color change

Smooth Color now counts the steps between each pair of keys from the
keys' colors and visible bounds, which changes the step count of most
Smooth Color blends. The counts are VectorCraft's own values:

- When the keys' solid fills or strokes differ (in groups, member by
  member; in text, run by run), the count is 255 times the largest
  change of one channel as a fraction of its range, a half step
  rounding down, from 1 to 254. An RGB channel's range is 256 values,
  CMYK and gray count in percent, and two tints of one swatch by their
  tints. It is at most eight per point of the largest of the keys'
  widths and heights and the distance between their centers. Black to
  white was 128 steps and is now 254.
- When the colors match, a solid paint meets no paint, or a key holds
  a gradient or a pattern, the count is the largest distance between
  corresponding visible bounding-box edges divided by the keys' mean
  width or height, rounded, less one, from 1 to 1000. Two 20 pt
  squares 200 pt apart were 100 steps and are now 9.

Keys without bounds make the color count when their colors differ,
and 1 step otherwise.

A blend nested in another blend's keys counts toward the step limit
by its color steps when its colors differ, and as up to 1000 steps
when they match (256 before). An outer blend of 200 steps between two
such same-color Smooth Color blends now draws 99 steps.

A Smooth Color blend in an .ai file whose drawn steps follow this rule
now opens as a live blend.

Blend Options: https://web.archive.org/web/20241217212108/https://helpx.adobe.com/illustrator/using/blending-objects.html
Docs: docs/mcp.md, docs/target-app-parity.md.

docs/mcp.md

@@ -6464,7 +6464,19 @@ shows, and so do the click-to-size dialogs (`perspective.draw` with `at`: the cl
 
 `object.blend.make` blends the selected objects (or `ids`) into a live blend. Spacing and orientation default to
 what `object.blend.options` set with no blend selected (`object.blend.info` reads them: `target: "defaults"`),
-else Smooth Color and Align to Page. `starts` gives, per object, the anchor of its first subpath the blend starts
+else Smooth Color and Align to Page. Smooth Color counts the steps between each pair of keys on its own, from the
+keys' colors and visible bounds rather than along the spine. The counts below are VectorCraft's own values. The
+colors compared are each key's solid fill and stroke, the fills and strokes of two text objects' runs at the same fraction of their characters, and
+those of two groups' members paired in order. When they differ, the count is 255 times the largest change of one
+channel as a fraction of its range, a half step rounding down, from 1 to 254. An RGB channel's range is 256 values,
+so pure red to pure blue makes 254 steps. CMYK and gray count by their percentages, two tints of the same swatch by
+their tints, and colors in different spaces (or Lab) by their RGB values over 255. The count is then at most eight
+per point of the largest of the keys' widths and heights and the distance between their centers along either axis,
+and when a key has no bounds it is the color count alone. When the colors match, a solid paint meets no paint, or a
+key holds a gradient or a pattern, the count is the largest distance between the keys' corresponding visible
+bounding-box edges divided by their mean width (left and right edges) or height (top and bottom), rounded, less one,
+from 1 to 1000. Keys with no width or no height are measured by their other side, keys with neither in points, and
+keys without bounds make 1 step. `starts` gives, per object, the anchor of its first subpath the blend starts
 from (as the Blend tool's clicks on anchor points do; an open path's last anchor runs it the other way). With the
 Blend tool, `press_key` Escape drops the object clicked first and stops the next click adding to the blend
 just made; the document and the selection stay as they are. A blend

