fix: reduce shader usage and fix greeter

Plugins/ZShell/Internal/wallpaperservice.cpp

@@ -662,6 +662,17 @@ void WallpaperService::drawSurface(WallpaperSurface* surface) {
 		return;
 	}
 
+	// Release the context when this scope ends (see FrameService::drawSurface).
+	// Holding it across the draw loop's sleep serializes the two raw-EGL clients on
+	// NVIDIA, which makes eglSwapBuffers fail and starves other processes' contexts.
+	struct ContextRelease {
+		EGLDisplay display;
+		~ContextRelease() {
+			eglMakeCurrent(
+				display, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT);
+		}
+	} contextRelease{m_eglDisplay};
+
 	QVariantMap crops;
 	QSize size;
 	bool upload = false;
@@ -701,7 +712,9 @@ void WallpaperService::drawSurface(WallpaperSurface* surface) {
 	glDrawArrays(GL_TRIANGLES, 0, 3);
 
 	if (!eglSwapBuffers(m_eglDisplay, target))
-		qWarning() << "WallpaperService: eglSwapBuffers failed";
+		qWarning()
+			<< "WallpaperService: eglSwapBuffers failed, eglGetError = 0x"
+			<< QString::number(unsigned(eglGetError()), 16);
 }
 
 void WallpaperService::addSurface(const QString& screen) {