World: r3wp
[Rebol School] Rebol School
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| Geomol 8-Feb-2009 [1862] | Taking some time to read and understand the chapter, I would guess, it wouldn't be too hard to construct an algorithm, that did the job. |
| kib2 8-Feb-2009 [1863] | Geomol: interesting.... |
| Steeve 8-Feb-2009 [1864] | what i don't understand, is your need to fulfill intersection points to postcript format, can't you send just an image of your drawnings ? |
| Geomol 8-Feb-2009 [1865] | Just realized, David H. Eberly is also the author of a book called "3D Game Engine Design". I should get this. |
| Anton 8-Feb-2009 [1866] | Just googling, this page seems to have good methods in it: http://www.groupsrv.com/computers/about179364.html |
| Geomol 8-Feb-2009 [1867] | Game developers have solved many such problems, and often in efficient ways (games like performance). Intersections with Bezier curves are discussed here: http://www.gamedev.net/community/forums/topic.asp?topic_id=385751 |
| kib2 8-Feb-2009 [1868] | Steeve : the purpose is to create a geometrical drawing dialect. Maybe I'll have a line (AB) that intersects an ellipsis and I wanted to use the intersection points |
| Steeve 8-Feb-2009 [1869] | with Rebol ? |
| Anton 8-Feb-2009 [1870] | *ding! did you mean Ellipse ? |
| kib2 8-Feb-2009 [1871x2] | Anton: yes, sorry :) |
Steeve: why not ? | |
| Anton 8-Feb-2009 [1873] | Why didn't you say so ? :) |
| Geomol 8-Feb-2009 [1874] | lol |
| Anton 8-Feb-2009 [1875] | .. because this is where I step in: http://anton.wildit.net.au/rebol/gfx/demo-intersection-points-of-line-and-ellipse.r http://anton.wildit.net.au/rebol/gfx/demo-intersection-points-of-line-and-circle.r |
| Steeve 8-Feb-2009 [1876] | Kib as i stated previously, if you don't need of the exact coordinates then you should use boolean operators of the graphic engine to find the intersection points (using colors clash), no need of math operations in that case. |
| Geomol 8-Feb-2009 [1877x2] | LOL again! I was just about to say: ah, intersection of a line and an ellipse, then you just have to go to Anton's library. |
Anton, that's a really cool demo with the line and ellipse! | |
| Anton 8-Feb-2009 [1879] | Thanks, have you not already seen it, though ? |
| Geomol 8-Feb-2009 [1880x2] | I think, I saw it the first time. It's just really cool! :-) |
And I can move the ellipse and endpoints of line around. Cool! | |
| Anton 8-Feb-2009 [1882] | Note: I did not solve the "nearest point on an ellipse to a given point" problem yet, which is hard, so the auto-selection of nearest control point is not perfect. |
| kib2 8-Feb-2009 [1883] | Anton: very nice ! bravo. |
| Anton 8-Feb-2009 [1884] | Thanks - I hope it's useful. |
| Geomol 8-Feb-2009 [1885] | About intersect of line and polynomial curve. There's a preview of the book, I was talking about here: http://books.google.com/books?id=82kntxqd1BoC&printsec=frontcover&dq=Geometric+Tools+for+Computer+Graphics#PPA250,M1 |
| kib2 8-Feb-2009 [1886] | Geomol: thanks |
| Geomol 8-Feb-2009 [1887] | The author, David Eberly, also has a lot of online documentation: http://www.geometrictools.com/Documentation/Documentation.html Look under "Intersection". |
| kib2 8-Feb-2009 [1888x2] | Geomol: nice, I've bookmarked ! |
Is there any string interpolation ? | |
| Geomol 8-Feb-2009 [1890x4] | You mean something like: >> rejoin ["Date: " now/date " Time: " now/time] == "Date: 8-Feb-2009 Time: 23:18:12" |
Some use COMPOSE, that will return a block: >> compose ["Date:" (now/date) "Time:" (now/time)] == ["Date:" 8-Feb-2009 "Time:" 23:21:57] That you can turn into a string with useful spaces by: >> form compose ["Date:" (now/date) "Time:" (now/time)] == "Date: 8-Feb-2009 Time: 23:21:08" | |
If you just wanna print the result, PRINT can work on a block, which will be reduced and spaces included in the output: >> print ["Date:" now/date "Time:" now/time] Date: 8-Feb-2009 Time: 23:24:27 | |
Another example: >> print ["2 + 2 =" 2 + 2] 2 + 2 = 4 | |
| kib2 8-Feb-2009 [1894x3] | Geomol: awesome, thanks ! (it's very useful for debugging) |
I just found an article on the subject I'm working on : http://www.alistapart.com/stories/simplecontentmanagement/ | |
I don't like the implementation, but the parse rules are worth reading | |
| Geomol 8-Feb-2009 [1897] | For debugging, you'll find PROBE to be very usefull. You can put it in about anywhere in your code, and it will just work as without PROBE. Examples: >> square-root probe 4 * 8 32 == 5.65685424949238 >> read probe join http:// "www.rebol.com" http://www.rebol.com connecting to: www.rebol.com == {<html> ... |
| kib2 8-Feb-2009 [1898] | nice, thanks. Now, I'm looking for something like hashtables (key-value). Is there something special, or do I need to use blocks ? |
| Geomol 8-Feb-2009 [1899x3] | >> if 1:00 > probe now/time [print "Go to bed!"] 0:05:35 Go to bed! |
Try >> ? hash | |
This will create a hashtable, that works like a block, but is faster: >> table: make hash! [a 1 b 12 c 4 d 65] | |
| kib2 8-Feb-2009 [1902x2] | Geomol: sorry, you can go to bed |
Geomol: and thanks a lot for your help | |
| Geomol 8-Feb-2009 [1904x2] | lol :-) it's ok, I'll go to bed in a moment. |
You can read a short intro to hash tables here: http://www.rebol.com/docs/core23/rebolcore-16.html#section-2.5 | |
| kib2 8-Feb-2009 [1906x4] | I just discovered this: |
markup: ["**" "strong" "//" "em" "__" "u" "--" "del" "^^" "sup" ".." "sub"] | |
foreach [bal html] markup [format text bal html] | |
where format is a function I've written. | |
| Geomol 8-Feb-2009 [1910] | REBOL has a build-markup function. |
| kib2 8-Feb-2009 [1911] | really ? |
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