Refactor Buffer internals.

Allows buffers created with love.graphics.newBuffer to only allocate VRAM data. Previously they had a copy of their contents in RAM.
Also makes it easier to implement Buffers in other graphics APIs and to implement more types of Buffers in the future.

src/common/Range.h

@@ -0,0 +1,83 @@
+/**
+ * Copyright (c) 2006-2020 LOVE Development Team
+ *
+ * This software is provided 'as-is', without any express or implied
+ * warranty.  In no event will the authors be held liable for any damages
+ * arising from the use of this software.
+ *
+ * Permission is granted to anyone to use this software for any purpose,
+ * including commercial applications, and to alter it and redistribute it
+ * freely, subject to the following restrictions:
+ *
+ * 1. The origin of this software must not be misrepresented; you must not
+ *    claim that you wrote the original software. If you use this software
+ *    in a product, an acknowledgment in the product documentation would be
+ *    appreciated but is not required.
+ * 2. Altered source versions must be plainly marked as such, and must not be
+ *    misrepresented as being the original software.
+ * 3. This notice may not be removed or altered from any source distribution.
+ **/
+
+#pragma once
+
+#include <stddef.h>
+#include <algorithm>
+#include <limits>
+
+namespace love
+{
+
+struct Range
+{
+	size_t first;
+	size_t last;
+
+	Range()
+		: first(std::numeric_limits<size_t>::max())
+		, last(0)
+	{}
+
+	Range(size_t offset, size_t size)
+		: first(offset)
+		, last(offset + size - 1)
+	{}
+
+	bool isValid() const { return first <= last; }
+
+	void invalidate()
+	{
+		first = std::numeric_limits<size_t>::max();
+		last = 0;
+	}
+
+	size_t getMin() const { return first; }
+	size_t getMax() const { return last; }
+
+	size_t getOffset() const { return first; }
+	size_t getSize() const { return (last - first) + 1; }
+
+	bool contains(const Range &other) const
+	{
+		return first <= other.first && last >= other.last;
+	}
+
+	void encapsulate(size_t index)
+	{
+		first = std::min(first, index);
+		last = std::max(last, index);
+	}
+
+	void encapsulate(size_t offset, size_t size)
+	{
+		first = std::min(first, offset);
+		last = std::max(last, offset + size - 1);
+	}
+
+	void encapsulate(const Range &other)
+	{
+		first = std::min(first, other.first);
+		last = std::max(last, other.last);
+	}
+};
+
+} // love