Does the attached file look like a good implementation of my-point-at, or would it do things I wouldn’t expect for things not on the line between the two points, or ? I’m asking because I don’t think I completely understand point-at and what it does.
my-point-at.rkt
Description: Binary data
On Mar 15, 2015, at 6:29 PM, Alexander D. Knauth <alexan...@knauth.org> wrote: > Thanks! > > Actually, now that I think about it something like this would be really > helpful, and probably make more sense: > Maybe a version of point-at that would let you specify which pos’s should > match up where? > > (my-point-at v1 v2 v3 v4 #:normalize? #f) ; maps v1 to v3 and v2 to v4 > (my-point-at (pos 0 0 0) (pos 1 0 0) v1 v2 #:normalize? #f) ; maps the > origin to v1, and (pos 1 0 0) to v2. > (my-point-at (pos 0 0 0) (pos 0 0 1) v1 v2) ; equivalent to (point-at v1 v2) > (my-point-at v1 dv1 v2 dv2) ; equivalent to (my-point-at v1 (pos+ v1 dv1) > v2 (pos+ v2 dv2)) > > On Mar 15, 2015, at 5:58 PM, Neil Toronto <neil.toro...@gmail.com> wrote: > >> I'd generate a few different kinds of segments and then transform them into >> place. Don't use `rotate` for that, though - there's an easier way. >> >> Transforming a shape is pretty fast. Here's an insane example, using many >> more segments for a cylinder than you'd normally ever need: >> >> >> #lang racket >> >> (require pict3d) >> >> (define v1 (pos 1 1 1)) >> (define v2 (pos 2 3 2)) >> (define cyl >> (time >> (with-color (rgba "lightblue") >> ;; WOO 65536 TRIANGLES YEAH >> (move-z (cylinder origin (dir 1/4 1/4 1/2) #:segments 16384) >> 1/2)))) >> >> (define pict >> (time >> (combine (sphere v1 0.2) >> (sphere v2 0.2) >> (transform cyl (point-at v1 v2 #:normalize? #f))))) >> >> (time (pict3d->bitmap pict)) >> (time (pict3d->bitmap pict)) >> >> >> On my computer, creating `cyl` takes 5 seconds. Transforming it takes no >> measurable time. Rendering it the first time takes 1.5 seconds, and >> rendering it the second time takes 11 milliseconds. (Cylinders are frozen, >> so they'll always render faster the second time.) >> >> To stretch the cylinder between two points, the program >> >> 1. Creates the cylinder so that its bottom is at the origin and its >> top is at (pos 0 0 1). >> >> 2. Uses `point-at` without normalization to move the origin to `v1` and >> move (pos 0 0 1) to `v2`. >> >> Based on this and your other feedback, I think Pict3D needs >> >> * A `rotate-around` function that rotates a shape around a given point >> (with the default being the center of its bounding box). >> >> * A note in the docs for `rotate` et al that explain they rotate around >> the origin. >> >> * A "How Do I" section that includes things like the above example. >> >> * Notes in the docs about performance characteristics of different >> functions (e.g. that `cylinder` and `cone` return frozen Pict3Ds, and >> what that means you can expect from them). >> >> I expect performance characteristics to change, though, so that last one >> might be late coming. >> >> Neil ⊥ >> > > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users
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