shader graph : add dissolve node

hrt/shgraph/nodes/Dissolve.hx

@@ -0,0 +1,24 @@
+package hrt.shgraph.nodes;
+
+using hxsl.Ast;
+
+@name("Dissolve")
+@description("Dissolve input")
+@width(150)
+@group("Math")
+class Dissolve extends ShaderNodeHxsl {
+
+	static var SRC = {
+		@sginput(1.0) var channel : Float;
+		@sginput(1.0) var progress : Float;
+		@sginput(0.0) var saturation : Float;
+		@sginput(1.0) var width : Float;
+		@sgoutput var output : Float;
+
+		function fragment() {
+			var edge = mix(1.0 + width, -width, progress);
+			var ramp = saturate((1.0 + saturation) * (width - abs(edge - channel)) / width);
+			output = channel * ramp;
+		}
+	};
+}