Describe pixel exact zoom steps in scene and game view

Concepts.md

@@ -52,7 +52,9 @@ The camera's `zoom` magnifies the world on top: a 640x360 camera at zoom 2 shows
 units, and at 100% still fills 640x360 screen pixels. Auto and Fit name the factor they came to
 (`Auto · 100%`, `Fit · 105%`) and follow the view when it changes size. A picture larger than
 the view is cut to it, the camera stays in the middle.
-Fixed steps start on a whole screen pixel, so pixel art at 100% stays sharp. The choice belongs
+Fixed steps start on a whole screen pixel, so pixel art at 100% stays sharp. The steps count
+**device** pixels: with Windows display scaling at 125%, 100% is still one screen pixel per camera
+pixel, and Fit then names the factor in screen pixels (`Fit · 156%`). The choice belongs
 to this browser, like *Play starts*, and is not saved in the project.
 
 **Toolbar and panels.** The toolbar carries five **icon buttons** and no captions (#183): the

Keyboard.md

@@ -12,6 +12,7 @@ step-1 field lands on whole numbers), `↑`/`↓` step, shown with at most three
 and every tab), the value itself is kept at that precision — fields that are integral by nature
 (frame rectangles, the slice dialog, a camera's view size, font size, the key-repeat
 milliseconds, the index and count ports of list and text nodes) set `NumberField`'s
-`decimals: 0` and round to whole numbers · viewport: wheel zooms,
+`decimals: 0` and round to whole numbers · viewport: wheel zooms in whole steps (1/8, 1/4, 1/2,
+then 1 to 6, 8, 12, 16, 24 screen pixels per world pixel; see [Scene editing](Scene-editing)),
 middle-drag or `Shift`+drag pans, drag on empty space rubber-bands, `Ctrl`/`Shift`-click toggles an
 object in the selection (hierarchy rows too) · tilemap panel: holding `Alt` switches to Pick – a click takes that cell's tile from the active layer – and releasing it brings back the tool before ([Tilemaps](Tilemaps)) · Vector art tab: `Alt`-click a point to make it symmetric and straight again, double-click takes it away, `Esc` ends the line the Pen is drawing, `Delete` removes the selected shape ([Vector art](Vector-Art)).

Scene-editing.md

@@ -9,6 +9,15 @@ a placement the drop then denies). Picking a container up selects it, but the Co
 Dragging is the only way to place: a double-click on an asset opens its tab (a scene also becomes
 the active one), it never places.
 
+**Zoom in whole steps.** The wheel in the Scene and Container tabs and in the animation preview
+moves the zoom one step at a time: 1/8, 1/4, 1/2, then 1 to 6, 8, 12, 16 and 24 screen pixels per
+world pixel. A mouse notch is one step, a trackpad takes one every 50 pixels of scrolling. *Fit* rounds
+down to the step that still fits. The steps count **device** pixels, so zoom 1 stays one screen
+pixel per world pixel even with Windows display scaling at 125% or 150%. With every texel getting
+the same number of screen pixels, pixel art never shows one pixel wider than its neighbour,
+wherever the view is panned. Sprites that are turned or scaled by an odd factor still cannot
+be even.
+
 **Editor symbols are always on top.** The viewport draws scene content (sprites) in an
 `objects` layer and editor symbols (camera icon, labels) in an `overlay` layer above it, so a
 sprite can never hide a symbol regardless of z or hierarchy order. A viewport label keeps a