scene: Make ItemRenderer responsible for pushing fbo

It makes more sense for an output layer to return the render target fbo.
The user of the render target will then take appropriate steps to bind
the fbo. It reduces the amount of boilerplate code in output layers too.

src/backends/drm/drm_egl_layer_surface.cpp

@@ -96,9 +96,7 @@ std::optional<OutputLayerBeginFrameInfo> EglGbmLayerSurface::startRendering(cons
         }
     }
 
-    GLFramebuffer::pushFramebuffer(m_surface.gbmSurface->fbo());
     if (m_shadowBuffer) {
-        GLFramebuffer::pushFramebuffer(m_shadowBuffer->fbo());
         // the blit after rendering will completely overwrite the back buffer anyways
         return OutputLayerBeginFrameInfo{
             .renderTarget = RenderTarget(m_shadowBuffer->fbo()),
@@ -130,11 +128,11 @@ void EglGbmLayerSurface::aboutToStartPainting(DrmOutput *output, const QRegion &
 bool EglGbmLayerSurface::endRendering(DrmPlane::Transformations renderOrientation, const QRegion &damagedRegion)
 {
     if (m_shadowBuffer) {
-        GLFramebuffer::popFramebuffer();
+        GLFramebuffer::pushFramebuffer(m_surface.gbmSurface->fbo());
         // TODO handle bufferOrientation != Rotate0
         m_shadowBuffer->render(renderOrientation);
+        GLFramebuffer::popFramebuffer();
     }
-    GLFramebuffer::popFramebuffer();
     const auto gbmBuffer = m_surface.gbmSurface->swapBuffers(damagedRegion);
     if (!gbmBuffer) {
         return false;

src/backends/drm/drm_output.cpp

@@ -500,6 +500,9 @@ void DrmOutput::renderCursorOpengl(const RenderTarget &renderTarget, const QSize
     QMatrix4x4 mvp;
     mvp.ortho(QRect(QPoint(), renderTarget.size()));
 
+    GLFramebuffer *fbo = std::get<GLFramebuffer *>(renderTarget.nativeHandle());
+    GLFramebuffer::pushFramebuffer(fbo);
+
     glClearColor(0, 0, 0, 0);
     glClear(GL_COLOR_BUFFER_BIT);
 
@@ -512,6 +515,8 @@ void DrmOutput::renderCursorOpengl(const RenderTarget &renderTarget, const QSize
     m_cursor.texture->render(QRect(0, 0, cursorSize.width(), cursorSize.height()), renderTarget.devicePixelRatio());
     m_cursor.texture->unbind();
     glDisable(GL_BLEND);
+
+    GLFramebuffer::popFramebuffer();
 }
 
 void DrmOutput::renderCursorQPainter(const RenderTarget &renderTarget)

src/backends/drm/drm_virtual_egl_layer.cpp

@@ -69,7 +69,6 @@ std::optional<OutputLayerBeginFrameInfo> VirtualEglGbmLayer::beginFrame()
     if (!m_gbmSurface->makeContextCurrent()) {
         return std::nullopt;
     }
-    GLFramebuffer::pushFramebuffer(m_gbmSurface->fbo());
     return OutputLayerBeginFrameInfo{
         .renderTarget = RenderTarget(m_gbmSurface->fbo()),
         .repaint = m_gbmSurface->repaintRegion(),
@@ -78,7 +77,6 @@ std::optional<OutputLayerBeginFrameInfo> VirtualEglGbmLayer::beginFrame()
 
 bool VirtualEglGbmLayer::endFrame(const QRegion &renderedRegion, const QRegion &damagedRegion)
 {
-    GLFramebuffer::popFramebuffer();
     const auto buffer = m_gbmSurface->swapBuffers(damagedRegion);
     if (buffer) {
         m_currentBuffer = buffer;

src/backends/virtual/virtual_egl_backend.cpp

@@ -48,7 +48,6 @@ std::optional<OutputLayerBeginFrameInfo> VirtualEglLayer::beginFrame()
         m_fbo = std::make_unique<GLFramebuffer>(m_texture.get());
     }
 
