added function_grapher

docs/lib-function_grapher.md

@@ -0,0 +1,116 @@
+# function_grapher
+
+Given a set of points `[x, y, f(x, y)]` where `f(x, y)` is a mathematics function, the `function_grapher` module can create the graph of `f(x, y)`.
+
+It depends on the `line3d` and `polyline3d` modules so you have to include "line3d.scad" and "polyline3d.scad".
+
+## Parameters
+
+- `points` : A set of points `[x, y, f(x, y)]`. See examples below.
+- `thickness` : The face or line thickness.
+- `style` : The style of the graph. It accepts `"FACES"`, `"LINES"` and `"HULL_FACES"`. The default value is `"FACES"` which simply takes `f(x, y) - thickness` for each point to build a bottom. It may cause thickness problems when slopes is high. The `"HULL_FACES"` value can solve the problem but is slow. When assigning `"LINES"`, it uses lines to connect points.
+- `slicing` : Given a rectangle, we have two ways to slice it into two triangles. Using this parameter to determine the way you want. It accepts `"SLASH"` (default) and `"BACK_SLASH"`.
+- `$fa`, `$fs`, `$fn` : Used by the `circle` or `sphere` module internally. It affects the speed of rending. For example, a large `$fn` may be very slow when rending. Check [the circle module](https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Using_the_2D_Subsystem#circle) or [the sphere module](https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Primitive_Solids#sphere) for more details. 
+
+## Examples
+
+	include <line3d.scad>;
+	include <polyline3d.scad>;
+	include <function_grapher.scad>;
+	
+	points = [
+	    [[0, 0, 1], [1, 0, 2], [2, 0, 2], [3, 0, 3]],
+	    [[0, 1, 1], [1, 1, 4], [2, 1, 0], [3, 1, 3]],
+	    [[0, 2, 1], [1, 2, 3], [2, 2, 1], [3, 2, 3]],
+	    [[0, 3, 1], [1, 3, 3], [2, 3, 1], [3, 3, 3]]
+	];
+	
+	thickness = 0.5;
+	
+	function_grapher(points, thickness);
+
+![function_grapher](images/lib-function_grapher-1.JPG)
+
+	include <line3d.scad>;
+	include <polyline3d.scad>;
+	include <function_grapher.scad>;
+	
+	function f(x, y) = 
+	   30 * (
+	       cos(sqrt(pow(x, 2) + pow(y, 2))) + 
+	       cos(3 * sqrt(pow(x, 2) + pow(y, 2)))
+	   );
+	
+	thickness = 2;
+	min_value =  -200;
+	max_value = 200;
+	resolution = 10;
+	
+	points = [
+	    for(y = [min_value:resolution:max_value])
+	        [
+	            for(x = [min_value:resolution:max_value]) 
+	                [x, y, f(x, y)]
+	        ]
+	];
+	
+	function_grapher(points, thickness);
+
+![function_grapher](images/lib-function_grapher-2.JPG)
+
+	include <line3d.scad>;
+	include <polyline3d.scad>;
+	include <function_grapher.scad>;
+
+	function f(x, y) = 
+	   30 * (
+	       cos(sqrt(pow(x, 2) + pow(y, 2))) + 
+	       cos(3 * sqrt(pow(x, 2) + pow(y, 2)))
+	   );
+	
+	thickness = 2;
+	min_value =  -200;
+	max_value = 200;
+	resolution = 10;
+	style = "LINES"; 
+	
+	points = [
+	    for(y = [min_value:resolution:max_value])
+	        [
+	            for(x = [min_value:resolution:max_value]) 
+	                [x, y, f(x, y)]
+	        ]
+	];
+	
+	function_grapher(points, thickness, style);
+
+![function_grapher](images/lib-function_grapher-3.JPG)
+
+	include <line3d.scad>;
+	include <polyline3d.scad>;
+	include <function_grapher.scad>;
+
+	function f(x, y) = 
+	   30 * (
+	       cos(sqrt(pow(x, 2) + pow(y, 2))) + 
+	       cos(3 * sqrt(pow(x, 2) + pow(y, 2)))
+	   );
+	
+	thickness = 2;
+	min_value =  -200;
+	max_value = 200;
+	resolution = 10;
+	style = "LINES"; 
+	slicing = "BACK_SLASH";
+	
+	points = [
+	    for(y = [min_value:resolution:max_value])
+	        [
+	            for(x = [min_value:resolution:max_value]) 
+	                [x, y, f(x, y)]
+	        ]
+	];
+	
+	function_grapher(points, thickness, style, slicing);
+
+![function_grapher](images/lib-function_grapher-4.JPG)