NW.js Guest Webview Margin Compatibility & Universal Canvas Centering

The Open Publisher desktop client wraps the core web application inside a native NW.js shell, hosting the editor within a container webview. To provide a professional desktop feel, the desktop wrapper injects wide horizontal pasteboard margins around the paper canvas, allowing expansive scratch workspace. However, differences between browser Flexbox auto-centering and desktop container margins previously caused subtle navigation bugs: clicking the floating "Return to Page" button could strand the document at the far right of the screen, or scrolling into the pasteboard could trigger coordinate conflicts. Version 5.7.8 engineered deep margin awareness and universal visual centering across both Single-Page and Multi-Page modes.

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[Screenshot: NW.js Guest Desktop Canvas with Balanced Pasteboard Margins (700 x 360)]

The active document lands squarely in the visual center of the desktop window when returning from scratch space or switching view modes.

NW.js Pasteboard Margin Architecture & Defect Resolution

Inside the desktop application, wrapper.html injects wide horizontal margins (typically 765px to 960px) into #paper while setting the viewport to justify-content: flex-start:

Right-Offset Defect Fix: Previously, returnToPage() hardcoded horizontal scrolling to 0. In the NW.js client, scrolling to scrollLeft = 0 parked the viewport at the far-left margin, leaving the document stranded far over to the right. Version 5.7.8 calculates the true visual center (paperVisualCenter = paper.offsetLeft + paper.offsetWidth / 2) and scrolls the viewport to position the page symmetrically.
Top-Left Jump Elimination: In earlier builds, scrolling down and right into scratch space caused updateCanvasScrollBounds() to assign conflicting inline paper.style.left offsets on top of desktop margins, triggering coordinate resets. Version 5.7.8 introduced hasCustomMargin detection, skipping inline style left assignments and computing effective bounds as paper.offsetLeft + scaledW + marginRight.
Exact Top Padding Rest Position: Vertical return positioning targets paperVisualTop - 50px, providing an exact 50px top padding resting spot aligned with the vertical ruler origin.

Universal Multi-Page Mode Return & Flexbox Alignment

Multi-Page Overview mode received full architectural alignment to prevent coordinate overflow:

Flexbox Alignment Protection: Added !important to .viewport.multi-page-mode flex rules (justify-content: flex-start !important; align-items: flex-start !important;). This prevents Flexbox from centering oversized overview grids into negative coordinates.
Targeted Slot Centering: When viewing the document in Multi-Page Overview, clicking "Return to Page" automatically centers the currently active page slot (slots[state.currentPageIndex]) and resets vertical scrolling to 0.
Adaptive Fit Commands: Enhanced fitToPage() and fitToWidth() to compute horizontal centering based on paperVisualCenter whenever desktop wrapper margins are active.

Automated Test Verification

Four comprehensive automated test suites validated NW.js guest frame simulations and standard web browsers in Chromium and Firefox, confirming 0px horizontal center offsets, clean scroll resets, and reliable floating button behavior across all navigation scenarios.

Tip: You can press the Home key or click the floating return button at any time to instantly center your document on screen.