fix(pdf-server): translucent highlights, pinch to/from fullscreen, toolbar layout (#587)

* fix(pdf-server): translucent highlights, pinch to/from fullscreen, toolbar layout

Highlights rendered opaque: inline `background: <hex>` overrode the CSS
rgba(...,0.35). Now convert def.color via cssColorToRgb and force alpha
0.35. Added a toHaveCSS regression check in pdf-annotations.spec.ts.

Pinch-in while inline (wheel ctrlKey deltaY<0 or two-finger spread
>1.15x) now enters fullscreen. Pinch-out in fullscreen past 0.9x of
fit-scale, when already at/below fit, exits to inline and clears
userHasZoomed so refit sizes the inline view. previewScaleRaw tracks the
unclamped intent so the exit fires even when fit ~= ZOOM_MIN. A
modeTransitionInFlight latch (held 250ms post-toggle) keeps the gesture
tail from re-toggling or immediately zooming the new view.

Fullscreen toolbar: flex-wrap: nowrap and tighter 0.25rem vertical
padding (min-height 40px + safe-top instead of 48px + wrap). Search bar
top/right now follow --safe-top/--safe-right so it sits flush below the
toolbar instead of overlapping it. Base .canvas-container gets
touch-action: pan-x pan-y so the inline pinch is capturable on iOS.

* fix(pdf-server): drop --safe-top from fullscreen toolbar padding

Hosts wrap fullscreen in their own header (title + close), which already
clears the top safe-area. Adding --safe-top to our toolbar padding-top
double-dipped, leaving a visible gap between the host header and our
toolbar. Keep --safe-left/right (host header doesn't cover the sides).

* feat(pdf-server): horizontal swipe changes pages whenever page fits width

Previously gated on scale <= 1.0, which blocked page-nav in fullscreen
where fit-scale is often >100%. Now gate on actual horizontal overflow
(scrollWidth > clientWidth) so swipe works at any fit-to-width scale and
still defers to native panning once you zoom past it.

* fix(pdf-server): refit to inline width after pinch-out exits fullscreen

handleHostContextChanged calls refitScale() before the iframe has actually
shrunk, and the ResizeObserver's inline branch only refits on width
*growth* (to avoid a requestFitToContent shrink-loop). So the
fullscreen->inline shrink never triggered a refit and the page stayed at
the fullscreen scale.

Add a one-shot forceNextResizeRefit flag, set on fullscreen->inline (both
the pinch-out path and handleHostContextChanged), consumed by the
ResizeObserver on the next size change. One-shot keeps the shrink-loop
guard intact for ordinary inline resizes.

* feat(pdf-server): floor fullscreen zoom at fit-to-page

In fullscreen, pinch-out and the zoom-out button now floor at the
fit-to-page scale instead of ZOOM_MIN, so the page never shrinks below
fully-visible (no dead margin around it). previewScaleRaw stays unclamped
so a continued pinch-out past fit still triggers exit-to-inline.

* fix(pdf-server): wheel pinch-out can exit fullscreen again

The fit-floor pinned previewScale at fit, but the wheel handler multiplied
the *clamped* previewScale, so it could never accumulate below fit*0.9 to
trigger exit. Drive the wheel accumulator off previewScaleRaw instead, and
bound previewScaleRaw to [floor*0.7, ZOOM_MAX] so it can cross the 0.9
exit threshold without drifting unboundedly (which would make direction
reversal feel sticky). Touch path was unaffected (absolute ratio).

* fix(pdf-server): always refit to inline width on fullscreen exit

userHasZoomed stayed true after Escape/button/host-× exits, so refitScale()
bailed even though forceNextResizeRefit let the ResizeObserver call it.
Clear userHasZoomed in handleHostContextChanged whenever we land inline —
fullscreen zoom level is meaningless there. Dropped the now-dead
requestFitToContent fallback in the same block.

* refactor(pdf-server): rubber-band pinch-out instead of dual-tracked clamp

The previewScaleRaw side-channel made the gesture feel dead (page pinned
at fit, no feedback) and the wheel accumulator interaction was fragile.

New model: previewScale is the only tracked value. In fullscreen it may
overshoot down to 0.75*fit so the user *sees* the page pull away as they
pinch out. On commit:
  - started near fit (<=1.05*fit) AND preview <0.9*fit -> exit to inline
  - otherwise clamp committed scale to >=fit (overshoot snaps back)

beginPinch seeds fitScaleAtPinchStart synchronously from  when
!userHasZoomed (the common enter-fullscreen-at-fit case) so the first
frame already has the right floor; the async computeFitScale refines it.

