From ba646fb233d01ef871ed9309af56d8c33008ed2c Mon Sep 17 00:00:00 2001
From: Greg Pomerantz <gmp@wow.st>
Date: Tue, 3 Nov 2026 13:15:55 -0500
Subject: [PATCH] gtauri viewer: adopt incoming dimensions at swipe commit
 (aspect fix)
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Settling on a different-aspect neighbor (e.g. landscape → portrait)
stretched: vimg kept the OLD image's width/height styles while showing
the new thumbnail, so the new pixels rendered in the old box until
full-res landed and fitViewer() reset the dimensions — a visible
vertical stretch then snap-back.

At the commit swap, adopt the incoming image's dimensions from the
drag preview (nav already knows w/h/scale from its loaded thumb):
base/vScale/width/height/transform are all set consistently in the
same task as the src swap, so the first settled frame is correct.
Fallback: if the preview never loaded (keyboard nav / slow thumb),
use the plain openViewer path where the thumb round-trip sets the
dimensions before first paint.

Verified on the emulator with a 4:3 landscape + 3:4 portrait pair:
settled content box 1439x1921 (0.749 = exact 3:4) from the first
settled frame, unchanged after the full-res swap.
---
 harnesses/gtauri/frontend/dist/index.html | 28 +++++++++++++++++------
 1 file changed, 21 insertions(+), 7 deletions(-)

diff --git a/harnesses/gtauri/frontend/dist/index.html b/harnesses/gtauri/frontend/dist/index.html
index a6e97bd..eccc433 100644
--- a/harnesses/gtauri/frontend/dist/index.html
+++ b/harnesses/gtauri/frontend/dist/index.html
@@ -573,15 +573,29 @@ function commitTo(ni, delta) {
     if (t < 1) {
       tween = { raf: requestAnimationFrame(step), commit: true };
     } else {
-      // vimg2 (incoming) is exactly at 0: it becomes primary.
       const id = ids[ni];
-      vimg.src = vimg2.src; // cached + decoded → paints immediately
-      vTx = 0;
-      applyTransform();
       tween = null;
-      openViewer(id, true);
-      // Hide the outgoing preview only once the primary has the bytes.
-      vimg.onload = () => { if (viewerId === id) navHide(); };
+      if (nav && nav.id === id && nav.ready) {
+        // vimg2 (incoming) is exactly at 0: it becomes primary. Adopt
+        // its dimensions NOW — otherwise the new pixels render in the
+        // OLD image's width/height box (wrong aspect) until full-res
+        // lands and fitViewer() fixes it (visible stretch → snap).
+        const nw = nav.w, nh = nav.h, ns = nav.scale;
+        vimg.src = vimg2.src; // cached + decoded → paints immediately
+        base.w = nw; base.h = nh;
+        vScale = ns;
+        vimg.style.width = nw + "px";
+        vimg.style.height = nh + "px";
+        vTx = 0; vTy = 0;
+        applyTransform();
+        openViewer(id, true);
+        // Hide the preview only once the primary has the bytes.
+        vimg.onload = () => { if (viewerId === id) navHide(); };
+      } else {
+        // Preview never made it (keyboard nav / slow thumb): plain
+        // open — the thumb round-trip sets the right dimensions.
+        openViewer(id, false);
+      }
     }
   };
   tween = { raf: requestAnimationFrame(step), commit: true };