docs/target-app-parity.md

@@ -1088,6 +1088,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
 - **Advanced art:** live Blends (steps/distance/smooth colour, editable spine, anchor-targeted Blend tool, faithful interpolation, knockout), Envelope Distort (warp/mesh/top object, Reset, full Envelope Options, mesh handles, Edit Contents; type, images, symbols, gradients, patterns and appearance distorted everywhere), Liquify tools with options and pen pressure, Puppet Warp with rotating pins, Perspective Grid with presets, movable planes and projected type (choosing a perspective tool shows the grid; Hide Grid hides it with the tool still chosen), Gradient Mesh, Shape Builder (stroke-only open paths and lines cut the regions they cross and enclose regions of their own, and regions they bound merge without seams where the lines cross at rounded coordinates (#893); filled open paths count as closed; erase mode while Alt/Option is held: a minus pointer, red highlights of what will go, a click or drag deletes the regions touched, the pieces of open lines and the edges (outline pieces between the points where paths meet, opening their paths there) it passes over, one undo step, `shapeBuilder.merge {erase}` and `shapeBuilder.regions` edges over MCP), Live Paint (every path an edge, open lines included), Image Trace (12 presets, colour layers traced in parallel; a trace past two million anchor points is refused with advice rather than running out of memory, an image over 64 megapixels is traced scaled down to that size (aspect kept, paths at the image's own size) and one over 192 megapixels is refused, and a selection too large to outline shows its bounds (#525); Object › Image Trace › Make and Make and Expand trace at once with the Default preset, #543; with an image selected the Control bar and the Properties panel show Image Trace, whose arrow traces with any preset, Mask (`object.maskImage`: a clipping path on the image's outline, selected so its handles crop), Crop Image (a crop box on the image, starting on its part over the artboard, dragged by its handles or inside it, the outside dimmed, with X/Y/W/H, Apply and Cancel in the Control bar, Enter and Escape, #734; `object.cropImage {rect}` for agents, `{trim: true}` cuts an image to its pixels that aren't fully transparent, pixel for pixel) and Embed or Unembed in place of Fill and Stroke; with an Image Trace object selected, its Preset (choosing another traces again), View, the Image Trace panel and Expand, plus Release in Properties; the five View modes (Tracing Result, with Outlines, Outlines, Outlines with Source Image, Source Image) redraw a trace on screen without tracing again, are saved with it and `imageTrace.setView` sets them, while exports and Expand keep the result; the panel's Advanced section is a header that stays open or closed as it was left (part of #641); Color mode's Palette: Limited, Full Tone (as many colours as the tones need, Less … More), Automatic (flat art with its own colours, else Full Tone; a heuristic) and Document Library (the most used colours of the document's swatches or a swatch library, filled with the swatch colours as they are), part of #641; Advanced › Create: Fills and/or Strokes, where lines up to the Stroke width trace as stroked centre lines (distance transform, thinning, a skeleton graph with spurs pruned, curve fitting; one width per line; without Fills, wider areas become stroked outlines), part of #641), pattern swatches with pattern editing mode, live Repeat (radial/grid/mirror). A single selected mirror repeat shows a prominent axis with a center move handle and two rotation handles. Drag the line or center to change spacing, or an end to change angle; Shift snaps rotation to 45°. The original artwork stays in place, the reflected copy previews live, Escape cancels and each drag takes one undo step through `object.repeat.options`. Controls follow zoom/view rotation and hide with edges or the bounding box. Engine and headless canvas regressions passed for gestures, history and visibility; native move, rotation and Escape screenshots were reviewed. [Public mirror-repeat reference](https://helpx.adobe.com/illustrator/desktop/paint-and-fill/create-and-edit-patterns/set-mirror-repeat-options.html). A single selected grid repeat shows a handle below the grid for rows, one right of it for columns and one past its bottom-right corner for both, and sliders between its first two columns and rows for the horizontal and vertical spacing; the source keeps its size, each drag is one undo step and Escape cancels it ([public grid-repeat reference](https://helpx.adobe.com/illustrator/desktop/paint-and-fill/create-and-edit-patterns/set-grid-repeat-options.html), #2691). Object › Expand turns radial, grid and mirror repeats into groups of their instances (#1765, #1756).
   Choosing the Blend tool again while it is active (its toolbar button, W or `tool.select`) finishes the blend: the object clicked first is dropped and the next click no longer adds to the blend just made, so the click after it starts a new blend ([Blending objects](https://web.archive.org/web/20241217212108/https://helpx.adobe.com/illustrator/using/blending-objects.html)).
   Window › Blend exposes easing Type, Ramp and independent color Shift through `object.blend.options`.
+  Smooth Color counts the steps of each pair of keys from their color change, or from the distance between their visible bounding-box edges when their colors match or they hold gradients or patterns ([Blend Options](https://web.archive.org/web/20241217212108/https://helpx.adobe.com/illustrator/using/blending-objects.html)); the step counts, their caps and the colors compared are VectorCraft's own.
   Envelope Options › Anti-Alias off draws an envelope's distorted images without smoothing, and Preserve Shape Using › Transparency gives each piece of a distorted image an opacity mask in its shape instead of a clipping mask ([Envelope panel options](http://web.archive.org/web/20260513013456/https://helpx.adobe.com/illustrator/desktop/manage-objects/reshape-transform-objects/envelope-panel-options.html)).
   The four polynomial distributions are original approximations of the public description, not measured
   numeric parity. See [Blend panel overview](https://helpx.adobe.com/illustrator/desktop/manage-colors/apply-transparency-and-blending/blend-panel-overview.html).