* test(pdf-server): update inline-pinch e2e for new fullscreen behavior

'trackpad pinch is ignored outside fullscreen' is no longer the contract.
Replace with two tests: pinch-in inline -> .main.fullscreen appears;
pinch-out inline -> zoom unchanged, no fullscreen. The two
pdf-annotations.spec.ts failures in the previous run were flaky (passed
on retry).

Author: ochafik

examples/pdf-server/src/mcp-app.css

@@ -227,6 +227,10 @@ body {
   align-items: flex-start;
   padding: 1rem;
   background: var(--bg200);
+  /* JS owns pinch (inline pinch-in → fullscreen). pan-x/pan-y keeps native
+   * scrolling; the fullscreen rule below repeats this with a comment on the
+   * iOS-Safari preventDefault backstop. */
+  touch-action: pan-x pan-y;
 }
 
 .page-wrapper {
@@ -310,9 +314,20 @@ body {
 }
 
 .main.fullscreen .toolbar {
-  padding-top: calc(0.5rem + var(--safe-top, 0px));
-  padding-left: calc(0.5rem + var(--safe-left, 0px));
-  padding-right: calc(0.5rem + var(--safe-right, 0px));
+  /* Hosts wrap fullscreen in their own header (title + close), which already
+   * clears the top safe-area — so no --safe-top here, only sides. */
+  padding: 0.25rem calc(0.5rem + var(--safe-right, 0px)) 0.25rem
+    calc(0.5rem + var(--safe-left, 0px));
+  min-height: 40px;
+  /* Inline can wrap (narrow chat bubble); fullscreen has the width, and
+   * wrapping would double the bar height + desync the search-bar offset. */
+  flex-wrap: nowrap;
+}
+
+.main.fullscreen .search-bar {
+  /* -1px overlaps the toolbar border so the dropdown looks attached. */
+  top: 39px;
+  right: calc(var(--safe-right, 0px) - 1px);
 }
 
 .main.fullscreen .viewer {

examples/pdf-server/src/mcp-app.ts

@@ -27,6 +27,7 @@ import {
   type ImageAnnotation,
   type NoteAnnotation,
   type FreetextAnnotation,
+  cssColorToRgb,
   serializeDiff,
   deserializeDiff,
   mergeAnnotations,
@@ -341,14 +342,24 @@ async function refitScale(): Promise<void> {
 // needs height changes too (rotation, browser chrome on mobile).
 let lastContainerW = 0;
 let lastContainerH = 0;
+/** One-shot: refit on the next resize even if it's a shrink in inline mode.
+ *  Set on fullscreen→inline so the page snaps to the new (smaller) width
+ *  once the host has actually resized the iframe — the inline `grewW` gate
+ *  would otherwise swallow that shrink. */
+let forceNextResizeRefit = false;
 const containerResizeObserver = new ResizeObserver(([entry]) => {
   const { width: w, height: h } = entry.contentRect;
   const grewW = w > lastContainerW + 1;
   const changed =
     Math.abs(w - lastContainerW) > 1 || Math.abs(h - lastContainerH) > 1;
   lastContainerW = w;
   lastContainerH = h;
-  if (currentDisplayMode === "fullscreen" ? changed : grewW) refitScale();
+  if (forceNextResizeRefit && changed) {
+    forceNextResizeRefit = false;
+    refitScale();
+  } else if (currentDisplayMode === "fullscreen" ? changed : grewW) {
+    refitScale();
+  }
 });
 containerResizeObserver.observe(canvasContainerEl as HTMLElement);
 
@@ -1933,13 +1944,20 @@ function renderAnnotation(
   viewport: { width: number; height: number; scale: number },
 ): HTMLElement[] {
   switch (def.type) {
-    case "highlight":
+    case "highlight": {
+      // Force translucency: def.color is an opaque hex (e.g. "#ffff00"), which
+      // would override the rgba()/mix-blend-mode in CSS and hide the text.
+      const rgb = def.color ? cssColorToRgb(def.color) : null;
+      const bg = rgb
+        ? `rgba(${Math.round(rgb.r * 255)}, ${Math.round(rgb.g * 255)}, ${Math.round(rgb.b * 255)}, 0.35)`
+        : undefined;
       return renderRectsAnnotation(
         def.rects,
         "annotation-highlight",
         viewport,
-        def.color ? { background: def.color } : {},
+        bg ? { background: bg } : {},
       );
+    }
     case "underline":
       return renderRectsAnnotation(
         def.rects,
@@ -3322,9 +3340,13 @@ function zoomIn() {
   renderPage().then(scrollSelectionIntoView);
 }
 
