Allow specifying a render target scale for windows

This allows overriding the render target scale when rendering windows
and makes use of it in the screencasting plugin.

src/effects/screenshot/screenshot.cpp

@@ -246,6 +246,7 @@ void ScreenShotEffect::takeScreenShot(ScreenShotWindowData *screenshot)
     if (validTarget) {
         d.setXTranslation(-geometry.x());
         d.setYTranslation(-geometry.y());
+        d.setRenderTargetScale(devicePixelRatio);
 
         // render window into offscreen texture
         int mask = PAINT_WINDOW_TRANSFORMED | PAINT_WINDOW_TRANSLUCENT;

src/libkwineffects/kwineffects.cpp

@@ -233,6 +233,7 @@ public:
     qreal crossFadeProgress;
     QMatrix4x4 pMatrix;
     QMatrix4x4 screenProjectionMatrix;
+    std::optional<qreal> renderTargetScale = std::nullopt;
 };
 
 WindowPaintData::WindowPaintData()
@@ -411,6 +412,16 @@ QMatrix4x4 WindowPaintData::screenProjectionMatrix() const
     return d->screenProjectionMatrix;
 }
 
+std::optional<qreal> WindowPaintData::renderTargetScale() const
+{
+    return d->renderTargetScale;
+}
+
+void WindowPaintData::setRenderTargetScale(qreal scale)
+{
+    d->renderTargetScale = scale;
+}
+
 class ScreenPaintData::Private
 {
 public:

src/libkwineffects/kwineffects.h

@@ -39,6 +39,7 @@
 
 #include <climits>
 #include <functional>
+#include <optional>
 
 class KConfigGroup;
 class QFont;
@@ -3300,6 +3301,15 @@ public:
      */
     QMatrix4x4 screenProjectionMatrix() const;
 
+    /**
+     * An override for the scale the window should be rendered at.
+     *
+     * When set, this value will be used instead of the window's output scale
+     * when rendering.
+     */
+    std::optional<qreal> renderTargetScale() const;
+    void setRenderTargetScale(qreal scale);
+
     /**
      * Shader to be used for rendering, if any.
      */

src/plugins/screencast/windowscreencastsource.cpp

@@ -50,15 +50,14 @@ void WindowScreenCastSource::render(QImage *image)
 
 void WindowScreenCastSource::render(GLFramebuffer *target)
 {
-    auto targetScale = Compositor::self()->scene()->renderTargetScale();
-
-    const QRectF geometry = scaledRect(m_window->clientGeometry(), targetScale);
+    const QRectF geometry = m_window->clientGeometry();
     QMatrix4x4 projectionMatrix;
     projectionMatrix.ortho(geometry.x(), geometry.x() + geometry.width(),
                            geometry.y(), geometry.y() + geometry.height(), -1, 1);
 
     WindowPaintData data;
     data.setProjectionMatrix(projectionMatrix);
+    data.setRenderTargetScale(1.0);
 
     GLFramebuffer::pushFramebuffer(target);
     glClearColor(0.0, 0.0, 0.0, 0.0);

src/scenes/opengl/scene_opengl.cpp

@@ -429,7 +429,7 @@ void SceneOpenGL::render(Item *item, int mask, const QRegion &region, const Wind
     RenderContext renderContext{
         .clip = region,
         .hardwareClipping = region != infiniteRegion() && ((mask & Scene::PAINT_WINDOW_TRANSFORMED) || (mask & Scene::PAINT_SCREEN_TRANSFORMED)),
-        .renderTargetScale = renderTargetScale(),
+        .renderTargetScale = data.renderTargetScale().value_or(renderTargetScale()),
     };
 
     renderContext.transformStack.push(QMatrix4x4());