add offscreen render support to xrender

REVIEW: 104151
cherry-picked from b9534b4ca82973c2e99451b2e151241fd1b6e7cb

libkwineffects/kwinxrenderutils.cpp

@@ -23,6 +23,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #ifdef KWIN_HAVE_XRENDER_COMPOSITING
 
+#include <QStack>
 #include <QVector>
 #include <QPixmap>
 #include <QPainter>
@@ -212,6 +213,55 @@ XRenderPicture::XRenderPicture(Pixmap pix, int depth)
 {
 }
 
+static QPixmap *s_offscreenTarget = 0;
+static QStack<XRenderPicture*> s_scene_offscreenTargetStack;
+static int s_renderOffscreen = 0;
+
+void scene_setXRenderOffscreenTarget(QPixmap *pix)
+{
+    s_offscreenTarget = pix;
+}
+
+XRenderPicture *scene_xRenderOffscreenTarget()
+{
+    return s_scene_offscreenTargetStack.isEmpty() ? 0 : s_scene_offscreenTargetStack.top();
+}
+
+void setXRenderOffscreen(bool b)
+{
+    b ? ++s_renderOffscreen : --s_renderOffscreen;
+    if (s_renderOffscreen < 0) {
+        s_renderOffscreen = 0;
+        qWarning("*** SOMETHING IS MESSED UP WITH YOUR setXRenderOffscreen() USAGE ***");
+    }
+}
+
+void xRenderPushTarget(XRenderPicture *pic)
+{
+    s_scene_offscreenTargetStack.push(pic);
+    ++s_renderOffscreen;
+}
+
+void xRenderPopTarget()
+{
+    s_scene_offscreenTargetStack.pop();
+    --s_renderOffscreen;
+    if (s_renderOffscreen < 0) {
+        s_renderOffscreen = 0;
+        qWarning("*** SOMETHING IS MESSED UP WITH YOUR xRenderPopTarget() USAGE ***");
+    }
+}
+
+bool xRenderOffscreen()
+{
+    return s_renderOffscreen;
+}
+
+QPixmap *xRenderOffscreenTarget()
+{
+    return s_offscreenTarget;
+}
+
 } // namespace
 
 #endif

libkwineffects/kwinxrenderutils.h

@@ -126,6 +126,42 @@ KWIN_EXPORT XRenderPicture xRenderBlendPicture(double opacity);
 KWIN_EXPORT XRenderPicture xRenderFill(const XRenderColor *c);
 KWIN_EXPORT XRenderPicture xRenderFill(const QColor &c);
 
+/**
+ * Allows to render a window into a (transparent) pixmap
+ * NOTICE: the result can be queried as xRenderWindowOffscreenTarget()
+ * NOTICE: it may be 0
+ * NOTICE: when done call setXRenderWindowOffscreen(false) to continue normal render process
+ */
+KWIN_EXPORT void setXRenderOffscreen(bool b);
+
+/**
+ * Allows to define a persistent effect member as render target
+ * The window (including shadows) is rendered into the top left corner
+ * NOTICE: do NOT call setXRenderOffscreen(true) in addition!
+ * NOTICE: do not forget to xRenderPopTarget once you're done to continue the normal render process
+ */
+KWIN_EXPORT void xRenderPushTarget(XRenderPicture *pic);
+KWIN_EXPORT void xRenderPopTarget();
+
+/**
+ * Whether windows are currently rendered into an offscreen target buffer
+ */
+KWIN_EXPORT bool xRenderOffscreen();
+/**
+ * The offscreen buffer as set by the renderer because of setXRenderWindowOffscreen(true)
+ */
+KWIN_EXPORT QPixmap *xRenderOffscreenTarget();
+
+/**
+ * NOTICE: HANDS OFF!!!
+ * scene_setXRenderWindowOffscreenTarget() is ONLY to be used by the renderer - DO NOT TOUCH!
+ */
+KWIN_EXPORT void scene_setXRenderOffscreenTarget(QPixmap *pix);
+/**
+ * scene_xRenderWindowOffscreenTarget() is used by the scene to figure the target set by an effect
+ */
+KWIN_EXPORT XRenderPicture *scene_xRenderOffscreenTarget();
+
 } // namespace
 
 #endif

scene_xrender.cpp

@@ -417,8 +417,10 @@ void SceneXrender::Window::prepareTempPixmap()
         XFreePixmap(display(), temp_pixmap->handle());   // The picture owns the pixmap now
     if (!temp_pixmap)
         temp_pixmap = new QPixmap(r.width(), r.height());
-    else if (temp_pixmap->width() < r.width() || temp_pixmap->height() < r.height())
+    else if (temp_pixmap->width() < r.width() || temp_pixmap->height() < r.height()) {
         *temp_pixmap = QPixmap(r.width(), r.height());
+        scene_setXRenderOffscreenTarget(0); // invalidate, better crash than cause weird results for developers
+    }
     if (Extensions::nonNativePixmaps()) {
         Pixmap pix = XCreatePixmap(display(), rootWindow(), temp_pixmap->width(), temp_pixmap->height(), DefaultDepth(display(), DefaultScreen(display())));
         *temp_pixmap = QPixmap::fromX11Pixmap(pix);
@@ -532,12 +534,16 @@ void SceneXrender::Window::performPaint(int mask, QRegion region, WindowPaintDat
     // the window has border
     // This solves a number of glitches and on top of this
     // it optimizes painting quite a bit
-    const bool blitInTempPixmap = scaled && (wantShadow || (client && !client->noBorder()) || (deleted && !deleted->noBorder()));
-    Picture renderTarget = buffer;
+    const bool blitInTempPixmap = xRenderOffscreen() || (scaled && (wantShadow || (client && !client->noBorder()) || (deleted && !deleted->noBorder())));
 
+    Picture renderTarget = buffer;
     if (blitInTempPixmap) {
-        prepareTempPixmap();
-        renderTarget = temp_pixmap->x11PictureHandle();
+        if (scene_xRenderOffscreenTarget())
+            renderTarget = *scene_xRenderOffscreenTarget();
+        else {
+            prepareTempPixmap();
+            renderTarget = temp_pixmap->x11PictureHandle();
+        }
     } else {
         XRenderSetPictureTransform(display(), pic, &xform);
         if (filter == ImageFilterGood) {
@@ -702,6 +708,8 @@ XRenderComposite(display(), PictOpOver, _PART_->x11PictureHandle(), decorationAl
             XRenderChangePicture(display(), pic, CPRepeat, &attr);
         }
     }
+    if (xRenderOffscreen())
+        scene_setXRenderOffscreenTarget(temp_pixmap);
 }
 
 void SceneXrender::screenGeometryChanged(const QSize &size)