-function zoomOut() {
+async function zoomOut() {
   userHasZoomed = true;
-  scale = Math.max(scale - 0.25, ZOOM_MIN);
+  // Fullscreen floor is fit-to-page (anything smaller is dead margin).
+  const fit =
+    currentDisplayMode === "fullscreen" ? await computeFitScale() : null;
+  const floor = fit !== null ? Math.max(ZOOM_MIN, fit) : ZOOM_MIN;
+  scale = Math.max(scale - 0.25, floor);
   renderPage().then(scrollSelectionIntoView);
 }
 
@@ -3761,32 +3783,77 @@ let pinchStartScale = 1.0;
 let previewScale = 1.0;
 /** Debounce timer — wheel events have no end event, so we wait for quiet. */
 let pinchSettleTimer: ReturnType<typeof setTimeout> | null = null;
+/** computeFitScale() snapshot at gesture start (async — may be null briefly). */
+let fitScaleAtPinchStart: number | null = null;
+/** Guards against firing toggleFullscreen() once per wheel event during a
+ *  single inline pinch-in gesture. */
+let modeTransitionInFlight = false;
 
 function beginPinch() {
   pinchStartScale = scale;
   previewScale = scale;
+  // Seed synchronously when we can (at fit ⇔ !userHasZoomed) so the very
+  // first updatePinch already has the right floor — avoids a one-frame
+  // jitter when the async computeFitScale resolves mid-gesture.
+  fitScaleAtPinchStart = userHasZoomed ? null : scale;
+  void computeFitScale().then((s) => (fitScaleAtPinchStart = s));
   // transform-origin matches the flex layout's anchor (justify-content:
   // center, align-items: flex-start) so the preview and the committed
   // canvas grow from the same point — otherwise the page jumps on release.
   pageWrapperEl.style.transformOrigin = "50% 0";
 }
 
+/** Fit-to-page floor for fullscreen (committed scale never goes below this).
+ *  The preview is allowed to overshoot down to 0.75×fit for rubber-band
+ *  feedback; release below 0.9×fit exits to inline, otherwise snaps to fit. */
+function pinchFitFloor(): number | null {
+  return currentDisplayMode === "fullscreen" ? fitScaleAtPinchStart : null;
+}
+
 function updatePinch(nextScale: number) {
-  previewScale = Math.min(ZOOM_MAX, Math.max(ZOOM_MIN, nextScale));
+  const fit = pinchFitFloor();
+  // Rubber-band: preview may dip to 0.75×fit so the user sees the page pull
+  // away as they pinch out. Committed scale is clamped to fit in commitPinch.
+  const previewFloor = fit !== null ? fit * 0.75 : ZOOM_MIN;
+  previewScale = Math.min(ZOOM_MAX, Math.max(previewFloor, nextScale));
   // Transform is RELATIVE to the rendered canvas (which sits at
   // pinchStartScale), so a previewScale equal to pinchStartScale → ratio 1.
   pageWrapperEl.style.transform = `scale(${previewScale / pinchStartScale})`;
   zoomLevelEl.textContent = `${Math.round(previewScale * 100)}%`;
 }
 
