[graphics/krita] libs/ui: Improve reference image color sampling accuracy

Git commit 50d84c8bd600acb35b7561cc436d0bd5dd980cd1 by Emmet O'Neill, on behalf of Dat Le.
Committed on 13/08/2026 at 23:16.
Pushed by emmetoneill into branch 'master'.

Improve reference image color sampling accuracy

By removing unnecessary conversion inside KisReferernceImagesLayer::getPixel to avoid some fractions of errors

M  +3    -4    libs/ui/flake/KisReferenceImagesLayer.cpp
M  +1    -1    libs/ui/flake/KisReferenceImagesLayer.h
M  +1    -3    libs/ui/tool/KisAsyncColorSamplerHelper.cpp
M  +3    -1    libs/ui/widgets/KisScreenColorSampler.cpp

https://invent.kde.org/graphics/krita/-/commit/50d84c8bd600acb35b7561cc436d0bd5dd980cd1

diff --git a/libs/ui/flake/KisReferenceImagesLayer.cpp b/libs/ui/flake/KisReferenceImagesLayer.cpp
index 4386fd71f54..dd8a0e0b638 100644
--- a/libs/ui/flake/KisReferenceImagesLayer.cpp
+++ b/libs/ui/flake/KisReferenceImagesLayer.cpp
@@ -251,19 +251,18 @@ QRectF KisReferenceImagesLayer::boundingImageRect() const
     return converter()->documentToView(boundingRect());
 }
 
-KoColor KisReferenceImagesLayer::getPixel(QPointF position) const
+KoColor KisReferenceImagesLayer::getPixel(QPointF docPosition) const
 {
     KoColor transparent;
     transparent.setOpacity(0.0);
-    const QPointF docPoint = converter()->viewToDocument(position);
 
-    KoShape *shape = shapeManager()->shapeAt(docPoint);
+    KoShape *shape = shapeManager()->shapeAt(docPosition);
 
     if (shape) {
         auto *reference = dynamic_cast<KisReferenceImage*>(shape);
         KIS_SAFE_ASSERT_RECOVER_RETURN_VALUE(reference, transparent);
 
-        return reference->getPixel(docPoint);
+        return reference->getPixel(docPosition);
     }
 
     return transparent;
diff --git a/libs/ui/flake/KisReferenceImagesLayer.h b/libs/ui/flake/KisReferenceImagesLayer.h
index 4dc2e747a5d..3c65f6ccd99 100644
--- a/libs/ui/flake/KisReferenceImagesLayer.h
+++ b/libs/ui/flake/KisReferenceImagesLayer.h
@@ -27,7 +27,7 @@ public:
     QVector<KisReferenceImage*> referenceImages() const;
 
     QRectF boundingImageRect() const;
-    KoColor getPixel(QPointF position) const;
+    KoColor getPixel(QPointF docPosition) const;
 
     void paintReferences(QPainter &painter);
 
diff --git a/libs/ui/tool/KisAsyncColorSamplerHelper.cpp b/libs/ui/tool/KisAsyncColorSamplerHelper.cpp
index 63386560ea5..0d89528f1e6 100644
--- a/libs/ui/tool/KisAsyncColorSamplerHelper.cpp
+++ b/libs/ui/tool/KisAsyncColorSamplerHelper.cpp
@@ -778,14 +778,12 @@ void KisAsyncColorSamplerHelper::slotAddSamplingJob(const QPointF &docPoint)
     if (!m_d->strokeId) return;
 
     KisImageSP image = m_d->canvas->image();
-
-    dbgUI << "Original doc point in slotAddSamplingJob:" << docPoint;
     const QPoint imagePoint = image->documentToImagePixelFloored(docPoint);
 
     if (!m_d->sampleCurrentLayer) {
         KisSharedPtr<KisReferenceImagesLayer> referencesLayer = m_d->canvas->imageView()->document()->referenceImagesLayer();
         if (referencesLayer && m_d->canvas->referenceImagesDecoration()->visible()) {
-            KoColor color = referencesLayer->getPixel(imagePoint);
+            KoColor color = referencesLayer->getPixel(docPoint);
             if (color.opacityU8() > 0) {
                 slotColorSamplingFinished(color);
                 return;
diff --git a/libs/ui/widgets/KisScreenColorSampler.cpp b/libs/ui/widgets/KisScreenColorSampler.cpp
index d2cdcaa7ec9..fdeac54291e 100644
--- a/libs/ui/widgets/KisScreenColorSampler.cpp
+++ b/libs/ui/widgets/KisScreenColorSampler.cpp
@@ -171,11 +171,13 @@ KoColor KisScreenColorSampler::grabScreenColor(const QPoint &p)
 
                 if (image) {
                     QPointF imagePoint = canvas->coordinatesConverter()->widgetToImage(widgetPoint);
+                    // KisReferenceImagesLayer::getPixel use document coordinate
+                    QPointF docPoint = canvas->coordinatesConverter()->widgetToDocument(widgetPoint);
                     // sample from reference images first
                     KisSharedPtr<KisReferenceImagesLayer> referenceImageLayer = view->document()->referenceImagesLayer();
 
                     if (referenceImageLayer && canvas->referenceImagesDecoration()->visible()) {
-                        KoColor color = referenceImageLayer->getPixel(imagePoint);
+                        KoColor color = referenceImageLayer->getPixel(docPoint);
                         if (color.opacityU8() > 0) {
                             return color.convertedTo(image->colorSpace());
                         }