Server sends COMMAND_SCREEN_PREVIEW_REQ when user double-clicks an
active (non-Locked/Inactive) host that advertises CLIENT_CAP_SCREEN_PREVIEW.
Client BitBlts primary screen, encodes to JPEG via GDI+ and replies. The
existing STATIC tooltip is replaced with a self-drawn CPreviewTipWnd
showing the thumbnail above the host info text, with wide-character
rendering so the popup also works on non-Chinese servers.
- Quality tiers reuse QualityProfile pattern: PreviewProfile + 6 levels
driven by GetTargetQualityLevel (FRP-aware), with 4K/ultrawide auto
upscale on Ultra/High tiers up to min(screenWidth/4, 1280).
- Client limits to 1 in-flight capture via atomic counter to defend
against flood/DoS; Send2Server is already mutex-serialized.
- Server validates responses by reqId only (single in-flight tip);
4s arrival timeout marks "preview unavailable" without blocking the
text fallback path.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