 function commitPinch() {
-  if (Math.abs(previewScale - scale) < 0.01) {
-    // Dead-zone — no re-render. Clear here since renderPage won't run.
+  const fit = pinchFitFloor();
+  // Pinched out past fit (page visibly pulled away) → exit fullscreen.
+  // Only when the gesture *started* near fit, so a single big pinch-out
+  // from deep zoom lands at fit instead of ejecting unexpectedly.
+  if (
+    fit !== null &&
+    pinchStartScale <= fit * 1.05 &&
+    previewScale < fit * 0.9
+  ) {
     pageWrapperEl.style.transform = "";
+    userHasZoomed = false; // let refitScale() size the inline view
+    forceNextResizeRefit = true; // ResizeObserver inline path ignores shrinks
+    modeTransitionInFlight = true;
+    void toggleFullscreen().finally(() => {
+      setTimeout(() => (modeTransitionInFlight = false), 250);
+    });
+    return;
+  }
+  // Committed scale never below fit in fullscreen — overshoot snaps back.
+  const target =
+    fit !== null
+      ? Math.max(fit, previewScale)
+      : Math.max(ZOOM_MIN, previewScale);
+  if (Math.abs(target - scale) < 0.01) {
+    // Snap-back / dead-zone — no re-render needed.
+    pageWrapperEl.style.transform = "";
+    zoomLevelEl.textContent = `${Math.round(scale * 100)}%`;
     return;
   }
   userHasZoomed = true;
-  scale = previewScale;
+  scale = target;
   // renderPage clears the transform in the same frame as the canvas
   // resize (after its first await) so there's no snap-back.
   renderPage().then(scrollSelectionIntoView);
@@ -3804,8 +3871,23 @@ canvasContainerEl.addEventListener(
     // Trackpad pinch arrives as wheel with ctrlKey set (Chrome/FF/Edge on
     // macOS+Windows, Safari on macOS). MUST check before the deltaX/deltaY
     // comparison below — pinch deltas come through on deltaY.
-    if (e.ctrlKey && currentDisplayMode === "fullscreen") {
+    if (e.ctrlKey) {
       e.preventDefault();
+      if (currentDisplayMode !== "fullscreen") {
+        // Inline: pinch-in (deltaY<0) is a request to go fullscreen.
+        // Pinch-out is ignored — nothing smaller than inline.
+        if (e.deltaY < 0 && !modeTransitionInFlight) {
+          modeTransitionInFlight = true;
+          void toggleFullscreen().finally(() => {
+            // Hold the latch through the settle window so the tail of the
+            // gesture doesn't immediately start zooming the new fullscreen
+            // view (or, worse, re-toggle).
+            setTimeout(() => (modeTransitionInFlight = false), 250);
+          });
+        }
+        return;
+      }
+      if (modeTransitionInFlight) return; // swallow gesture tail post-toggle
       if (pinchSettleTimer === null) beginPinch();
       // exp(-deltaY * k) makes equal-magnitude in/out deltas inverse —
       // pinch out then back lands where you started. Clamp per event so a
@@ -3826,10 +3908,15 @@ canvasContainerEl.addEventListener(
     // Only intercept horizontal scroll, let vertical scroll through
     if (Math.abs(e.deltaX) <= Math.abs(e.deltaY)) return;
 
-    // When zoomed, let natural panning happen (no page changes)
-    if (scale > 1.0) return;
+    // If the page overflows horizontally, let native panning handle it
+    // (no page changes). Checking actual overflow rather than `scale > 1.0`
+    // because fullscreen fit-scale is often >100% with the page still fully
+    // visible — we want swipe-to-page there. +1 absorbs sub-pixel rounding.
+    if (canvasContainerEl.scrollWidth > canvasContainerEl.clientWidth + 1) {
+      return;
+    }
 
-    // At 100% zoom, handle page navigation
+    // No horizontal overflow → swipe changes pages.
     e.preventDefault();
     horizontalScrollAccumulator += e.deltaX;
     if (horizontalScrollAccumulator > SCROLL_THRESHOLD) {
@@ -3858,7 +3945,7 @@ canvasContainerEl.addEventListener(
   "touchstart",
   (event) => {
     const e = event as TouchEvent;
-    if (e.touches.length !== 2 || currentDisplayMode !== "fullscreen") return;
+    if (e.touches.length !== 2) return;
     // No preventDefault here — keep iOS Safari happy. We block native
     // pinch-zoom via touch-action CSS + preventDefault on touchmove.
     touchStartDist = touchDist(e.touches);
@@ -3873,7 +3960,21 @@ canvasContainerEl.addEventListener(
     const e = event as TouchEvent;
     if (e.touches.length !== 2 || touchStartDist === 0) return;
     e.preventDefault(); // stop the browser zooming the whole viewport
-    updatePinch(pinchStartScale * (touchDist(e.touches) / touchStartDist));
+    const ratio = touchDist(e.touches) / touchStartDist;
+    if (currentDisplayMode !== "fullscreen") {
+      // Inline: a clear pinch-in means "go fullscreen". 1.15× threshold
+      // avoids triggering on jittery two-finger taps/scrolls.
+      if (ratio > 1.15 && !modeTransitionInFlight) {
+        modeTransitionInFlight = true;
+        touchStartDist = 0; // end this gesture; fullscreen will refit
+        pageWrapperEl.style.transform = "";
+        void toggleFullscreen().finally(() => {
+          setTimeout(() => (modeTransitionInFlight = false), 250);
+        });
+      }
+      return;
+    }
+    updatePinch(pinchStartScale * ratio);
   },
   { passive: false },
 );
@@ -3884,6 +3985,11 @@ canvasContainerEl.addEventListener("touchend", (event) => {
   // REMAINING set — lifting one of two leaves length 1.
   if (touchStartDist === 0 || e.touches.length >= 2) return;
   touchStartDist = 0;
+  if (currentDisplayMode !== "fullscreen") {
+    // Inline pinch that didn't cross the threshold — discard preview.
+    pageWrapperEl.style.transform = "";
+    return;
+  }
   commitPinch();
 });
 
