More tutorial editing.

tutorials/Basic_Shapes.md

@@ -1,12 +1,14 @@
 # Basic Shapes Tutorial
 
-## Enhanced Primitives
+## Primitives
-There are 5 built-in primitive shapes that OpenSCAD provides.  `square()`, `circle()`, `cube()`, `cylinder()`, and `sphere()`.
+There are 5 built-in primitive shapes that OpenSCAD provides.
-The BOSL2 library extends or provides alternative to these shapes so that they support more features, and more
+`square()`, `circle()`, `cube()`, `cylinder()`, and `sphere()`.
-ways to simply reorient them.
+The BOSL2 library extends or provides alternative to these shapes so
+that they support more features, and more ways to simply reorient them.
 
-### 2D Square
+### 2D Squares
 You still use `square()` in the familiar ways that OpenSCAD provides:
+
 ```openscad-example
     square(100, center=false);
 ```
@@ -19,60 +21,75 @@ You still use `square()` in the familiar ways that OpenSCAD provides:
     square([60,40], center=true);
 ```
 
-### rect()
+BOSL2 has a `rect()` command that acts an an enhanced `square()` that has
-BOSL2 has a `rect()` command that acts an an enhanced `square()` that has extended functionality. For example, it allows you to round the corners:
+extended functionality. For example, it allows you to round the corners:
+
 ```openscad-example
     rect([60,40], center=true, rounding=10);
 ```
 
 It also supports chamfers:
+
 ```openscad-example
     rect([60,40], center=true, chamfer=10);
 ```
 
 It allows you to specify *which* corners get rounded or chamferred:
+
 ```openscad-example
     rect([60,40], center=true, rounding=[0,5,10,15]);
 ```
+
 ```openscad-example
     rect([60,40], center=true, chamfer=[0,5,10,15]);
 ```
 
 It will even let you mix rounding and chamferring:
+
 ```openscad-example
     rect([60,40], center=true, rounding=[5,0,10,0], chamfer=[0,5,0,15]);
 ```
 
 ### Anchors and Spin
-
+Another way that `rect()` is enhanced over `square()`, is that you can anchor,
+spin and attach it.
 The `anchor=` argument is an alternative to `center=`, which allows more
 alignment options.  It takes a vector as a value, pointing roughly towards
 the side or corner you want to align to the origin.  For example, to align
 the center of the back edge to the origin, set the anchor to `[0,1]`:
+
 ```openscad-example
     rect([60,40], anchor=[0,1]);
 ```
 
 To align the front right corner to the origin:
+
 ```openscad-example
     rect([60,40], anchor=[1,-1]);
 ```
 
 To center:
+
 ```openscad-example
     rect([60,40], anchor=[0,0]);
 ```
 
-To make it clearer when giving vectors, there are several standard vector constants defined:
+To make it clearer when giving vectors, there are several standard vector
-- `LEFT` is a vector towards X-.  (`[-1,0,0]`)
+constants defined:
-- `RIGHT` is a vector towards X+.  (`[1,0,0]`)
+
-- `FRONT`, `FORWARD` or `FWD` is a vector towards Y-.  (`[0,-1,0]`)
+Constant | Direction | Value
-- `BACK` is a vector towards Y+.  (`[0,1,0]`)
+-------- | --------- | -----------
-- `BOTTOM`, `BOT`, `BTM`  or `DOWN` is a vector towards Z-.  (`[0,0,-1]`)  Not used with 2D anchors.
+`LEFT`   | X-        | `[-1,0,0]`
-- `TOP`, or `UP` is a vector towards Z+.  (`[0,0,1]`)  Not used with 2D anchors.
+`RIGHT`  | X+        | `[1,0,0]`
-- `CENTER` or `CTR` is a centered vector. (`[0,0,0]`)
+`FRONT`/`FORWARD`/`FWD` | Y- | `[0,-1,0]`
+`BACK`   | Y+        | `[0,1,0]`
+`BOTTOM`/`BOT`/`BTM`/`DOWN` | Z- | `[0,0,-1]` (3D only.)
+`TOP`/`UP` | Z+      | `[0,0,1]` (3D only.)
+`CENTER`/`CTR` | Centered | `[0,0,0]`
+
+Note that even though these are 3D vectors, you can use most of them,
+(except `UP`/`DOWN`, of course) for anchors in 2D shapes:
 
-Note that even though these are 3D vectors, you can use most of them, (except `UP`/`DOWN`, of course) for anchors in 2D shapes:
 ```openscad-example
     rect([60,40], anchor=BACK);
 ```
@@ -82,22 +99,27 @@ Note that even though these are 3D vectors, you can use most of them, (except `U
 ```
 
 You can add them together to point to corners:
+
 ```openscad-example
     rect([60,40], anchor=FRONT+RIGHT);
 ```
 
