plugins/backgroundcontrast: fix transformations

While the GLFramebuffer::blitFromRenderTarget helper un-applies the transformations
the rendertarget has, the effect is not written with that in mind. In order to keep
it working properly, blit without any transformations and only adjust the coordinate
system difference between texture and fbo

src/plugins/backgroundcontrast/contrast.cpp

@@ -453,10 +453,7 @@ void ContrastEffect::doContrast(const RenderTarget &renderTarget, const RenderVi
     GLTexture *contrastTexture = windowData.texture.get();
     contrastTexture->bind();
 
-    const QRect logicalSourceRect = actualShape.boundingRect();
-    windowData.fbo->blitFromRenderTarget(renderTarget, viewport, logicalSourceRect, QRect(0, 0, contrastTexture->width(), contrastTexture->height()));
-
-    // Draw the texture on the offscreen framebuffer object, while blurring it horizontally
+    windowData.fbo->blitFromFramebuffer(r.toRect(), QRect(QPoint(), contrastTexture->size()));
 
     m_shader->setColorMatrix(m_windowData[w].colorMatrix);
     m_shader->bind();
@@ -471,6 +468,8 @@ void ContrastEffect::doContrast(const RenderTarget &renderTarget, const RenderVi
     textureMatrix *= renderTarget.transformation();
     textureMatrix.translate(-0.5, -0.5);
     // scaled logical to texture coordinates
+    textureMatrix.scale(1, -1);
+    textureMatrix.translate(0, -1);
     textureMatrix.scale(1.0 / boundingRect.width(), 1.0 / boundingRect.height(), 1);
     textureMatrix.translate(-boundingRect.x(), -boundingRect.y(), 0);
     textureMatrix.scale(1.0 / viewport.scale(), 1.0 / viewport.scale());