Added new sample to demonstrate negative viewport height via VK_KHR_MAINTENANCE1

Refs #563

data/shaders/negativeviewportheight/quad.frag

@@ -0,0 +1,12 @@
+#version 450
+
+layout (binding = 0) uniform sampler2D samplerColor;
+
+layout (location = 0) in vec2 inUV;
+layout (location = 0) out vec4 outColor;
+
+void main() 
+{
+	outColor = texture(samplerColor, inUV);
+	outColor.rgb *= vec3(inUV, 0.0f);
+}

data/shaders/negativeviewportheight/quad.vert

@@ -0,0 +1,14 @@
+#version 450
+
+layout (location = 0) in vec3 inPos;
+layout (location = 1) in vec2 inUV;
+
+layout (location = 0) out vec2 outUV;
+
+void main() 
+{
+//	outUV = vec2((gl_VertexIndex << 1) & 2, gl_VertexIndex & 2);
+//	gl_Position = vec4(outUV * 2.0f - 1.0f, 0.0f, 1.0f);
+	outUV = inUV;
+	gl_Position = vec4(inPos, 1.0f);
+}