diff --git a/attachments.scad b/attachments.scad index 846ed0e..fad8606 100644 --- a/attachments.scad +++ b/attachments.scad @@ -385,6 +385,78 @@ _ANCHOR_TYPES = ["intersect","hull"]; // _show_corners(_corners("ALL",[FRONT+RIGHT+TOP,FRONT+LEFT+BOT]), // toplabel=["except=[FRONT+RIGHT+TOP,"," FRONT+LEFT+BOT]"]); // } +// Subsection: Anchoring of Non-Rectangular Objects and Anchor Type (atype) +// We focused above on rectangular objects that have well-defined faces and edges aligned with the coordinate axes. +// Things get difficult when the objects are curved, or even when their edges are not neatly aligned with the coordinae axes. +// In these cases, the library may provide multiple different anchoring schemes, called the anchor types. When a module supports +// multiple anchor types, use the `atype=` parameter to select the anchor type you need. +// . +// First consider the case of a simple rectangle whose corners have been rounded. Where should the anchors lie? +// The default anchor type puts them in the same location as the anchors of an unrounded rectangle, which means that for +// positive rounding radii, they are not even located on the perimeter of the object. +// Figure(2D,Med): Default "box" atype anchors for a rounded {{rect()}} +// rect([100,50], rounding=[10,0,0,-20],chamfer=[0,10,-20,0]) show_anchors(); +// Continues: +// This choice enables you to position the box, or attach things to it, without regard to its rounding or chamfers. If you need to +// anchor onto the roundovers or chamfers then you can use the "perim" anchor type: +// Figure(2D,Med): The "perim" atype for a rounded and chamfered {{rect()}} +// rect([100,50], rounding=[10,0,0,-20],chamfer=[0,10,-20,0],atype="perim") show_anchors(); +// Continues: +// With this anchor type, the anchors are located on the perimeter. For positive roundings they point in the standard anchor direction; +// for negative roundings they are parellel to the base. As noted above, for circles, cylinders, and spheres, the anchor point is +// determined by choosing the point where the anchor vector intersects the shape. On a circle, this results in an anchor whose direction +// matches the user provided anchor vector. But on an ellipse, something else happens: +// Figure: Anchors on an ellipse. The red arrow shows a TOP+RIGHT anchor direction. +// ellipse([70,30]) show_anchors(); +// stroke([[0,0],[45,45]], color="red",endcap2="arrow2"); +// Continues: +// For a TOP+RIGHT anchor direction, the surface normal at the intersection point does not match the anchor direction, +// so the direction of the anchor shown in blue does not match the direction specified, in red. +// Anchors computed this way have anchor type "intersect". When a shape is concave, intersection anchors can produce +// a result buried inside the shape's concavity. Consider the RIGHT anchor of this supershape example: +// Figure: A supershape with "intersect" anchor type: +// supershape(n=150,r=75, m1=4, n1=4.0,n2=16, n3=1.5, a=0.9, b=9,atype="intersect") show_anchors(); +// Continues: +// A different anchor type called "hull" finds anchors that are on the convex hull of the shape. +// Figure: A supershape with "hull" anchor type: +// supershape(n=150,r=55, m1=4, n1=4.0,n2=16, n3=1.5, a=0.9, b=9,atype="hull") show_anchors(); +// Continues: +// Hull anchoring works by creating the line (or plane in 3D) that is normal to the specified anchor direction, and +// finding the point farthest from the center that intersects that line (or plane). +// Figure: Finding the RIGHT and BACK+LEFT "hull" anchors +// supershape(n=128,r=55, m1=4, n1=4.0,n2=16, n3=1.5, a=0.9, b=9,atype="hull") { +// position(RIGHT) color_this("red")rect([1,90],anchor=LEFT); +// attach(RIGHT)anchor_arrow2d(13); +// attach(BACK+LEFT) { +// anchor_arrow2d(13); +// color_this("red")rect([30,1]); +// } +// } +// Continues: +// In the example the RIGHT anchor is found when the normal line (shown in red) is tangent to the shape at two points. +// The anchor is then taken to be the midpoint. The BACK+LEFT anchor occurs with a single tangent point, and the +// anchor point is located at the tangent point. For circles intersection is done to the exact circle, but for other +// shapes these calculations are done on the point lists that defines the shape, so if you change the number of points +// in the list, the precise location of the anchors can change. You can also get surprising results if your point list is badly chosen. +// Figure: Circle anchor in blue. The red anchor is computed to a point list of a circle with 17 segments. +// circle(r=31,$fn=128) attach(TOP)anchor_arrow2d(15); +// region(circle(r=33,$fn=17)) {color("red")attach(TOP)anchor_arrow2d(13);} +// Continues: +// The figure shows a large horizontal offset due to a poor choice of sampling for the circular shape when using the "hull" anchor type. +// The determination of "hull" or "intersect" anchors may depend on the location of the centerpoint used in the computation. +// Some of the modules allow you to change the centerpoint using a `cp=` argument. If you need to change the centerpoint for +// a module that does not provide this option, you can use the generic {{region()}} module, which will let you specify a centerpoint. +// The default center point is the centroid, specified by "centroid". You can also choose "mean", which gives the mean of all +// the data points, or "bbox", which gives the centerpoint of the bounding box for the data. Your last option for centerpoint is to +// choose an arbitrary point that meets your needs. +// Figure: The centerpoint for "intersect" anchors is located at the red dot +// region(supershape(n=128,r=55, m1=4, n1=4.0,n2=16, n3=1.5, a=0.9, b=9),atype="intersect",cp=[0,30]) show_anchors(); +// color("red")back(30)circle(r=2,$fn=16); +// Continues: +// Note that all the anchors for an object have to be determined based on one anchor type and relative to the same centerpoint. +// The supported anchor types for each module appear in the "Anchor Types" section of its entry. + + @@ -2033,7 +2105,7 @@ function reorient( !is_undef(path)? [path] : undef ) - (anchor==CENTER && spin==0 && orient==UP && p!=undef)? p : +// (anchor==CENTER && spin==0 && orient==UP && p!=undef)? p : let( geom = is_def(geom)? geom : attach_geom(