Unify zoom into one feature: ⌘+/⌘−/⌘0 scales both editor and preview

[schuyler]

Summary

We currently have four open zoom PRs that overlap on the same menu items and shortcuts but split into two half-features. Neither half is complete on its own, and they collide if merged together. This issue proposes consolidating them into a single "document zoom" feature: one zoom level, one key pair (⌘+ / ⌘− / ⌘0), scaling both the editor and the preview together — which is exactly what #335 originally asked for.

Implementation note: the synthesis described here is maintainer-led. #395 and #442 are starting points to build on — no further work is expected from their authors, and the Format-shortcut relocation below is part of our scope, not theirs.

Background: what the four PRs actually do

The PRs fall into two camps:

PR	Author	Model	Scales editor?	Scales preview?	Persisted?
#337	@ssstonebraker	transient per-document	yes	no (dead stub)	no
#395	@schuyler	transient per-document	yes	no (dead stub)	no
#411	@yusufm	transient per-document	yes	no (dead stub)	no
#442	@dpankros	preview-only	no	yes (works)	yes

Key finding: the "both panes" PRs don't actually zoom the preview

The three per-document PRs (#337, #395, #411) route preview scaling through MPDocument's existing scaleWebview, whose body is dead code:

CGFloat scale = [self previewScale];   // computed…
#if 0
    // Sadly, this doesn't work correctly.
    // It looks fine, but selections are offset relative to the mouse cursor.
    ...                                 // …the code that applies `scale` is #if 0'd out
#endif

That #if 0 predates all of these PRs — MacDown disabled view-transform preview scaling long ago because of a selection-offset bug. So those three PRs compute a preview scale factor and throw it away: in practice they only zoom the editor font.

#442 is the only PR that actually zooms the preview, because it sidesteps that broken path entirely and uses WebKit's setPageSizeMultiplier: (true page zoom — text, images, and layout), which doesn't have the selection-offset problem.

So the real split is:

• Add zoom keyboard shortcuts (Cmd+, Cmd-, Cmd+0) #337 / Address issue #335: Add zoom keyboard shortcuts (Cmd+Shift+=/Cmd+Shift+-) #395 / Add transient document zoom shortcuts #411 → working editor-font zoom; preview zoom is a non-functional stub.
• Add zoom controls for the preview pane #442 → working preview zoom; doesn't touch the editor.

The missing piece that makes "one key pair, both panes" finally work is replacing the dead #if 0 transform with #442's setPageSizeMultiplier: approach.

Proposed unified design

One feature, built by synthesizing the working halves rather than picking a single PR:

• One source of truth — a single, persisted zoom level (its own preference, never the editor base font), applied to every document.
• One apply method drives both panes:
  • Editor → zoomedEditorFont + applyEditorFontAndParagraphStyle (from Address issue #335: Add zoom keyboard shortcuts (Cmd+Shift+=/Cmd+Shift+-) #395). This keeps tab stops aligned at the zoomed size, survives editor-font preference changes, and avoids a full highlighter re-parse on every zoom step.
  • Preview → setPageSizeMultiplier: (from Add zoom controls for the preview pane #442), re-applied on each mainFrame finished-load (WebKit resets the multiplier on every load).
• One key pair: ⌘+ / ⌘− / ⌘0 (Zoom In / Zoom Out / Actual Size). Take the native shortcuts and relocate the colliding Format shortcuts — Highlight (⌘=), Strikethrough (⌘−), Paragraph (⌘0) — the way Add transient document zoom shortcuts #411 does, rather than retreating to ⌘⇧ variants. For the headline feature the standard keys are worth it.
• Menu validation — disable Zoom In at max, Zoom Out at min, Actual Size at 100% (using an epsilon comparison; see Add zoom keyboard shortcuts (Cmd+, Cmd-, Cmd+0) #337/Address issue #335: Add zoom keyboard shortcuts (Cmd+Shift+=/Cmd+Shift+-) #395 review).
• Toolbar dropdown (from Add zoom controls for the preview pane #442) showing the unified zoom %, with preset snap-stepping so the shortcut and the dropdown stay in sync.
• Keep previewZoomRelativeToBaseFontSize working independently, per Add Cmd+/Cmd- zoom keyboard shortcuts #335.