-    GLFramebuffer::pushFramebuffer(m_fbo.get());
     return OutputLayerBeginFrameInfo{
         .renderTarget = RenderTarget(m_fbo.get()),
         .repaint = infiniteRegion(),
@@ -57,7 +56,6 @@ std::optional<OutputLayerBeginFrameInfo> VirtualEglLayer::beginFrame()
 
 bool VirtualEglLayer::endFrame(const QRegion &renderedRegion, const QRegion &damagedRegion)
 {
-    GLFramebuffer::popFramebuffer();
     return true;
 }
 

src/backends/wayland/wayland_egl_backend.cpp

@@ -197,7 +197,6 @@ std::optional<OutputLayerBeginFrameInfo> WaylandEglPrimaryLayer::beginFrame()
         repair = m_damageJournal.accumulate(m_buffer->age(), infiniteRegion());
     }
 
-    GLFramebuffer::pushFramebuffer(m_buffer->framebuffer());
     return OutputLayerBeginFrameInfo{
         .renderTarget = RenderTarget(m_buffer->framebuffer()),
         .repaint = repair,
@@ -207,7 +206,6 @@ std::optional<OutputLayerBeginFrameInfo> WaylandEglPrimaryLayer::beginFrame()
 bool WaylandEglPrimaryLayer::endFrame(const QRegion &renderedRegion, const QRegion &damagedRegion)
 {
     m_damageJournal.add(damagedRegion);
-    GLFramebuffer::popFramebuffer();
     return true;
 }
 
@@ -279,7 +277,6 @@ std::optional<OutputLayerBeginFrameInfo> WaylandEglCursorLayer::beginFrame()
         m_framebuffer = std::make_unique<GLFramebuffer>(m_texture.get());
     }
 
-    GLFramebuffer::pushFramebuffer(m_framebuffer.get());
     return OutputLayerBeginFrameInfo{
         .renderTarget = RenderTarget(m_framebuffer.get()),
         .repaint = infiniteRegion(),
@@ -288,8 +285,6 @@ std::optional<OutputLayerBeginFrameInfo> WaylandEglCursorLayer::beginFrame()
 
 bool WaylandEglCursorLayer::endFrame(const QRegion &renderedRegion, const QRegion &damagedRegion)
 {
-    GLFramebuffer::popFramebuffer();
-
     // Technically, we could pass a linux-dmabuf buffer, but host kwin does not support that atm.
     const QImage image = m_texture->toImage().mirrored(false, true);
     KWayland::Client::Buffer::Ptr buffer = m_output->backend()->display()->shmPool()->createBuffer(image);

src/backends/wayland/wayland_output.cpp

@@ -215,6 +215,9 @@ void WaylandOutput::renderCursorOpengl(WaylandEglBackend *backend, const QImage
     QMatrix4x4 mvp;
     mvp.ortho(QRect(QPoint(), beginInfo->renderTarget.size()));
 
+    GLFramebuffer *fbo = std::get<GLFramebuffer *>(beginInfo->renderTarget.nativeHandle());
+    GLFramebuffer::pushFramebuffer(fbo);
+
     glClearColor(0, 0, 0, 0);
     glClear(GL_COLOR_BUFFER_BIT);
 
@@ -231,6 +234,8 @@ void WaylandOutput::renderCursorOpengl(WaylandEglBackend *backend, const QImage
         glDisable(GL_BLEND);
     }
 
+    GLFramebuffer::popFramebuffer();
+
     cursorLayer->endFrame(infiniteRegion(), infiniteRegion());
 }
 

src/backends/x11/standalone/x11_standalone_egl_backend.cpp

@@ -165,8 +165,6 @@ OutputLayerBeginFrameInfo EglBackend::beginFrame()
 
     eglWaitNative(EGL_CORE_NATIVE_ENGINE);
 
-    // Push the default framebuffer to the render target stack.
-    GLFramebuffer::pushFramebuffer(m_fbo.get());
     return OutputLayerBeginFrameInfo{
         .renderTarget = RenderTarget(m_fbo.get()),
         .repaint = repaint,
@@ -199,9 +197,6 @@ void EglBackend::present(Output *output)
         }
     }
 
-    // Pop the default render target from the render target stack.
-    GLFramebuffer::popFramebuffer();
-
     presentSurface(surface(), effectiveRenderedRegion, workspace()->geometry());
 
     if (overlayWindow() && overlayWindow()->window()) { // show the window only after the first pass,

src/backends/x11/standalone/x11_standalone_glx_backend.cpp

@@ -783,7 +783,6 @@ OutputLayerBeginFrameInfo GlxBackend::beginFrame()
     QRegion repaint;
     makeCurrent();
 