-Finally, the `spin` argument can rotate the shape by a given number of degrees clockwise:
+Finally, the `spin` argument can rotate the shape by a given number of degrees
+clockwise:
+
 ```openscad-example
     rect([60,40], anchor=CENTER, spin=30);
 ```
 
 Anchoring or centering is performed before the spin:
+
 ```openscad-example
     rect([60,40], anchor=BACK, spin=30);
 ```
 
 ### Enhanced 2D Circle
 The enhanced `circle()` primitive can be used like the OpenSCAD built-in:
+
 ```openscad-example
     circle(r=50);
 ```
@@ -112,14 +134,18 @@ Since a circle in OpenSCAD can only be approximated by a regular polygon with
 a number of straight sides, this can lead to size and shape inaccuracies.  To
 counter this, the `realign` and `circum` arguments are also provided.
 
-The `realign` argument, if set `true`, rotates the circle by half the angle between sides:
+The `realign` argument, if set `true`, rotates the circle by half the angle
+between sides:
+
 ```openscad-example
     circle(d=100, $fn=8, realign=true);
 ```
 
-The `circum` argument, if true, makes the polygon describing the circle circumscribe the ideal circle instead of inscribing it.
+The `circum` argument, if true, makes the polygon describing the circle
+circumscribe the ideal circle instead of inscribing it.
 
 Inscribing the ideal circle:
+
 ```openscad-example
     difference() {
         circle(d=100, $fn=360);
@@ -128,6 +154,7 @@ Inscribing the ideal circle:
 ```
 
 Circumscribing the ideal circle:
+
 ```openscad-example
     difference() {
         circle(d=100, $fn=6, circum=true);
@@ -136,6 +163,7 @@ Circumscribing the ideal circle:
 ```
 
 You can also use anchor and spin on enhanced `circle()`:
+
 ```openscad-example
     circle(r=50, anchor=BACK);
 ```
@@ -144,36 +172,45 @@ You can also use anchor and spin on enhanced `circle()`:
     circle(r=50, anchor=FRONT+RIGHT);
 ```
 
-Using spin on a circle may not make initial sense, until you remember that anchoring is performed before spin:
+Using spin on a circle may not make initial sense, until you remember that
+anchoring is performed before spin:
+
 ```openscad-example
     circle(r=50, anchor=FRONT, spin=30);
 ```
 
-### Echanced 3D Cube
+### Enhanced 3D Cube
 You can use enhanced `cube()` like the normal OpenSCAD built-in:
+
 ```openscad-example
     cube(100);
 ```
+
 ```openscad-example
     cube(100, center=true);
 ```
+
 ```openscad-example
     cube([50,40,20], center=true);
 ```
 
 You can use `anchor` similarly to `square()`, except you can anchor vertically
 too, in 3D, allowing anchoring to faces, edges, and corners:
+
 ```openscad-example
     cube([50,40,20], anchor=BOTTOM);
 ```
+
 ```openscad-example
     cube([50,40,20], anchor=TOP+BACK);
 ```
+
 ```openscad-example
     cube([50,40,20], anchor=TOP+FRONT+LEFT);
 ```
 
 You can use `spin` as well, to rotate around the Z axis:
+
 ```openscad-example
     cube([50,40,20], anchor=FRONT, spin=30);
 ```
@@ -181,33 +218,40 @@ You can use `spin` as well, to rotate around the Z axis:
 3D objects also gain the ability to use an extra trick with `spin`;
 if you pass a list of `[X,Y,Z]` rotation angles to `spin`, it will
 rotate by the three given axis angles, similar to using `rotate()`:
+
 ```openscad-example
     cube([50,40,20], anchor=FRONT, spin=[15,0,30]);
 ```
 
 3D objects also can be given an `orient` argument that is given as a vector,
 pointing towards where the top of the shape should be rotated towards.
+
 ```openscad-example
     cube([50,40,20], orient=UP+BACK+RIGHT);
 ```
 
 If you use `anchor`, `spin`, and `orient` together, the anchor is performed
 first, then the spin, then the orient:
+
 ```openscad-example
     cube([50,40,20], anchor=FRONT, spin=45, orient=UP+FWD+RIGHT);
 ```
 
-### Echanced 3D Cylinder
+### Enhanced 3D Cylinder
 You can use the enhanced `cylinder()` as normal for OpenSCAD:
+
 ```openscad-example
     cylinder(r=50,h=50);
 ```
+
 ```openscad-example
     cylinder(r=50,h=50,center=true);
 ```
+
 ```openscad-example
     cylinder(d=100,h=50,center=true);
 ```
+
 ```openscad-example
     cylinder(d1=100,d2=80,h=50,center=true);
 ```