From 36440a9d91915a8885a8bbcc1b2dcf39428f07ed Mon Sep 17 00:00:00 2001
From: David Edmundson <kde@davidedmundson.co.uk>
Date: Wed, 12 Oct 2022 11:28:25 +0000
Subject: [PATCH] Fix scripted shader effect animations

AnimationEffect inherits from CrossfadeEffect as it may do a crossfade,
but it also has to perform non-crossfading activities with a custom
shader.

For crossfades we want to draw the old and new window, but this isn't
needed where the crossFadeProgress remains at 0.

BUG: 460277
---
 src/libkwineffects/kwineffects.cpp         |  2 +-
 src/libkwineffects/kwinoffscreeneffect.cpp | 15 ++++++++++-----
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/src/libkwineffects/kwineffects.cpp b/src/libkwineffects/kwineffects.cpp
index 56299aea9a..825e127afb 100644
--- a/src/libkwineffects/kwineffects.cpp
+++ b/src/libkwineffects/kwineffects.cpp
@@ -251,7 +251,7 @@ WindowPaintData::WindowPaintData(const QMatrix4x4 &screenProjectionMatrix)
     setSaturation(1.0);
     setBrightness(1.0);
     setScreen(0);
-    setCrossFadeProgress(1.0);
+    setCrossFadeProgress(0.0);
 }
 
 WindowPaintData::WindowPaintData(const WindowPaintData &other)
diff --git a/src/libkwineffects/kwinoffscreeneffect.cpp b/src/libkwineffects/kwinoffscreeneffect.cpp
index 6ee3092dc0..5353f73d18 100644
--- a/src/libkwineffects/kwinoffscreeneffect.cpp
+++ b/src/libkwineffects/kwinoffscreeneffect.cpp
@@ -280,16 +280,21 @@ void CrossFadeEffect::drawWindow(EffectWindow *window, int mask, const QRegion &
 {
     Q_UNUSED(mask)
 
+    CrossFadeWindowData *offscreenData = d->windows.value(window);
+
     // paint the new window (if applicable) underneath
-    Effect::drawWindow(window, mask, region, data);
+    if (data.crossFadeProgress() > 0 || !offscreenData) {
+        Effect::drawWindow(window, mask, region, data);
+    }
+
+    if (!offscreenData) {
+        return;
+    }
 
     // paint old snapshot on top
     WindowPaintData previousWindowData = data;
     previousWindowData.setOpacity((1.0 - data.crossFadeProgress()) * data.opacity());
-    CrossFadeWindowData *offscreenData = d->windows[window];
-    if (!offscreenData) {
-        return;
-    }
+
     const QRectF expandedGeometry = window->expandedGeometry();
     const QRectF frameGeometry = window->frameGeometry();