core: rename mbgl directories to mln (#4511)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

include/mln/gl/renderer_backend.hpp

@@ -0,0 +1,62 @@
+#pragma once
+
+#include <mln/gfx/renderer_backend.hpp>
+#include <mln/util/image.hpp>
+#include <mln/util/size.hpp>
+#include <mln/util/util.hpp>
+
+namespace mln {
+
+class ProgramParameters;
+
+namespace gl {
+
+using ProcAddress = void (*)();
+using FramebufferID = uint32_t;
+
+class RendererBackend : public gfx::RendererBackend {
+public:
+    RendererBackend(gfx::ContextMode);
+    RendererBackend(gfx::ContextMode, const TaggedScheduler&);
+    ~RendererBackend() override;
+
+    /// Called prior to rendering to update the internally assumed OpenGL state.
+    virtual void updateAssumedState() = 0;
+
+    /// One-time shader initialization
+    void initShaders(gfx::ShaderRegistry&, const ProgramParameters& programParameters) override;
+
+protected:
+    std::unique_ptr<gfx::Context> createContext() override;
+
+    /// Called with the name of an OpenGL extension that should be loaded.
+    /// RendererBackend implementations must call the API-specific version that
+    /// obtains the function pointer for this function, or a null pointer if
+    /// unsupported/unavailable.
+    virtual ProcAddress getExtensionFunctionPointer(const char*) = 0;
+
+    /// Reads the color pixel data from the currently bound framebuffer.
+    PremultipliedImage readFramebuffer(const Size&);
+
+    /// A constant to signal that a framebuffer is bound, but with an unknown ID.
+    static constexpr const FramebufferID ImplicitFramebufferBinding = std::numeric_limits<FramebufferID>::max();
+
+    /// Tells the renderer that OpenGL state has already been set by the windowing toolkit.
+    /// It sets the internal assumed state to the supplied values.
+    void assumeFramebufferBinding(FramebufferID fbo);
+    void assumeViewport(int32_t x, int32_t y, const Size&);
+    void assumeScissorTest(int32_t, int32_t, uint32_t, uint32_t);
+
+    /// Returns true when assumed framebuffer binding hasn't changed from the implicit binding.
+    bool implicitFramebufferBound();
+
+public:
+    /// Triggers an OpenGL state update if the internal assumed state doesn't
+    /// match the supplied values.
+    void setFramebufferBinding(FramebufferID fbo);
+    void setViewport(int32_t x, int32_t y, const Size&);
+    void setScissorTest(int32_t, int32_t, uint32_t, uint32_t);
+};
+
+} // namespace gl
+} // namespace mln