[HELP] Circle to Line Collision

[Canned]

I know how to do rectangle collision, but how do I detect whether a circle has collided with a line?

[[Gandalf]]

I believe everything you need is included in the collision detection tutorial by richcash. Take a look on the second page for circle-line collisions.

[evildaddy911]

same problem man, i looked at the tutorial a week ago, and still havent figured out how to do it
im thinking that a good way would be to use the area/circumference formula, and whatdotcolor, but i havent figured out out to do the for loops for that

[Aange10]

evildaddy911 wrote:

idea im thinking that a good way would be to use the area/circumference formula, and whatdotcolor, but i haven't figured out out to do the for loops for that

Yes, there are many ways to do it (: ... For loops can be confusing at first, but once you lean them you'll find out how useful they are(:. But, anyways, I've taken a look at what you all want to do, and I've decided I'll help you all learn how to do it.

First and foremost, everything (other than the fors) I used came from http://compsci.ca/v3/viewtopic.php?t=13661&postdays=0&postorder=asc&start=0 (Collision detection tutorial). Sometimes it's easier, though, to learn when you already have a basic gist of things. Anyways, on to yall's problem:

Canned wrote:

I know how to do rectangle collision, but how do I detect whether a circle has collided with a line?

The same basic ideas. Lets look step-by-step at what to do. Now, the first thing to do (as always) is to define our variables. Here's my example I'll be using:

Turing:

View.Set ("graphics:maxx;maxy,position:center;center") % Set Screen % Define Variables var circle_radius, circle_x, circle_y : int var line_x1,line_x2,line_y1,line_y2 : int var circle_x_velocity : real := 3.0 circle_radius := 20 circle_x := 20 circle_y := maxy div 2 line_x1 := maxx - (maxx div 2) + 70 line_x2 := maxx - (maxx div 2) - 30 line_y1 := maxy div 2 line_y2 := maxy div 2 % An array so we can check the distance from each point in the line var distance : array 0 .. (line_x1 - line_x2) of real %%

Everything is pretty straight forward. We have variables to keep track of the points in the line, and the x,y & radius of the circle. Now, if you don't know what arrays are yet, I suggest you read http://compsci.ca/v3/viewtopic.php?t=14333, before you continue. ... The purpose of this array is so that we can find the distance from our circle to every point in the line (as apposed to just one point of the line).

Our next step is to put this array to use, using the equation given to us in the Collision Detection tutorial (the distance formula).

Turing:

% Moves the circle     circle_x += round (circle_x_velocity)     % Update the distance from the circle to each point of the line     for i : 0 .. upper (distance)         distance (i) := sqrt (((line_x1 - i) - circle_x) ** 2 + ((line_y1) - circle_y) ** 2)     end for

Now, the trick here is with the for statement. A for is just an infinite loop that repeats a number of times (x .. y) in this case, (0 .. upper(distance)), now if you read the arrays tutorial, you'll know that upper(distance) is just a pointer to the upper range of the array distance. Which in this case is (line_x1 - line_x2). So, to clarify, we have a for loop i that is repeating its self o .. upper(distance) times. In this situation, upper(distance) is = line_x1 - line_x2 which is = 100. So it's repeating itself 101 times (0 counts as a time!).
Each time a for executes its self, it assigns the number of executions to the variable i. So if it's on it's 20th execution, i = 19 (remember, 0 counts as an execution!). ... Now that we have a basic understanding of for loops (if you're still confused I suggest you read http://compsci.ca/v3/viewtopic.php?t=3678 as they can explain it better than I can), we can continue with the code:
As I said before, each time the for executes, it assigns i a value. Now by adding i into our distance equation, we effectively check every point on the line.

Turing:

% Draw our objects     drawline (line_x1, line_y1, line_x2, line_y2, red)     drawfilloval (circle_x, circle_y, circle_radius, circle_radius, blue)     % Check for collision at each point     for i : 0 .. upper (distance)         if distance (i) <= circle_radius then             put "Collision!"             exit         end if     end for

Now this piece of code should be a bit easier to understand. First we draw our circle and line. After we do that, we check to see if the distance between the circle's center and any of the points of the line are less than the circle's radius. If it is, we put "Collision!" at the top of our screen and exit the for.


