[graphics/krita] libs/ui/tool: Fix preview size on canvas jumping around because of rounding errors

Git commit 749a248f16b75b1e58a2041f24dc92549752bd99 by Emmet O'Neill, on behalf of Dat Le.
Committed on 13/08/2026 at 23:16.
Pushed by emmetoneill into branch 'master'.

Fix preview size on canvas jumping around because of rounding errors

M  +6    -2    libs/ui/tool/KisAsyncColorSamplerHelper.cpp

https://invent.kde.org/graphics/krita/-/commit/749a248f16b75b1e58a2041f24dc92549752bd99

diff --git a/libs/ui/tool/KisAsyncColorSamplerHelper.cpp b/libs/ui/tool/KisAsyncColorSamplerHelper.cpp
index aac74fbc075..95501e80e58 100644
--- a/libs/ui/tool/KisAsyncColorSamplerHelper.cpp
+++ b/libs/ui/tool/KisAsyncColorSamplerHelper.cpp
@@ -741,10 +741,14 @@ QImage KisAsyncColorSamplerHelper::cacheCanvasImage(QRect &canvasPixelRect) {
 void KisAsyncColorSamplerHelper::paintCircleCanvasPreview(QPainter &gc, const QRectF &viewRectF, const QRectF &zoomDocRectF, const QPainterPath &clip) {
     KisImageWSP image = m_d->canvas->image();
 
-    QRect canvasPixelRect = image->documentToPixel(zoomDocRectF).toRect();
+    QRectF canvasPixelRectF = image->documentToPixel(zoomDocRectF);
+
+    // Floor manually to avoid width != height when using toRect()
+    QRect canvasPixelRect = QRect(canvasPixelRectF.topLeft().toPoint(), QSize(qFloor(canvasPixelRectF.width()), qFloor(canvasPixelRectF.height())));
+
     canvasPixelRect = m_d->standardizeZoomPreviewPixelRect(canvasPixelRect);
 
-    // Make sure the center is the pixel currently sampled (in case of rounding errors)
+    // Make sure the center is the pixel currently sampled because standardizing may change the shape
     canvasPixelRect.moveCenter(image->documentToImagePixelFloored(zoomDocRectF.center()));
 
     QImage cachedImage = cacheCanvasImage(canvasPixelRect);