@@ -4707,16 +4813,20 @@ function handleHostContextChanged(ctx: McpUiHostContext) {
     if (panelState.open) {
       setAnnotationPanelOpen(true);
     }
+    if (!isFullscreen) {
+      // Fullscreen zoom level is meaningless inline — always refit on exit,
+      // however it was triggered (pinch, button, host Escape/×).
+      userHasZoomed = false;
+      // The iframe shrink lands after this handler; let the ResizeObserver
+      // do one refit on that shrink (its inline branch normally ignores
+      // shrinks to avoid a requestFitToContent feedback loop).
+      forceNextResizeRefit = true;
+    }
     if (wasFullscreen !== isFullscreen) {
-      // Mode changed → refit. computeFitScale reads displayMode, so
-      // this scales UP to fill on enter and back DOWN to ≤1.0 on exit.
-      // refitScale → renderPage → requestFitToContent handles the
-      // host-resize on exit. If userHasZoomed, refit no-ops; on exit fall
-      // back to requestFitToContent so the iframe still shrinks to whatever
-      // scale the user left it at.
-      void refitScale().then(() => {
-        if (!isFullscreen && userHasZoomed) requestFitToContent();
-      });
+      // Fast-path refit (computeFitScale reads displayMode). The iframe may
+      // not have its final size yet — the ResizeObserver one-shot above
+      // covers the inline-shrink case once it does.
+      void refitScale();
     }
     updateFullscreenButton();
   }

tests/e2e/pdf-annotations.spec.ts

@@ -151,6 +151,12 @@ test.describe("PDF Server - Annotations", () => {
     // Check that a highlight annotation element was rendered
     const highlightEl = appFrame.locator(".annotation-highlight");
     await expect(highlightEl.first()).toBeVisible({ timeout: 5000 });
+    // Regression: highlight must be translucent (not opaque hex), so text
+    // underneath remains readable.
+    await expect(highlightEl.first()).toHaveCSS(
+      "background-color",
+      /rgba\(255, 255, 0, 0\.35\)/,
+    );
   });
 
   test("add_annotations renders multiple annotation types", async ({

tests/e2e/pdf-viewer-zoom.spec.ts

@@ -142,13 +142,13 @@ test.describe("PDF Viewer — fullscreen fit + pinch zoom", () => {
       .toBe("");
   });
 
-  test("trackpad pinch is ignored outside fullscreen", async ({ page }) => {
+  test("trackpad pinch-in while inline enters fullscreen", async ({ page }) => {
     await page.setViewportSize({ width: 1400, height: 800 });
     await loadPdfServer(page);
     await waitForPdfRender(page);
     const app = getAppFrame(page);
 
-    const before = await readZoomPercent(page);
+    await expect(app.locator(".main.fullscreen")).toHaveCount(0);
 
     await app.locator(".canvas-container").evaluate((el) => {
       el.dispatchEvent(
@@ -161,8 +161,33 @@ test.describe("PDF Viewer — fullscreen fit + pinch zoom", () => {
       );
     });
 
-    // No settle timer should have started — zoom stays put.
+    // Pinch-in should request fullscreen, not zoom the inline view.
+    await expect(app.locator(".main.fullscreen")).toHaveCount(1, {
+      timeout: 5000,
+    });
+  });
+
+  test("trackpad pinch-out while inline is a no-op", async ({ page }) => {
+    await page.setViewportSize({ width: 1400, height: 800 });
+    await loadPdfServer(page);
+    await waitForPdfRender(page);
+    const app = getAppFrame(page);
+
+    const before = await readZoomPercent(page);
+
+    await app.locator(".canvas-container").evaluate((el) => {
+      el.dispatchEvent(
+        new WheelEvent("wheel", {
+          deltaY: 50, // pinch-out
+          ctrlKey: true,
+          bubbles: true,
+          cancelable: true,
+        }),
+      );
+    });
+
     await page.waitForTimeout(300);
     expect(await readZoomPercent(page)).toBe(before);
+    await expect(app.locator(".main.fullscreen")).toHaveCount(0);
   });
 });