At the end of the day, our code will look like this:

Turing:

View.Set ("graphics:maxx;maxy,position:center;center") % Set Screen % Define Variables var circle_radius, circle_x, circle_y : int var line_x1, line_x2, line_y1, line_y2 : int var circle_x_velocity : real := 3.0 circle_radius := 20 circle_x := 20 circle_y := maxy div 2 line_x1 := maxx - (maxx div 2) + 70 line_x2 := maxx - (maxx div 2) - 30 line_y1 := maxy div 2 line_y2 := maxy div 2 % An array so we can check the distance from each point in the line var distance : array 0 .. (line_x1 - line_x2) of real %% loop     cls     % Moves the circle     circle_x += round (circle_x_velocity)     % Update the distance from the circle to each point of the line     for i : 0 .. upper (distance)         distance (i) := sqrt (((line_x1 - i) - circle_x) ** 2 + ((line_y1) - circle_y) ** 2)     end for     % Draw our objects     drawline (line_x1, line_y1, line_x2, line_y2, red)     drawfilloval (circle_x, circle_y, circle_radius, circle_radius, blue)     % Check for collision at each point     for i : 0 .. upper (distance)         if distance (i) <= circle_radius then             put "Collision!"             exit         end if     end for     delay (50) end loop

If you didn't understand something, specify what you didn't understand and I'll try to explain it.

[evildaddy911]

i think i understand what i have to do, find the shortest distance between the circle and line, then determine if its less than the radius... but i still have no idea how the distance thing works.

what im doing with this is making a game, wasd moves the character, drawfilloval (myx, myy, 10, 10, red), clicking the mouse draws a line from (myx,myy) to (mousex,mousey). i want to find out if if this hits the enemy, drawfilloval (enemyx, enemyy, 10, 10, black). at the moment im using

code:

if whatdotcolor (enemyx, enemyy) = brightred then         cpuhp := cpuhp - 7500 end if

would it just be better to post my whole very sloppy code?

[Aange10]

If you post your code I can help you directly with your problem. If you've taken Geometry you'll know the distance formula is just an equation that gives you distance between two points. Now, if your wondering how the for loop works with the equation then that's another thing.

let me show you an example of how fors work.

Turing:

View.Set("text") for i : 1 .. 10     put "We have executed the for loop ", i," time(s)."     put " i is equal to:",i     put ""     delay (1000) end for

Now if you run this, you can see that i starts at the lower parameter (1) and ends at the upper parameter (10). The link i gave you on for loops earlier will explain this really well, and a bit more in depth.

Now, if you're wondering how this plays into our distance equation, lets take a look.

Turing:

for i : 0 .. upper (distance)         distance (i) := sqrt (((line_x1 - i) - circle_x) ** 2 + ((line_y1) - circle_y) ** 2)     end for

That is the same as saying

Turing:

distance (0) := sqrt (((line_x1 - 0) - circle_x) ** 2 + ((line_y1) - circle_y) ** 2) distance (1) := sqrt (((line_x1 - 1) - circle_x) ** 2 + ((line_y1) - circle_y) ** 2) distance (2) := sqrt (((line_x1 - 2) - circle_x) ** 2 + ((line_y1) - circle_y) ** 2) . . . distance (100) := sqrt (((line_x1 - 100) - circle_x) ** 2 + ((line_y1) - circle_y) ** 2)

But much shorter and efficient. Hopefully you understand now how that works. If you do, then continue on and let me explain the last part:

Turing:

% Check for collision at each point     for i : 0 .. upper (distance)         if distance (i) <= circle_radius then             put "Collision!"             exit         end if

We already defined the elements in distance (just did it in the first coding), so now we check to see if any of the distances are less than the radius of the circle. ... This is the same as writing

Turing:

if distance (0) <= circle_radius then             put "Collision!" end if if distance (1) <= circle_radius then             put "Collision!" end if if distance (2) <= circle_radius then             put "Collision!" end if if distance (3) <= circle_radius then             put "Collision!" end if . . . if distance (100) <= circle_radius then             put "Collision!" end if

Except that that would be nearly 300 lines of inefficient coding.

[evildaddy911]

so the distance array is flexible, containing the x,y for every pixel in the line,
then,
the first forloop checks the distance between each pixel and the circle center
the second checks if that distance is <= the radius

is that right?
also, since im not only using x values, should i make an array for the y values?

wait, doesnt Math.Distance do the same thing as

code:

distance (i) := sqrt (((line_x1 - i) - circle_x) ** 2 + ((line_y1) - circle_y) ** 2)

??

