canvas - How find if a point is in a wedge of a other point javascript -


i have canvas , draw 2 points. have draw 2 straight lines each point. must check whether point u sees point v , vice versa.

to know, necessary see if point v in wedge of point u , vice versa:

-here v wedge of u, v sees u u don't see v

-here v sees u , u sees v

if 2 points in wedge of each 1 segment drawn between 2 points.

how can kind of wedge in canvas javascript?

cross product of 2 vectors.

using cross product of line (x1,y1, x2,y2) ax vector (x2-x1, y2-y1) , vector line start point x,y (x - x1, y - y1) give number negative if point left of line, 0 if point along line, , positive if point right of line.

thus point in view of v has to right of v's left arm , left of v's right arm.

a v described follows

const v = {     lx : ?,  // point on left v     ly : ?,      x : ?,  // point of v     y : ?,     rx : ?,     ry : ?, }

the following function return true if v1 can see v2 v1 , v2 objects described above.

function cansee(v1,v2){     const lx = v1.lx - v1.x;  // vector center left line end     const ly = v1.ly - v1.y;     const cx = v2.x  - v1.x;  // vector center v2's center     const cy = v2.y  - v1.y;     const rx = v1.rx - v1.x;  // vector center right line end     const ry = v1.ry - v1.y;      // cross product of left , right arms other v's center     const lc = lx * cy - ly * cx;     const rc = rx * cy - ry * cx;      return (lc > 0 && rc < 0);  // return true if v2 center right of                                 // left arm , left of arm.                                 // else return false; }

using function can find out if both can see each other follows.

if(cansee(v1, v2) && cansee(v2, v1)){ } // both can see each other else { } //one or none can see other

it important points on correct sides. left , right defined when standing @ line start , looking towards line end


Comments

Post a Comment

Popular posts from this blog

android - InAppBilling registering BroadcastReceiver in AndroidManifest -

i'm implementing inapp billing in android app. works well, however, i'm trying decouple broadcast receiver activity manifest. suggestion in android's trivialdrive sample: // important: dynamically register broadcast messages updated purchases. // register receiver here instead of <receiver> in manifest // because call getpurchases() @ startup, therefore can ignore // broadcasts sent while app isn't running. // note: registering listener in activity bad idea, done here // because sample. regardless, receiver must registered after // iabhelper setup, before first call getpurchases(). currently there's class extends broadcastreceiver : public class iabbroadcastreceiver extends broadcastreceiver { /** * intent action receiver should filter for. */ public static final string action = "com.android.vending.billing.purchases_updated"; private final iabbroadcastlistener mlistener; public iabbroadcastreceiver(iabbroadcastlistener listener) { m...
Read more

python Tkinter Capturing keyboard events save as one single string -

is possible store keyboard events 1 string? code below stores 1 char , prints it. card reader or bar code reader, contains collection of character/ string not 1 character @ time. goal save char pressed text variable. from tkinter import * root = tk() def key(event): text= event.char text+= event.char print ("pressed", text) def callback(event): frame.focus_set() print ("clicked at", event.x, event.y) frame = frame(root, width=100, height=100) frame.bind("<key>", key) frame.bind("<button-1>", callback) frame.pack() root.mainloop() currently, creating text variable , everytime key() function gets called, , text stores last character typed. you can define text module level variable , , use module level text inside key function - text = '' def key(event): global text text+= event.char print("pressed", text)
Read more

sql server - Why does Linq-to-SQL add unnecessary COUNT()? -

here tables: create table customer ( cid int primary key, name varchar(32) ) create table ord ( oid int primary key, cid int foreign key references customer, address varchar(20) ) here's linq-to-sql statement: var aaa = c in db.customer select new { c, o = c.ord.tolist() }; and here's inexplicable query generated linq-to-sql: select [t0].[cid] [cid], [t0].[name] [name], [t1].[oid] [oid], [t1].[cid] [cid2], [t1].[address] [address], (select count(*) [dbo].[ord] [t2] [t2].[cid] = [t0].[cid]) [value] [dbo].[customer] [t0] left outer join [dbo].[ord] [t1] on [t1].[cid] = [t0].[cid] order [t0].[cid], [t1].[oid] i want understand how rid of count(*) part. it's entirely uncalled for! linq needs count(*) in order determine number of entries returned o = c.ord.tolist() .
Read more