[minor] Add PixelLoupe, a magnified pixel readout beside an ImageCanvas - #574
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ImGuiWidgets.PixelLoupe draws a grid of the pixels around the pointer while it is over an ImageCanvas, outlines the centre pixel, and reads it out as coordinates, RGBA and hex. It also marks that pixel on the canvas. Pixels come from a caller-supplied callback, so no texture is read back, and the loupe takes no input, so the canvas keeps its pan and zoom. PixelLoupeState holds the hover and clamping rules with no ImGui dependency. ImageCanvasState gains ImageToViewport, the inverse of ViewportToImage. The gallery's SampleImage exposes PixelAt so the loupe tile reads the same pixels the texture holds. Closes #529 Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01LXUsRiHnKs6HCgLAbC1L6D
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01HgjMCJ9MQRmUk6c8KABDYH
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This was referenced Oct 1, 2026
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Requested by Matt · project thread
Before: an
ImageCanvasgave no way to inspect the exact value of the pixel under the pointer.After: while the pointer is over an
ImageCanvas,ImGuiWidgets.PixelLoupedraws a magnified grid of the surrounding pixels. It outlines the centre pixel, marks the same pixel on the canvas, and reads it out as coordinates, RGBA and hex. Pixels come from a callback the caller supplies, so nothing is read back from the GPU. The loupe takes no input, so the canvas keeps its own pan and zoom.How:
PixelLoupeStateholds the hover and clamping rules and has no ImGui dependency.ImageCanvasState.ImageToViewportis the same inverse mapping the CropOverlay PR adds, so it appears only once in the stack. The gallery'sSampleImageexposesPixelAt, so the loupe tile reads the same pixels the texture holds. The PR adds a demo section, an isolation suite, a gallery tile and docs entries.Stacked PR. The base is #573 (CropOverlay), and this is the top of the image-widget stack. Merge order: #570 → #571 → #572 → #573 → this.
Validation, Release build: the solution builds clean, and
ImGuiWidgetsDemo.UITestspasses 46/46. On this top branch,ImGui.Widgets.Testspasses 931/931,ImGui.Widgets.UITests629/629 andWidgetGallery.UITests6/6, andWidgetGallery --checkpasses.Closes #529
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https://claude.ai/code/session_01LXUsRiHnKs6HCgLAbC1L6D
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