-    GLFramebuffer::pushFramebuffer(m_fbo.get());
     if (supportsBufferAge()) {
         repaint = m_damageJournal.accumulate(m_bufferAge, infiniteRegion());
     }
@@ -823,8 +822,6 @@ void GlxBackend::present(Output *output)
         effectiveRenderedRegion = displayRect;
     }
 
-    GLFramebuffer::popFramebuffer();
-
     present(effectiveRenderedRegion);
 
     if (overlayWindow()->window()) { // show the window only after the first pass,

src/backends/x11/windowed/x11_windowed_egl_backend.cpp

@@ -41,7 +41,6 @@ std::optional<OutputLayerBeginFrameInfo> X11WindowedEglPrimaryLayer::beginFrame(
 {
     eglMakeCurrent(m_backend->eglDisplay(), m_eglSurface, m_eglSurface, m_backend->context());
     ensureFbo();
-    GLFramebuffer::pushFramebuffer(m_fbo.get());
 
     QRegion repaint = m_output->exposedArea() + m_output->rect();
     m_output->clearExposedArea();
@@ -55,7 +54,6 @@ std::optional<OutputLayerBeginFrameInfo> X11WindowedEglPrimaryLayer::beginFrame(
 bool X11WindowedEglPrimaryLayer::endFrame(const QRegion &renderedRegion, const QRegion &damagedRegion)
 {
     m_lastDamage = damagedRegion;
-    GLFramebuffer::popFramebuffer();
     return true;
 }
 
@@ -112,7 +110,6 @@ std::optional<OutputLayerBeginFrameInfo> X11WindowedEglCursorLayer::beginFrame()
         m_framebuffer = std::make_unique<GLFramebuffer>(m_texture.get());
     }
 
-    GLFramebuffer::pushFramebuffer(m_framebuffer.get());
     return OutputLayerBeginFrameInfo{
         .renderTarget = RenderTarget(m_framebuffer.get()),
         .repaint = infiniteRegion(),
@@ -121,8 +118,6 @@ std::optional<OutputLayerBeginFrameInfo> X11WindowedEglCursorLayer::beginFrame()
 
 bool X11WindowedEglCursorLayer::endFrame(const QRegion &renderedRegion, const QRegion &damagedRegion)
 {
-    GLFramebuffer::popFramebuffer();
-
     const QImage buffer = m_texture->toImage().mirrored(false, true);
     m_output->cursor()->update(buffer, m_hotspot);
 

src/backends/x11/windowed/x11_windowed_output.cpp

@@ -315,6 +315,9 @@ void X11WindowedOutput::renderCursorOpengl(X11WindowedEglBackend *backend, const
     QMatrix4x4 mvp;
     mvp.ortho(QRect(QPoint(), beginInfo->renderTarget.size()));
 
+    GLFramebuffer *fbo = std::get<GLFramebuffer *>(beginInfo->renderTarget.nativeHandle());
+    GLFramebuffer::pushFramebuffer(fbo);
+
     glClearColor(0, 0, 0, 0);
     glClear(GL_COLOR_BUFFER_BIT);
 
@@ -331,6 +334,8 @@ void X11WindowedOutput::renderCursorOpengl(X11WindowedEglBackend *backend, const
         glDisable(GL_BLEND);
     }
 
+    GLFramebuffer::popFramebuffer();
+
     cursorLayer->endFrame(infiniteRegion(), infiniteRegion());
 }
 

src/scene/itemrenderer_opengl.cpp

@@ -20,12 +20,16 @@ ItemRendererOpenGL::ItemRendererOpenGL()
 
 void ItemRendererOpenGL::beginFrame(RenderTarget *renderTarget)
 {
+    GLFramebuffer *fbo = std::get<GLFramebuffer *>(renderTarget->nativeHandle());
+    GLFramebuffer::pushFramebuffer(fbo);
+
     GLVertexBuffer::streamingBuffer()->beginFrame();
 }
 
 void ItemRendererOpenGL::endFrame()
 {
     GLVertexBuffer::streamingBuffer()->endOfFrame();
+    GLFramebuffer::popFramebuffer();
 }
 
 QVector4D ItemRendererOpenGL::modulate(float opacity, float brightness) const