Add new variants of love.graphics.clear for controlling how the depth and stencil buffers are cleared.

- Add love.graphics.clear(r, g, b, a [, stencilvalue, depthvalue]).
- Add love.graphics.clear(color1, color2, …, [, stencilvalue, depthvalue]).
- Add love.graphics.clear(false, stencilvalue, depthvalue).

stencilvalue and depthvalue are either true, false, or a number. True is the default behaviour and clears that buffer to the default value (0 for stencil, 1 for depth), false prevents clearing.

The third variant listed above only clears the depth and/or stencil buffers and not the color buffer.

--HG--
branch : minor

src/common/Optional.h

@@ -0,0 +1,52 @@
+/**
+ * Copyright (c) 2006-2017 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
+
+namespace love
+{
+
+// Currently only meant for simple types.
+template <typename T>
+struct Optional
+{
+	bool hasValue;
+	T value;
+
+	Optional()
+		: hasValue(false)
+		, value(T())
+	{}
+
+	Optional(T val)
+		: hasValue(true)
+		, value(val)
+	{}
+
+private:
+
+};
+
+typedef Optional<bool> OptionalBool;
+typedef Optional<float> OptionalFloat;
+typedef Optional<double> OptionalDouble;
+typedef Optional<int> OptionalInt;
+
+} // love