diff --git a/engine/MUNGA_L4/L4GLASSWIN.cpp b/engine/MUNGA_L4/L4GLASSWIN.cpp
index ded2c53..744417c 100644
--- a/engine/MUNGA_L4/L4GLASSWIN.cpp
+++ b/engine/MUNGA_L4/L4GLASSWIN.cpp
@@ -1180,7 +1180,16 @@ static void
 	info.bmiHeader.biCompression = BI_RGB;
 
 	const RECT &r = w->surfaceRect;
-	SetStretchBltMode(dc, HALFTONE);
+	// STRETCH MODE (perf, 2026-08-09): default COLORONCOLOR.  HALFTONE runs a
+	// per-output-pixel resample filter; done synchronously for all 7 glass windows
+	// every ~16 Hz repaint (BTGlassPanels_Tick), it was the per-display-mode perf
+	// sink -- playtesters saw ~20 fps in the exploded panels vs ~130 fps in the
+	// cockpit surround (same scene, same machine).  The MFDs are low-res pixel
+	// content, so nearest-neighbour reads crisp (and closer to the pod CRT).
+	// BT_GLASS_SMOOTH=1 restores HALFTONE for anyone who prefers smoothing to speed.
+	static int sSmooth = -1;
+	if (sSmooth < 0) sSmooth = getenv("BT_GLASS_SMOOTH") ? 1 : 0;
+	SetStretchBltMode(dc, sSmooth ? HALFTONE : COLORONCOLOR);
 	SetBrushOrgEx(dc, 0, 0, NULL);
 	StretchDIBits(dc,
 		r.left, r.top, r.right - r.left, r.bottom - r.top,