From eb27d312a3fde22976b8a020dcd20cd53b723e2b Mon Sep 17 00:00:00 2001
From: Vlad Zahorodnii <vlad.zahorodnii@kde.org>
Date: Thu, 27 May 2021 18:52:10 +0300
Subject: [PATCH] effects/desktopgrid: Clip windows differently

Similar to the slide effect, the desktop grid can use the clip region to
clip windows when needed. This will improve performance because the desktop
grid effect will do less work. Currently, it clips quads on its own in
prePaintWindow, copies them over in a temporary list, and lets the opengl
scene clip the window quads again.

We can clip windows differently by just passing a custom region to the
paintWindow() function down the effects chain, which the desktop grid
effect already does.

The old behavior and the old bugs are preserved. The Xrender code path is
unaffected.
---
 src/effects/desktopgrid/desktopgrid.cpp | 41 +++++--------------------
 1 file changed, 7 insertions(+), 34 deletions(-)

diff --git a/src/effects/desktopgrid/desktopgrid.cpp b/src/effects/desktopgrid/desktopgrid.cpp
index 7de79aac05..cd4f2d2e50 100644
--- a/src/effects/desktopgrid/desktopgrid.cpp
+++ b/src/effects/desktopgrid/desktopgrid.cpp
@@ -291,18 +291,6 @@ void DesktopGridEffect::prePaintWindow(EffectWindow* w, WindowPrePaintData& data
                 w->enablePainting(EffectWindow::PAINT_DISABLED_BY_MINIMIZE);
             data.mask |= PAINT_WINDOW_TRANSFORMED;
 
-            // Split windows at screen edges
-            for (int screen = 0; screen < effects->numScreens(); screen++) {
-                QRect screenGeom = effects->clientArea(ScreenArea, screen, 0);
-                if (w->x() < screenGeom.x())
-                    data.quads = data.quads.splitAtX(screenGeom.x() - w->x());
-                if (w->x() + w->width() > screenGeom.x() + screenGeom.width())
-                    data.quads = data.quads.splitAtX(screenGeom.x() + screenGeom.width() - w->x());
-                if (w->y() < screenGeom.y())
-                    data.quads = data.quads.splitAtY(screenGeom.y() - w->y());
-                if (w->y() + w->height() > screenGeom.y() + screenGeom.height())
-                    data.quads = data.quads.splitAtY(screenGeom.y() + screenGeom.height() - w->y());
-            }
             if (windowMove && wasWindowMove && windowMove->findModal() == w)
                 w->disablePainting(EffectWindow::PAINT_DISABLED_BY_DESKTOP);
         } else
@@ -329,37 +317,22 @@ void DesktopGridEffect::paintWindow(EffectWindow* w, int mask, QRegion region, W
             QRect screenGeom = effects->clientArea(ScreenArea, screen, 0);
 
             QRectF transformedGeo = w->frameGeometry();
-            // Display all quads on the same screen on the same pass
-            WindowQuadList screenQuads;
-            bool quadsAdded = false;
             if (isUsingPresentWindows()) {
                 WindowMotionManager& manager = m_managers[(paintingDesktop-1)*(effects->numScreens())+screen ];
                 if (manager.isManaging(w)) {
-                    foreach (const WindowQuad & quad, data.quads)
-                        screenQuads.append(quad);
                     transformedGeo = manager.transformedGeometry(w);
-                    quadsAdded = true;
                     if (!manager.areWindowsMoving() && timeline.currentValue() == 1.0)
                         mask |= PAINT_WINDOW_LANCZOS;
-                } else if (w->screen() != screen)
-                    quadsAdded = true; // we don't want parts of overlapping windows on the other screen
-                if (w->isDesktop())
-                    quadsAdded = false;
-            }
-            if (!quadsAdded) {
-                foreach (const WindowQuad & quad, data.quads) {
-                    QRect quadRect(
-                        w->x() + quad.left(), w->y() + quad.top(),
-                        quad.right() - quad.left(), quad.bottom() - quad.top()
-                    );
-                    if (quadRect.intersects(screenGeom))
-                        screenQuads.append(quad);
+                } else if (w->screen() != screen) {
+                    continue; // we don't want parts of overlapping windows on the other screen
                 }
-            }
-            if (screenQuads.isEmpty())
+                if (w->isDesktop() && !transformedGeo.intersects(screenGeom)) {
+                    continue;
+                }
+            } else if (!transformedGeo.intersects(screenGeom)) {
                 continue; // Nothing is being displayed, don't bother
+            }
             WindowPaintData d = data;
-            d.quads = screenQuads;
 
             QPointF newPos = scalePos(transformedGeo.topLeft().toPoint(), paintingDesktop, screen);
             double progress = timeline.currentValue();