What to take from each PR

• Address issue #335: Add zoom keyboard shortcuts (Cmd+Shift+=/Cmd+Shift+-) #395 — editor font/paragraph helpers (applyEditorFontAndParagraphStyle, zoomedEditorFont), the lightweight apply path (no re-highlight), conflict-free menu validation, and its test suite (MPZoomTests.m, ~21 tests).
• Add zoom controls for the preview pane #442 — the working preview mechanism (setPageSizeMultiplier: + re-apply on load), the toolbar preset dropdown, and the preference/migration plumbing.
• Add transient document zoom shortcuts #411 — the snap/step polish: multiplicative stepping and fontWithDescriptor: (preserves font traits) instead of fontWithName:size:.
• Add zoom keyboard shortcuts (Cmd+, Cmd-, Cmd+0) #337 — ancestor; superseded by the above.

Decision: persisted single preference ✅

Resolved — zoom is a persisted single preference, applied to every window (Safari-style), backed by a dedicated zoom-level preference + migration (the #442 plumbing). It is deliberately not the transient per-document model, and it is not the editor base font, so it never clobbers the user's saved font (which was the original objection in #335). The level is restored on launch.

Format-shortcut relocation

⌘+ / ⌘− / ⌘0 currently collide with Format menu items — Highlight (⌘=), Strikethrough (⌘−), and Paragraph (⌘0). The headline zoom shortcuts win these keys; the Format actions get reassigned (or moved to ⌘⇧ variants). This is in scope for the unified feature itself and is maintainer-side work — not a request to any PR author.

Test plan

• Editor: font, tab stops, and paragraph style all scale; zoom survives an editor-font preference change; no highlighter re-parse per step (perf).
• Preview: setPageSizeMultiplier: applied and re-applied after each render/reload; images and text scale together.
• Bounds: clamp at 50%–300% (or chosen preset range); menu items validate at the limits; Actual Size resets.
• Shortcuts: ⌘+/⌘−/⌘0 reach zoom; relocated Format shortcuts (Highlight/Strikethrough/Paragraph) still function at their new bindings.
• Persistence: migration default (100%), value restored on launch, shared across open windows.
• Carry over MPZoomTests.m (Address issue #335: Add zoom keyboard shortcuts (Cmd+Shift+=/Cmd+Shift+-) #395) and MPPreviewZoomTests.m (Add zoom controls for the preview pane #442).

Related issues and PRs

• Related to Add Cmd+/Cmd- zoom keyboard shortcuts #335 — the original request ("zoom the editor and preview panes together"); this issue is the consolidated implementation plan for it.
• Synthesize from Address issue #335: Add zoom keyboard shortcuts (Cmd+Shift+=/Cmd+Shift+-) #395 (editor half) and Add zoom controls for the preview pane #442 (preview half) — used as starting points; no additional work expected from their authors.
• Fold in polish from Add transient document zoom shortcuts #411.
• Close Add zoom keyboard shortcuts (Cmd+, Cmd-, Cmd+0) #337 as superseded (its three review fixes are already productized in Address issue #335: Add zoom keyboard shortcuts (Cmd+Shift+=/Cmd+Shift+-) #395).
• Close Add transient document zoom shortcuts #411 as a duplicate of Address issue #335: Add zoom keyboard shortcuts (Cmd+Shift+=/Cmd+Shift+-) #395's scope once its two good ideas are folded in.

[dpankros]

no additional work expected from their authors.

@schuyler I did the preview half (#442). I'm happy to help this effort, but I'll stay out of the way if that is more efficient.

[schuyler]

Sorry I miscommunicated! I just meant I wasn’t specifically asking you to do more work than you signed up for. Patches still 100% welcome and thank you!!

…

On Tue, Jun 23, 2026 at 05:11 David Pankros ***@***.***> wrote: *dpankros* left a comment (schuyler/macdown3000#470) <#470 (comment)> no additional work expected from their authors. @schuyler <https://github.com/schuyler> I did the preview half (#442 <#442>). I'm happy to help this effort, but I'll stay out of the way if that is more efficient. — Reply to this email directly, view it on GitHub <#470?email_source=notifications&email_token=AAAOB7CUDTHF56BYFIZBFQD5BJXVXA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTINZXHEYDGOJVGY32M4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJLDGN5XXIZLSL5RWY2LDNM#issuecomment-4779039567>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAAOB7C6O2KRCQYEWURJVNL5BJXVXAVCNFSNUABGKJSXA33TNF2G64TZHMYTAOJYG4ZTGNBTHA5US43TOVSTWNBXGIZDEMRUGIZDRILWAI> . You are receiving this because you were mentioned.Message ID: ***@***.***>