added bezier_surface.scad

src/bezier_surface.scad

@@ -0,0 +1,10 @@
+function bezier_surface(t_step, ctrl_pts) =
+    let(pts =  [
+        for(i = [0:len(ctrl_pts) - 1]) 
+            bezier_curve(t_step, ctrl_pts[i])
+    ]) 
+    [for(x = [0:len(pts[0]) - 1]) 
+        bezier_curve(t_step,  
+                [for(y = [0:len(pts) - 1]) pts[y][x]]
+        ) 
+    ];

src/test.scad

@@ -0,0 +1,66 @@
+include <hull_polyline3d.scad>;
+include <bezier_curve.scad>;
+include <bezier_surface.scad>; 
+include <function_grapher.scad>;
+
+t_step = 0.05;
+thickness = 0.5;
+
+ctrl_pts = [
+    [[0, 0, 20], [60, 0, -35], [90, 0, 60], [200, 0, 5]],
+    [[0, 50, 30], [100, 60, -25], [120, 50, 120], [200, 50, 5]],
+    [[0, 100, 0], [60, 120, 35], [90, 100, 60], [200, 100, 45]],
+    [[0, 150, 0], [60, 150, -35], [90, 180, 60], [200, 150, 45]]
+];
+
+g = bezier_surface(t_step, ctrl_pts);
+function_grapher(g, thickness);
+
+demo = "YES";
+// demo
+if(demo == "YES") {
+    width = 2;
+    r = 3;
+
+    pts = [
+        for(i = [0:len(ctrl_pts) - 1]) 
+            bezier_curve(t_step, ctrl_pts[i])
+    ]; 
+
+    // first bezier curve
+    for(i = [0:len(ctrl_pts) - 1]) {
+        color("green") union() {
+            for(j = [0:len(ctrl_pts[i]) - 1]) {
+                translate(ctrl_pts[i][j])
+                    sphere(r = r);
+            }
+
+            for(j = [0:len(ctrl_pts[i]) - 1]) {
+                hull_polyline3d( 
+                    ctrl_pts[i]
+                , width);
+            }            
+        }
+        
+        color("red") 
+            hull_polyline3d(
+                bezier_curve(t_step, ctrl_pts[i]), width
+            ); 
+    }
+
+    step = len(g[0]);
+    echo(step); 
+
+    // second bezier curve
+    ctrl_pts2 = [for(i = [0:len(pts) - 1]) pts[i][$t * step]];
+    color("blue") union() {
+        for(pt = ctrl_pts2) {
+            translate(pt) 
+                sphere(r = r);
+        }    
+        hull_polyline3d(ctrl_pts2, width);
+    }
+
+    color("black") 
+        hull_polyline3d(g[$t * step], width);    
+}