[Aange10]

evildaddy911 wrote:

so the distance array is flexible, containing the x,y for every pixel in the line,

You have the right idea, but technically no. The distance array isn't a flexible array (those are two different things) because the distance array has a cap as to how many elements are in the array. (In this situation the cap is whatever line_x1 - line_x2 equals).

Secondly, it doesn't contain the x,y for every pixel. The distance array contains the distance from the center of the circle to each x pixel of the line.

evildaddy911 wrote:

the first forloop checks the distance between each pixel and the circle center
the second checks if that distance is <= the radius

is that right?

Correct!

evildaddy911 wrote:

wait, doesnt Math.Distance do the same thing as
code:
distance (i) := sqrt (((line_x1 - i) - circle_x) ** 2 + ((line_y1) - circle_y) ** 2)
??

Essentially, but now that's no fun! (I personally never use it; I like to see where my numbers are coming from. Also, it takes longer for the computer to go find the function -> execute the function -> output the result than it does for it to just do the equation.)

[evildaddy911]

for now im going to stick to the Math.Distance,
thanks for the help!

[Aange10]

No problem!(: So I take it your program works now?

[evildaddy911]

not completely, i have to change half the code...

[Aange10]

evildaddy911 @ 16/10/2011, 2:01 pm wrote:

not completely, i have to change half the code...

Happens =/ ... If you need help feel free to ask


EDIT: Just realized

Aange10 wrote:

A for is just an infinite loop that repeats a number of times

... Oops. Sorry, i meant to say "A for is just a loop that repeats itself a number of times"

Sorry

[evildaddy911]

yah, im stuck
heres my code, im trying to replace the whatdotcolor for the brightgreen i shoot and the purple that the enemy shoots:

code:

