Support retrieving available GPU memory size

libs/gfx/include/psemek/gfx/memory.hpp

@@ -0,0 +1,11 @@
+#pragma once
+
+#include <cstddef>
+#include <optional>
+
+namespace psemek::gfx
+{
+
+	std::optional<std::size_t> available_memory();
+
+}

libs/gfx/source/memory.cpp

@@ -0,0 +1,29 @@
+#include <psemek/gfx/memory.hpp>
+#include <psemek/gfx/gl.hpp>
+
+namespace psemek::gfx
+{
+
+	std::optional<std::size_t> available_memory()
+	{
+		static bool const nvx = gl::sys::has_extension("GL_NVX_gpu_memory_info");
+		static bool const ati = gl::sys::has_extension("GL_ATI_meminfo");
+
+		if (nvx)
+		{
+			GLint value = 0;
+			gl::GetIntegerv(0x9049, &value);
+			return static_cast<std::size_t>(value) * 1024;
+		}
+
+		if (ati)
+		{
+			GLint values[4]{};
+			gl::GetIntegerv(0x87FC, values);
+			return static_cast<std::size_t>(values[0]) * 1024;
+		}
+
+		return std::nullopt;
+	}
+
+}