Hook up the PS2MouseDevice to the AbstractScreen+WindowManager.

Render the mouse cursor by xor'ing the pixels. I don't know anything about
hardware cursors yet and this way we don't need to recompose the window
hierarchy every time you move the mouse. :^)

Kernel/PS2MouseDevice.cpp

@@ -1,10 +1,13 @@
 #include "PS2MouseDevice.h"
 #include "IO.h"
 
+static PS2MouseDevice* s_the;
+
 PS2MouseDevice::PS2MouseDevice()
     : IRQHandler(12)
     , CharacterDevice(10, 1)
 {
+    s_the = this;
     initialize();
 }
 
@@ -12,6 +15,11 @@ PS2MouseDevice::~PS2MouseDevice()
 {
 }
 
+PS2MouseDevice& PS2MouseDevice::the()
+{
+    return *s_the;
+}
+
 void PS2MouseDevice::handle_irq()
 {
     byte data = IO::in8(0x60);
@@ -32,6 +40,8 @@ void PS2MouseDevice::handle_irq()
             (m_data[0] & 1) ? "Left" : "",
             (m_data[0] & 2) ? "Right" : ""
         );
+        if (m_client)
+            m_client->did_receive_mouse_data(m_data[1], -m_data[2], m_data[0] & 1, m_data[0] & 2);
         break;
     }
 }
@@ -120,3 +130,7 @@ ssize_t PS2MouseDevice::write(const byte *buffer, size_t buffer_size)
     ASSERT_NOT_REACHED();
     return 0;
 }
+
+MouseClient::~MouseClient()
+{
+}

Kernel/PS2MouseDevice.h

@@ -3,11 +3,17 @@
 #include <VirtualFileSystem/CharacterDevice.h>
 #include "IRQHandler.h"
 
+class MouseClient;
+
 class PS2MouseDevice final : public IRQHandler, public CharacterDevice {
 public:
     PS2MouseDevice();
     virtual ~PS2MouseDevice() override;
 
+    static PS2MouseDevice& the();
+
+    void set_client(MouseClient* client) { m_client = client; }
+
 private:
     virtual bool has_data_available_for_reading() const override;
     virtual ssize_t read(byte* buffer, size_t buffer_size) override;
@@ -23,6 +29,13 @@ private:
     void wait_then_write(byte port, byte data);
     byte wait_then_read(byte port);
 
+    MouseClient* m_client { nullptr };
     byte m_data_state { 0 };
     signed_byte m_data[3];
 };
+
+class MouseClient {
+public:
+    virtual ~MouseClient();
+    virtual void did_receive_mouse_data(int dx, int dy, bool left_button, bool right_button) = 0;
+};