View.Set ("graphics:max;max,nobuttonbar") var myx, myy, mousex, mousey, button, cpuhp, myhp, kills, damage, typ, rad, enemyx, enemyy, move, score, dlay : int var mode : string var chars : array char of boolean enemyx := Rand.Int (100, maxx - 100) enemyy := Rand.Int (100, maxy - 100) %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %                                                               DRAWENEMY proc drawenemy     drawfilloval (enemyx, enemyy, 10, 10, white)     move := Rand.Int (1, 8)     if enemyx > 0 then         if move = 1 then             enemyx := enemyx + Rand.Int (1, 6)         end if     end if     if enemyy > 0 then         if move = 2 then             enemyy := enemyy + Rand.Int (1, 6)         end if     end if     if enemyx < maxx then         if move = 3 then             enemyx := enemyx - Rand.Int (1, 6)         end if     end if     if enemyy < maxy then         if move = 4 then             enemyy := enemyy - Rand.Int (1, 6)         end if     end if     if enemyy < maxy then         if enemyx < maxx then             if move = 5 then                 enemyy := enemyy - Rand.Int (1, 6)                 enemyx := enemyx - Rand.Int (1, 6)             end if         end if     end if     if enemyy < maxy then         if enemyx > 0 then             if move = 6 then                 enemyx := enemyx + Rand.Int (1, 6)                 enemyy := enemyy - Rand.Int (1, 6)             end if         end if     end if     if enemyy > 0 then         if enemyx > 0 then             if move = 7 then                 enemyx := enemyx + Rand.Int (1, 6)                 enemyy := enemyy + Rand.Int (1, 6)             end if         end if     end if     if enemyy > 0 then         if enemyx < maxx then             if move = 8 then                 enemyx := enemyx - Rand.Int (1, 4)                 enemyy := enemyy + Rand.Int (1, 4)             end if         end if     end if     drawfilloval (enemyx, enemyy, 10, 10, black)     drawfilloval (enemyx - 2, enemyy, 1, 2, green)     drawfilloval (enemyx + 2, enemyy, 1, 2, green)     drawline (enemyx - 3, enemyy - 4, enemyx + 3, enemyy - 4, red) end drawenemy %                                                               HEALTH proc health     if whatdotcolor (enemyx, enemyy) = brightred then         cpuhp := cpuhp - 7500     end if     if whatdotcolor (enemyx, enemyy) = brightblue then         cpuhp := cpuhp - 125     end if     if whatdotcolor (enemyx, enemyy) = brightgreen then         cpuhp := cpuhp - 3     end if     if whatdotcolor (myx, myy) = purple then         myhp := myhp - 5     end if     if whatdotcolor (myx, myy) = gray then         myhp := myhp - 100     end if     if whatdotcolor (myx, myy) = brightblue then         myhp := myhp - 200     end if     put cpuhp     put myhp end health %                                                               DAMAGE proc dmge     for counter : 0 .. 100         if whatdotcolor (counter, 100) = brightred then             damage := damage + 125             score := score + 125         end if         if whatdotcolor (100, counter) = brightred then             damage := damage + 125             score := score + 125         end if         if whatdotcolor (counter, 100) = brightblue then             damage := damage + 2             score := score + 2         end if         if whatdotcolor (100, counter) = brightblue then             damage := damage + 2             score := score + 2         end if         if whatdotcolor (counter, 100) = brightgreen then             damage := damage + 1             score := score + 1         end if         if whatdotcolor (100, counter) = brightgreen then             damage := damage + 1             score := score + 1         end if     end for     if whatdotcolor (myx, myy) = purple then         damage := damage * (1 div 100)     end if     if whatdotcolor (myx, myy) = gray then         damage := damage - 300     end if     if whatdotcolor (myx, myy) = brightblue then         damage := damage - 750     end if     put damage end dmge %                                                               GRENADE proc grenade (l, m : int)     if mode = "KILLS" then         drawfilloval (Rand.Int (l - 50, l + 50), Rand.Int (m - 10, m + 10), 15, 15, brightblue)         health     elsif mode = "DAMAGE" then         drawfilloval (Rand.Int (l - 125, l + 125), Rand.Int (m - 10, m + 10), 15, 15, brightblue)         dmge     end if     delay (250)     cls end grenade %                                                               SHOT proc shot (q, w, e, r, clr : int)     drawline (q + 1, w, 1000 * (e - q) + e + 1, 1000 * (r - w) + r, clr)     drawline (q, w, 1000 * (e - q) + e, 1000 * (r - w) + r, clr)     drawline (q - 1, w, 1000 * (e - q) + e - 1, 1000 * (r - w) + r, clr)     drawline (q, w + 1, 1000 * (e - q) + e, 1000 * (r - w) + r + 1, clr)     drawline (q, w - 1, 1000 * (e - q) + e, 1000 * (r - w) + r - 1, clr)     if mode = "KILLS" then         health     elsif mode = "DAMAGE" then         dmge     end if     delay (10)     cls end shot %                                                               ATTK proc attk (a, b : int)     typ := Rand.Int (0, 5)     if typ < 3 then         if mode = "KILLS" then             for counter : 1 .. 100                 drawline (a, b, Rand.Int (0, maxx), Rand.Int (0, maxy), purple)             end for         elsif mode = "DAMAGE" then             for counter : 1 .. Rand.Int (500, 2000)                 drawline (a, b, 2 * Rand.Int (-5, maxx), 2 * Rand.Int (-5, maxy), purple)             end for         end if         health         delay (20)         cls     elsif typ = 3 then         myhp := myhp - 1         damage := damage - 100     elsif typ = 4 then         if mode = "DAMAGE" then             drawfilloval (a, b, maxy div 2, maxy div 2, gray)             dmge         end if         delay (20)         cls     elsif typ = 5 then         if mode = "DAMAGE" then             for qwe : 1 .. Rand.Int (15, 50)                 drawfilloval (Rand.Int (100, maxx), Rand.Int (100, maxy), 25, 25, brightblue)             end for         elsif mode = "KILLS" then             drawfilloval (Rand.Int (0, maxx), Rand.Int (0, maxy), 40, 40, brightblue)             health         end if         delay (10)         cls     end if end attk %                                                               BUTTONS proc buttons     %                                                           MOVEMENT     if myy < maxy then         if chars ('w') then             drawfilloval (myx, myy, 10, 10, white)             myy := myy + 5         end if     end if     if myx < maxx - 1 then         if chars ('d') then             drawfilloval (myx, myy, 10, 10, white)             myx := myx + 5         end if     end if     if myx > 0 then         if chars ('a') then             drawfilloval (myx, myy, 10, 10, white)             myx := myx - 5         end if     end if     if myy > 0 then         if chars ('s') then             drawfilloval (myx, myy, 10, 10, white)             myy := myy - 5         end if     end if     %                                                           ATTACKS     if chars (chr (ORD_SPACE)) then         grenade (mousex, mousey)     end if     if chars ('f') then         for i : 1 .. 