Store GLRenderTarget::scale

Summary:
GLRenderTarget already stores the translation from global compositor
space to the render target co-ordinates, we also need a scale factor for
the exact same reasons.

Test Plan: Used in various effects after this patch and it works there.

Reviewers: #plasma

Subscribers: plasma-devel, kwin, #kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D4948

libkwineffects/kwinglutils.cpp

@@ -1037,6 +1037,7 @@ bool GLRenderTarget::s_blitSupported = false;
 QStack<GLRenderTarget*> GLRenderTarget::s_renderTargets = QStack<GLRenderTarget*>();
 QSize GLRenderTarget::s_virtualScreenSize;
 QRect GLRenderTarget::s_virtualScreenGeometry;
+qreal GLRenderTarget::s_virtualScreenScale = 1.0;
 
 void GLRenderTarget::initStatic()
 {

libkwineffects/kwinglutils.h

@@ -505,6 +505,21 @@ public:
         return s_virtualScreenGeometry;
     }
 
+    /**
+     * The scale of the OpenGL window currently being rendered to
+     *
+     * @returns the ratio between the virtual geometry space the rendering
+     * system uses and the target
+     * @since 5.10
+     */
+    static void setVirtualScreenScale(qreal scale) {
+        s_virtualScreenScale = scale;
+    }
+
+    static qreal virtualScreenScale() {
+        return s_virtualScreenScale;
+    }
+
 
 protected:
     void initFBO();
@@ -518,6 +533,7 @@ private:
     static QStack<GLRenderTarget*> s_renderTargets;
     static QSize s_virtualScreenSize;
     static QRect s_virtualScreenGeometry;
+    static qreal s_virtualScreenScale;
 
     GLTexture mTexture;
     bool mValid;

scene_opengl.cpp

@@ -700,6 +700,7 @@ qint64 SceneOpenGL::paint(QRegion damage, ToplevelList toplevels)
             QRegion repaint = m_backend->prepareRenderingForScreen(i);
             GLVertexBuffer::setVirtualScreenGeometry(geo);
             GLRenderTarget::setVirtualScreenGeometry(geo);
+            GLRenderTarget::setVirtualScreenScale(screens()->scale(i));
 
             const GLenum status = glGetGraphicsResetStatus();
             if (status != GL_NO_ERROR) {
@@ -728,6 +729,7 @@ qint64 SceneOpenGL::paint(QRegion damage, ToplevelList toplevels)
         }
         GLVertexBuffer::setVirtualScreenGeometry(screens()->geometry());
         GLRenderTarget::setVirtualScreenGeometry(screens()->geometry());
+        GLRenderTarget::setVirtualScreenScale(1);
 
         int mask = 0;
         updateProjectionMatrix();