Add image preview for texture assets and clipboard image paste

[EmbarrassingMoment]

Summary

Adds image support to the Markdown editor without loosening the preview's Content-Security-Policy (img-src data: only — no external requests): project textures referenced with [Alt](/Game/Path/To/Texture) now render in the HTML preview, and a new Paste Image command turns a clipboard image into a texture asset with the link inserted at the cursor. Verified working in the editor with the bundled sample gauge images.

Changes

Texture references in the preview (a772206)

• New MarkdownImageUtils::EmbedTextureImages() rewrites <img> tags whose src is a UE package path (/Game/, /Engine/, /Plugins/):
  • Loads the referenced UTexture2D, compresses its source pixels to PNG via FImageUtils::CompressImage, and inlines the result as a data:image/png;base64 URI — compatible with the existing CSP, so the preview still makes no network requests
  • Unresolvable texture paths render a red dashed placeholder ([Image not found: ...], new md-missing-image CSS)
  • PNGs over 12 MB are skipped with a log warning to keep the preview data: URL bounded
  • Missing packages are pre-checked with DoesPackageExist to avoid load-failure log noise
• Hooked into UpdatePreview() after broken-link marking and heading-anchor injection

Paste Image from clipboard (a772206)

• New toolbar button / command (Ctrl+Shift+V):
  • Reads the Windows clipboard as CF_DIB, supporting 24/32 bpp, BI_RGB and BI_BITFIELDS, bottom-up and top-down row order; 32 bpp DIBs with a zeroed alpha channel (common for screenshots) are treated as opaque
  • Creates a UTexture2D asset under /Game/Markdown/Images/ with a unique timestamped name (BGRA8 source, sRGB, no mips for NPOT screenshots)
  • Inserts the matching [Name](/Game/Markdown/Images/Name) link at the cursor; the normal debounced preview refresh then embeds it
  • Editor notifications for the no-image / creation-failed / success cases; non-Windows platforms report "no image"

Tests & docs

• MarkdownImageUtilsTests (categories MarkdownAsset.Images.*): non-package src passthrough (http / data:), missing-texture placeholder output, and no-op inputs
• Editor module now depends on ImageCore
• README (en/ja): feature bullet, linking-syntax and shortcut table rows; "Image Preview" removed from Planned Features; CHANGELOG entries
• Sample gauge images under docs/sample-images/ (opaque power-of-two, alpha, and NPOT variants) used for verification (cf2b932)

How to test

1. Import the PNGs from docs/sample-images/ into the Content Browser
2. In a Markdown asset, write e.g. [HP gauge](/Game/Textures/T_GaugeBar) — the preview should show the image; a bogus path should show the red placeholder; an https:// image should stay blocked (CSP intact)
3. Copy any image to the clipboard and press Ctrl+Shift+V in the editor — a texture asset is created under /Game/Markdown/Images/ and the link is inserted
4. Automation: Tools > Session Frontend > Automation, filter MarkdownAsset, run all (includes the new MarkdownAsset.Images.* tests)

Notes

• Pasted textures are created dirty; save them normally (Save All)
• Clipboard image reading is Windows-only (the plugin currently targets Windows)

🤖 Generated with Claude Code

https://claude.ai/code/session_017MsPFParwnXFT1tjnNf27c

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Generated by Claude Code