25             drawoval (myx, myy, i, i, brightred)             delay (30)         end for         if mode = "KILLS" then             health         elsif mode = "DAMAGE" then             dmge         end if         cls     end if     if button = 1 then         shot (myx, myy, mousex, mousey, brightgreen)     end if end buttons %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% loop     loop         put "Welcome to my game."         put "The objective is to destroy the enemy using lasers, grenades and melee attacks." : 10         put ""         put "Use the arrow keys to move your character, a small red ball."         put "Click the mouse to shoot a laser, press Space to use a grenade, or press F to perform a melee attack."         put "Pressing M will end the game and P will pause."         put "WARNING: grenades will hurt you too"         put "The enemy will be a black square in the bottom corner. It will randomly shoot purple lasers across the screen, and will sometimes use a melee attack, in the form of a gray circle."         put "Type KILLS or DAMAGE to begin, or QUIT to quit"         get mode         exit when mode = "KILLS"         exit when mode = "DAMAGE"         if mode = "QUIT" then             Window.Close (defWinID)         end if         delay (250)         cls     end loop     myx := Rand.Int (maxy div 2, maxx)     myy := Rand.Int (maxy div 2, maxy)     cpuhp := 200     myhp := 500     kills := 0     damage := 100     score := 0     %%%%%%%%%%%%%%%%%%%%%%%%%%     if mode = "KILLS" then         %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%         loop             %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%             drawenemy         %%%%%draws enemy             Mouse.Where (mousex, mousey, button)             Input.KeyDown (chars)             exit when chars ('m')             for dly : 1 .. 20                 if dly = 1 then                     attk (enemyx, enemyy)                 end if             end for             %                                                       MOVEMENT             buttons             %                                                       PAUSE             if chars ('p') then                 loop                     Mouse.Where (mousex, mousey, button)                     drawfilloval (enemyx, enemyy, 10, 10, black)                     drawfilloval (enemyx - 2, enemyy, 1, 2, green)                     drawfilloval (enemyx + 2, enemyy, 1, 2, green)                     drawline (enemyx - 3, enemyy - 4, enemyx + 3, enemyy - 4, red)                     drawfilloval (myx, myy, 10, 10, red)                     put "GAME PAUSED"                     put "ENEMY:", cpuhp, "  YOU:", myhp, "  KILLS:", kills                     put "press L to resume"                     Input.KeyDown (chars)                     if chars ('l') then                         exit                     end if                     delay (250)                     cls                 end loop             end if             %                                                       KILLS             if cpuhp < 0 then                 put "KILL"                 kills := kills + 1                 cpuhp := 200 + 10 * kills                 myhp := myhp + 2 * kills                 enemyx := Rand.Int (100, maxx - 100)                 enemyy := Rand.Int (100, maxy - 100)                 delay (1000)             end if             exit when myhp < 0             drawfilloval (myx, myy, 10, 10, red)             delay (20)         end loop     end if     %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%     if mode = "DAMAGE" then         %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%         loop             %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%             drawfillbox (0, 0, 100, 100, black)             %%%%%draws enemy             Mouse.Where (mousex, mousey, button)             Input.KeyDown (chars)             exit when chars ('m')             dlay := Rand.Int (1, 10)             if dlay = 1 then                 attk (50, 50)             end if             %                                                   MOVEMENT             buttons             %                                                   PAUSE             if chars ('p') then                 loop                     drawfillbox (0, 0, 100, 100, black)                     put "GAME PAUSED"                     put "DAMAGE:", damage                     put "press L to resume"                     Input.KeyDown (chars)                     if chars ('l') then                         exit                     end if                     delay (250)                     cls                 end loop             end if             exit when damage < 0             drawfilloval (myx, myy, 10, 10, red)             delay (20)         end loop     end if     put "GAME OVER. Restart game"     if mode = "KILLS" then         put "KILLS:", kills     elsif mode = "DAMAGE" then         put "SCORE:", score     end if     delay (100)     put ""     put "" end loop

can you help?

[Aange10]

I'm sure I can. But first you need to clean up a bit. 1. You need to do more commenting on your code. For example, what is the purpose of each line. When you finish commenting that, not only can other people fully understand it, but you might figure out what's wrong as well.
2. typ,rad,dly ... What do these variables mean?

and 3. I suggest you make some variables like

Turing:

var player_laser, player_gernade, player_mele, cpu_laser : int player_laser := brightred . .

That away it'll be easier to see what the whatdot colors are looking for. Instead of seeing "brightpurple" everywhere, we could see "enemy laser"

[evildaddy911]

ok... ill work on it