From 4326d3f029bd904aab66a20020e4e70150011e6e Mon Sep 17 00:00:00 2001
From: Vlad Zahorodnii <vlad.zahorodnii@kde.org>
Date: Sat, 19 Feb 2022 18:38:05 +0200
Subject: [PATCH] effects/blur: Avoid shrinking unrelated opaque regions

Currently, the blur effect will shrink an opaque region even if it
doesn't intersect m_currentBlur.

This ensures that the blur effect won't do a stupid thing such as
clipping the opaque region of the desktop window.
---
 src/effects/blur/blur.cpp | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/src/effects/blur/blur.cpp b/src/effects/blur/blur.cpp
index a451c15ea3..763f0c2bdb 100644
--- a/src/effects/blur/blur.cpp
+++ b/src/effects/blur/blur.cpp
@@ -542,20 +542,22 @@ void BlurEffect::prePaintWindow(EffectWindow* w, WindowPrePaintData& data, std::
         return;
     }
 
-    // to blur an area partially we have to shrink the opaque area of a window
-    QRegion newClip;
-    const QRegion oldClip = data.clip;
-    for (const QRect &rect : data.clip) {
-        newClip |= rect.adjusted(m_expandSize, m_expandSize, -m_expandSize, -m_expandSize);
-    }
-    data.clip = newClip;
+    if (data.clip.intersects(m_currentBlur)) {
+        // to blur an area partially we have to shrink the opaque area of a window
+        QRegion newClip;
+        const QRegion oldClip = data.clip;
+        for (const QRect &rect : data.clip) {
+            newClip |= rect.adjusted(m_expandSize, m_expandSize, -m_expandSize, -m_expandSize);
+        }
+        data.clip = newClip;
 
-    // we don't have to blur a region we don't see
-    m_currentBlur -= newClip;
-    // if we have to paint a non-opaque part of this window that intersects with the
-    // currently blurred region we have to redraw the whole region
-    if ((data.paint - oldClip).intersects(m_currentBlur)) {
-        data.paint |= m_currentBlur;
+        // we don't have to blur a region we don't see
+        m_currentBlur -= newClip;
+        // if we have to paint a non-opaque part of this window that intersects with the
+        // currently blurred region we have to redraw the whole region
+        if ((data.paint - oldClip).intersects(m_currentBlur)) {
+            data.paint |= m_currentBlur;
+        }
     }
 
     // in case this window has regions to be blurred