wallpaper: keep the burn's cover clear until both pictures are decoded

A brief flicker was left at the start of the burn on both screens. The
cover drew each picture as soon as it decoded, and the new one, under
the old, usually decodes first, so it showed for a frame or two before
the old one covered it. Both now stay hidden until both are ready; the
surface is clear until then, and swaybg underneath is still showing
the old picture, since wallp waits for covered().

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/desktop/modules/appearance/WallpaperSpread.qml b/desktop/modules/appearance/WallpaperSpread.qml
index 2f1dd03..02e5f94 100644
--- a/desktop/modules/appearance/WallpaperSpread.qml
+++ b/desktop/modules/appearance/WallpaperSpread.qml
@@ -86,8 +86,13 @@ Scope {
             }
 
             // -m fill is a centred crop, which is what PreserveAspectCrop does.
+            // Both hidden until both are decoded: the new one usually lands
+            // first, and drawn under an old one still loading it flashed
+            // the new picture before the burn. Until then the surface is
+            // clear and swaybg shows the old picture itself.
             Image {
                 id: newImg
+                visible: win.ready
                 anchors.fill: parent
                 fillMode: Image.PreserveAspectCrop
                 sourceSize: Qt.size(win.width, win.height)
@@ -97,6 +102,7 @@ Scope {
 
             Image {
                 id: oldImg
+                visible: win.ready
                 anchors.fill: parent
                 fillMode: Image.PreserveAspectCrop
                 sourceSize: Qt.size(win.width, win.height)