From b580fdafad61c3f797c707409268eb1db76c3038 Mon Sep 17 00:00:00 2001
From: vicrodh <103399283+vicrodh@users.noreply.github.com>
Date: Tue, 28 Jul 2026 16:22:19 -0600
Subject: [PATCH] fix(qbz-qt): rasterize every Canvas on the GUI thread
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The owner hit a segfault after clicking around. Cooperative and Threaded
rasterize on the scene-graph RENDER thread, and RoundedImage is instantiated in
25 files — every card, row and queue row — so list recycling creates and
destroys hundreds of these while async artwork callbacks schedule repaints on
them. The render thread can be mid-draw on a pixmap whose Canvas is already
gone. The ambient field makes it worse by repainting 30 times a second for the
whole window lifetime on that same thread.

Immediate keeps paint and destruction on one thread. renderTarget: Image
already meant CPU raster, so nothing looks different.

Not yet confirmed on hardware: the decisive check is running the previous
binary with QSG_RENDER_LOOP=basic, which gives Cooperative no separate thread
to race with. If that survives the repro and the default loop does not, this is
the cause.

cc
---
 crates/qbz-qt/qml/cards/PlaylistCollage.qml | 5 ++++-
 crates/qbz-qt/qml/shell/AmbientField.qml    | 5 ++++-
 crates/qbz-qt/qml/theme/RoundedImage.qml    | 8 +++++++-
 3 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/crates/qbz-qt/qml/cards/PlaylistCollage.qml b/crates/qbz-qt/qml/cards/PlaylistCollage.qml
index cb1436b69..f198028fe 100644
--- a/crates/qbz-qt/qml/cards/PlaylistCollage.qml
+++ b/crates/qbz-qt/qml/cards/PlaylistCollage.qml
@@ -135,7 +135,10 @@ Item {
         id: canvas
         anchors.fill: parent
         renderTarget: Canvas.Image
-        renderStrategy: Canvas.Cooperative
+        // See RoundedImage.qml: GUI-thread raster. This canvas repaints from
+        // libraryArtworkReady and from four async image probes, on a card the
+        // feed recycles.
+        renderStrategy: Canvas.Immediate
 
         // Dimension probes: Canvas cannot query a loaded image's intrinsic
         // size and the crop fit needs it (RoundedImage's pattern, one per
diff --git a/crates/qbz-qt/qml/shell/AmbientField.qml b/crates/qbz-qt/qml/shell/AmbientField.qml
index 5dff24c58..7391fbdc6 100644
--- a/crates/qbz-qt/qml/shell/AmbientField.qml
+++ b/crates/qbz-qt/qml/shell/AmbientField.qml
@@ -45,7 +45,10 @@ Canvas {
         : true
 
     renderTarget: Canvas.Image
-    renderStrategy: Canvas.Cooperative
+    // See RoundedImage.qml. This one repaints 30x/s for the whole window
+    // lifetime, so it is the canvas most likely to be mid-raster when another
+    // is torn down on the same render thread.
+    renderStrategy: Canvas.Immediate
 
     // The shader clock (t = time * 0.75). Accumulated at ~30fps.
     property real t: Math.random() * 40.0
diff --git a/crates/qbz-qt/qml/theme/RoundedImage.qml b/crates/qbz-qt/qml/theme/RoundedImage.qml
index 429905ff4..bccc26eea 100644
--- a/crates/qbz-qt/qml/theme/RoundedImage.qml
+++ b/crates/qbz-qt/qml/theme/RoundedImage.qml
@@ -25,7 +25,13 @@ Canvas {
     property string fit: "crop"
 
     renderTarget: Canvas.Image
-    renderStrategy: Canvas.Cooperative
+    // GUI-thread raster. Cooperative/Threaded rasterize on the SCENE GRAPH
+    // RENDER THREAD, and this item is created and destroyed by list recycling
+    // while async artwork callbacks schedule repaints — the render thread can
+    // be mid-draw on a pixmap whose Canvas is already gone. Immediate keeps
+    // paint and destruction on one thread. renderTarget: Image already meant
+    // CPU raster, so this costs no visual change.
+    renderStrategy: Canvas.Immediate
 
     // Dimension probe: Canvas can't query the loaded image's intrinsic
     // size, and PreserveAspectCrop needs it. A hidden Image doubles as