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AI OSD: Screen Overlay

AI-first map of Blazor screen overlay and OSD canvas APIs.

Screen Overlay / Blazor OSD Discovery Map

Reference map for drawing screen annotations through the Blazor-backed overlay canvas: rectangles, HTML labels, Razor components, and CV debug boxes.

Interactive picking belongs to osd/selection.md.

User Intents

  • Draw a rectangle around a region.
  • Show HTML label or badge over the desktop.
  • Render a Razor component as a floating annotation.
  • Display CV/ML bounding boxes.
  • Open overlay WebView DevTools.

Concept Model

  • IOnScreenService creates owner-scoped canvases.
  • IOnScreenCanvasScriptingApi is the script-facing canvas factory.
  • IOnScreenCanvas owns IOnScreenObject instances by OnScreenObjectId.
  • Canvas visibility is owner-scoped: hiding one canvas temporarily removes its objects from rendering without affecting other canvases or discarding the hidden owner's objects.
  • Objects use desktop screen coordinates.
  • Current rendered object contracts are IOnScreenRectangle, IOnScreenHtml, and IOnScreenRazor.
  • The renderer uses a transparent click-through Blazor/WebView window internally; consumers should use canvas/object APIs.

API Details

  • IOnScreenService - runtime canvas factory and DevTools hook.
  • IOnScreenCanvasScriptingApi - script-facing canvas factory.
  • IOnScreenCanvas - ObjectsById, IsVisible, AddOrUpdate, Remove, Clear, ShowDevTools.
  • IOnScreenObject - Id, Location, Size, Opacity, IsVisible.
  • IOnScreenRectangle - Background, BorderColor, BorderThickness.
  • IOnScreenHtml - raw trusted Html.
  • IOnScreenRazor - ViewType and DataContext.
  • OnScreenCanvasExtensions - AddRectangle, AddHtmlObject, AddRazor<T>.

Prefer

  • Prefer IOnScreenCanvasScriptingApi for script-owned overlays.
  • Prefer IOnScreenService for app/runtime code.
  • Prefer AddRectangle, AddHtmlObject, and AddRazor<T> for built-in objects.
  • Prefer disposing objects/canvas for cleanup.
  • Prefer windows-subsystems/blazor-windows.md for real windows.
  • Prefer nuget/imgui-sdk.md for ImGui UI.

Avoid

  • Avoid creating custom transparent WebView windows for simple annotations.
  • Avoid untrusted HTML in IOnScreenHtml.
  • Avoid using screen overlay as an input picker.

Research Anchors

  • IOnScreenCanvas, IOnScreenCanvasScriptingApi, IOnScreenService, IOnScreenObject, IOnScreenRectangle, IOnScreenHtml, IOnScreenRazor, OnScreenCanvasExtensions, AddRectangle, AddHtmlObject, AddRazor, OnScreenOverlayComponent.

Search Synonyms

  • screen overlay
  • Blazor OSD
  • desktop overlay
  • click-through overlay
  • bounding box overlay
  • debug overlay
  • HTML overlay
  • Razor overlay
  • screen annotation
  • osd/selection.md
  • windows-subsystems/blazor-windows.md
  • nuget/imgui-sdk.md
  • computer-vision/images.md