Add sky light, physical atmosphere, auto exposure and bloom to the GL 4.6 renderer

gl/readback.h

@@ -0,0 +1,40 @@
+#pragma once
+
+#include <array>
+#include <memory>
+
+#include "object.h"
+#include "fence.h"
+
+namespace gl
+{
+	// copies of a small range of a buffer the gpu writes, for the cpu to read a few frames later without waiting for the
+	// gpu: a queue of buffers, each with the fence of the copy into it. if the gpu is so far behind that every buffer is
+	// still waiting, the copy is skipped
+	class readback
+	{
+	  public:
+		explicit readback(GLsizeiptr size);
+		~readback();
+		readback(const readback &) = delete;
+		readback &operator=(const readback &) = delete;
+
+		// queues a copy of size bytes of Source, from Offset
+		void push(GLuint Source, GLintptr Offset = 0);
+		// writes the newest copy which the gpu has finished to Data and returns true; false if none was finished since the last call
+		bool pop(void *Data);
+
+	  private:
+		static constexpr size_t SLOTS = 4;
+		struct slot
+		{
+			GLuint buffer = 0;
+			std::unique_ptr<fence> copied;
+		};
+		GLsizeiptr m_size;
+		std::array<slot, SLOTS> m_slots;
+		// oldest slot in use and the number of slots in use
+		size_t m_first = 0;
+		size_t m_used = 0;
+	};
+} // namespace gl