Add Edge Overflow Indicators

Windows OS version

Windows 11 25H2

ImageGlass version

10.0.3.720-rc-win-x64

ImageGlass release

Classic

1️⃣ Describe the feature

Show Edge Overflow Indicators" feature is very useful.

Add Edge Overflow Indicators — thin colored lines along the window borders that show which directions the image extends beyond the current viewport.

When an image is zoomed in and panned so that parts of it lie outside the visible window area, a subtle indicator line appears on the corresponding edge(s) (top, bottom, left, right).

This gives users instant visual feedback about where the image continues without having to guess or pan blindly.

Settings should include:

1. Off — disable indicators.
2. On — enable with a default accent color.
3. Custom — let users pick their own indicator color (e.g., green, red, or any hex color).

The indicator lines should be thin (1–2 px), non-intrusive, and fade out when the edge is fully within the viewport.

2️⃣ How to use feature

1. Open any image in ImageGlass.
2. Zoom in (e.g., 200%+) and pan the image so that a portion goes off-screen.
3. Notice the thin colored line appearing on the window edge(s) where the image overflows — e.g., a green line on the left edge means there is more image content to the right.
4. Pan toward that direction to reveal the hidden portion; the indicator disappears once the edge is reached.
5. Customize the indicator color in Settings → Image (or a new View tab): choose Off, On (default color), or Custom (color picker).

3️⃣ Additional context

This feature is extremely helpful when inspecting large images (maps, blueprints, high-res scans, comics) at high zoom levels, as it eliminates the "am I at the edge?" guesswork.

A good reference is QuickView's implementation, where the setting is named "Show Edge Overflow Indicators" with the description: "Shows an indicator line in the direction where the image exceeds the window borders." It offers Off / On / Custom color modes.

I hope it's okay to reference another project here — no disrespect to ImageGlass intended; I only want to provide a concrete example of the feature I'm describing.

The indicator should ideally support high-DPI displays and adapt to the current theme (light/dark) if set to "On".

Start by locating the image viewport and pan behavior, then inspect the Settings → Image area where the Off, On, and Custom modes would be added. Compare the existing UI and rendering structure with the requested high-DPI and light/dark behavior; done means overflow indicators appear on the correct edges, disappear at the image boundary, and can be configured as described.