How to calculate an angle between 2 points..

[Chaosg1]

Ok I just want to know how to calculate an angle between two points, I think i should trignometric right? But how Could I calculate the angle let's say in this picture:

http://www.academiarpg.com/personal/dam ... s/img1.gif[/IMG]

This is what I did:

if @point_right.y > @point_left.y
        @oox = @point_right.x
        @ooy = @point_left.y
        @oposite = Math.sqrt(((@oox - @point_right.x)**2)+((@ooy - @point_right.y)**2))
        @adjacent = Math.sqrt((@oox - @point_left.x)**2) + ((@ooy - @point_left.y**2))
        @hypn = Math.sqrt(((@point_left.x - @point_right.x)**2)+((@point_left.y - @point_right.y)**2))
        @sene = @oposite / @hypn
        $game_player.angle = Math.cosh(@sene)
     elsif @point_right.y < @point_left.y
        @oox = @point_left.x
        @ooy = @point_right.y
        @oposite = Math.sqrt(((@oox - @point_left.x)**2)+((@ooy - @point_left.y)**2))
        @adjacent = Math.sqrt((@oox - @point_right.x)**2) + ((@ooy - @point_right.y**2))
        @hypn = Math.sqrt(((@point_left.x - @point_right.x)**2)+((@point_left.y - @point_right.y)**2))
        @sene = @oposite / @hypn
        $game_player.angle = Math.cosh(@sene)
      else
        @angle = 0
      end

note: my trignometric is a bit rusty....lol

Thanx for your help!

 

[~Atlaswing~]

Okay, you first have to determine at least 2 side lengths.. For example, the altitude(vertical) is 5 tiles(5units), then the base(horizontal) is 10 tiles(10units). You dont have to calculate for the hypotenuse but use TANGENT...

Like:
x = angle

tan x = 5/10
tan x = 1/2
x = arctan(1/20

*where arctan is tan with a -1 exponent(inverse)

x will be the angle...(use a calculator of course)

 

[SephirothSpawn]

Soh Cah Toa

sin = opp / hyp
cos = adj / hyp
tan = opp / adj

Meaning, if you have a side of a right triangle and and angle, you can figure out everything else.

So lets take a look at seph's crappy drawing

       A
  ----------
   \ a     |
    \      |
     \     |
     C\    |B
       \   |
        \  |
         \b|
          \|

However, since you (If I am right) are rotating a sprite. Right?

If you are wanting to rotate it from the center point, I could work out a method to offset the x and y for you.

 

[arev]

I always make it like this:

Math.atan2((y1 - y2), (x1 - x2)) * 180 / Math::PI

 

[Trickster]

I'll throw some code at you (but you have to figure out how to use it, but it does answer your question)

    if @distance_x == 0
      # The Angle is sign(distance_y) * - π / 2 (90° or 270°)
      @angle = @distance_y.sign * Math::PI / 2
    # If Y distance is 0 (Prevent Incorrect Direction for later)
    elsif @distance_y == 0
      # The Angle is sign(distance_x) - 1 * π / 2 (0° or 180°)
      @angle = (@distance_x.sign - 1) * Math::PI / 2
    else
      # The Angle is the Arctangent of @distance_y / @distance_x (slope)
      # Returns [-Ï€,Ï€]
      @angle = Math.atan2(@distance_y, @distance_x.to_f)
    end
    # Convert the angle to degrees
    @angle *= 180 / Math::PI

class Numeric
  def sign
    return 0 if self == 0 or self == 0.0
    return (self / self.abs).to_i
  end
end

 

[Chaosg1]

@seph that's right it's for rotating a sprite...If you fell like doing the method, thanx.
@Trickster : I am trying to decifre that code.. But I must say that its a bit complicate...
@all_others: thanx for your help...

 

[Trickster]

Perhaps you want the whole method I took that from, I'll leave the comments in also (My battle systems movement routine)

#--------------------------------------------------------------------------
  # * Move the sprite
  #   x     : x coordinate of the destination point
  #   y     : y coordinate of the destination point
  #   speed : Speed of movement (0 = delayed, 1+ = faster)
  #   delay : Movement delay if speed is at 0
  #--------------------------------------------------------------------------
  def move(x, y, speed = 1, delay = 0)
    # Set Destination Points speed and delay and move count set moving flag
    @destination_x = x
    @destination_y = y
    @move_speed = speed
    @move_delay = delay
    @move_old = @count
    @moving = true
    # Get the distance + (negative if to left or up positive if down or right)
    @distance_x = (@destination_x - self.x).to_f
    @distance_y = (@destination_y - self.y).to_f
    # Get slant distance (hypotenuse of the triangle (xf,yi) (xi,yf) and (xf,yf))
    @distance = Math.sqrt(@distance_x ** 2 + @distance_y ** 2)
    # Calculate angle of movement which is later used to determine direction
    # If X distance is 0 (Prevent Infinity Error)
    if @distance_x == 0
      # The Angle is sign(distance_y) * - π / 2 (90° or 270°)
      @angle = @distance_y.sign * Math::PI / 2
    # If Y distance is 0 (Prevent Incorrect Direction for later)
    elsif @distance_y == 0
      # The Angle is sign(distance_x) - 1 * π / 2 (0° or 180°)
      @angle = (@distance_x.sign - 1) * Math::PI / 2
    else
      # The Angle is the Arctangent of @distance_y / @distance_x (slope)
      # Returns [-Ï€,Ï€]
      @angle = Math.atan2(@distance_y, @distance_x.to_f)
    end
    # Convert the angle to degrees
    @angle *= 180 / Math::PI
  end

 

[GreatSuperheroPikachu]

what are those pis and squareroots for?

 

[Chaosg1]

To detect the angle, perhaps? Lol

 

[Trickster]

Well the PIs are for eating, but I never heard of a square root :P

But really here is a Full Explaination aside from the commented lines which explains that code

First I got the X Distance, and the Y Distance which represent the two shorter sides of the triangle, the longest side (the hypotenuse of the triangle) can be gotten by the Pythagorean identity SQRT(side1^2 + side2^2) = hypotenuse, so now I have all three sides so now to get the angle I can either do one of the four

Math.asin(ydistance / hypotenuse)
Math.acos(xdistance / hypotenuse)
Math.atan(ydistance / xdistance)
Math.atan2(ydistance, xdistance)

but noting the range of what each of these returns I choose Math.atan2

If X Distance is 0 then the angle is shooting straight up is the angle is PI / 2 or 3 * PI / 2 (To prevent Infinity Errors the script checks for this)

If Y Distance is 0 then the angle is flat so the angle is PI or 0

the angle is in radians so to convert to degrees you multiply by 180 / Pi

Trigonometry is fun

and I added a sign method to the Numeric class which gets the sign (returns 1 if postive -1 if negative and 0 if zero) and basically Its just the number divided by the Absolute value of that number

 

[~Atlaswing~]

Can't wait for trickster's BS!!!