LibGL: Implement basic texture units

These are merely a way to hold the different texture target bind
points that a texture can be bound to.

Userland/Libraries/LibGL/Tex/TextureUnit.h

@@ -0,0 +1,31 @@
+/*
+ * Copyright (c) 2021, Jesse Buhagiar <jooster669@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/OwnPtr.h>
+#include <LibGL/Tex/Texture2D.h>
+
+namespace GL {
+
+class TextureUnit {
+public:
+    TextureUnit() = default;
+
+    void bind_texture_to_target(GLenum texture_target, const RefPtr<Texture>& texture);
+    void unbind_texture(GLenum texture_target);
+    const RefPtr<Texture>& get_bound_texture() const { return m_currently_bound_texture; }
+
+    GLenum currently_bound_target() const { return m_currently_bound_target; }
+    bool is_bound() const { return m_currently_bound_texture != nullptr; }
+
+private:
+    RefPtr<Texture2D> m_texture_target_2d { nullptr };
+    RefPtr<Texture> m_currently_bound_texture { nullptr };
+    GLenum m_currently_bound_target;
+};
+
+}