Virtio GPU is something different, namely a para-virtualized graphics adapter that uses the VirtIO guest-to-host communication to expose hardware accelerated graphics to the VM.

For instance, on the guest side, you could have Mesa3D implementing OpenGL userspace and internally using its "Virgl" driver (or "Venus", for Vulkan) that serializes a command stream, sends that through a guest side kernel driver that passes it on through the VirtIO device to Qemu on the host side, that then uses existing OpenGL userspace graphics APIs to do the actual accelerated rendering.