Object Avoidance newbie question

[metal Slug 2]

What is it you are trying to achieve?
Hi, I am a first year programmer (ISC3U), so please bear with me. I've gone a little ahead and started playing with graphics in Turing. What I have done so far is created a program which (based on the Turing walk-through on this site, Thanks! =) ) creates two circles. One circle (the red one), you control with the D-pad on your keyboard. The other ball (the Blue one), moves in the opposite direction you are in, if you are also within an X distance from it. This will eventually be part of my final project (A Zelda RPG...FTW!)..as some sort of enemy maneuvering.

What is the problem you are having?
I would like to know how I can make the blue ball travel linearly in the opposite direction of the red ball based upon the slope between the red and blue ball. Essentially, if I am traveling diagonally right and up at the blue ball, I want the blue ball to travel right and up also, away from the ball I'm controlling...or have the ball move away at the same angle in which I am approaching it
I am also having problems with flickering, I cannot figure out how to get it to work...View.Update and "offscreenonly" do not work for me...
[EDIT] : i have solved the flickering problem. apparently, "View.Update" needs to be pasted AFTER any visual changes are made...which makes so much sense...

Describe what you have tried to solve this problem
<I have tried what I described in the first paragraph. I tried plugging the blue balls x and y coordinates into y = mx + b, by incrementing the x-value of the blue ball by <any value> and then the y value into the linear equation. However, this wont work because no decimal places are allowed with these values...
I have also tried to stop flickering, but it did not work =(


Post any relevant code (You may choose to attach the file instead of posting the code if it is too long)
<Here's my code...updated>

Turing:

View.Set ("graphics:1000;600,position:center;center,offscreenonly") var x, y, x2, y2 : int  % X and Y are the coordinates of the FIRST Ball (Red) , and X2 and Y2 are the coordinates of the SECOND BALL (Blue) var y22 : real var slope, distance_between_centres : real x := 100 y := 100            %starting points for the two balls x2 := maxx div 2 y2 := maxy div 2 const slope1 : real := 1.732   %the slope in quadrant one and three, where angle Theta is 60 degrees to the horizontal const slope2 : real := 0.57735 %"" Theta = 30 degrees const slope3 : real := -0.57735 %quadrants 2 and 4...the slope becomes negative const slope4 : real := -1.732  %same thing..negative slope const r : int := 4          %changes the radius of the balls...yea, yea, go ahead laugh... const movedist : int := 150 %determines how close you need to get to the blue ball in order to to move it const speed1 : int := 8     %the speed of your ball const speed2 : int := 3     %the speed of ball 2 in horizontal or vertical - this vsalue determines how "fast" the blue ball runs away from the red ball const speed3 : int := 2          %speed of the blue ball (ball2) in diagonals  - as does this value...i only wish it could be a decimal value...until then, the diagonal speed is a slight bit faster than the vertical/horizontal value var chars : array char of boolean %var line1x : real := (movedist * (cos (30))):0:2   %what i Would* put in place of 130 below on the "drawline"...but the value cannot be a decimal..nor can i seem to round it... :0:2...doesnt seem to work for me %var liney1 : real := (movedist * (sin (30))) procedure blueball % to keep the two balls' program apart...easier to read     drawfilloval (x2, y2, r, r, blue) % draws the blue ball     drawoval (x2, y2, movedist, movedist, black)     % These values were derrived from finding the x and y values of a triangle whos hypotenuse was the "movedist" value..at the time these values were written the "movedist" value was 160     drawline (x2 - 130, y2 - 75, x2 + 130, y2 + 75, black) %draws the "section" lines, which provides a visual aid in determining the direction the blue ball will travel     drawline (x2 - 130, y2 + 75, x2 + 130, y2 - 75, black)     drawline (x2 + 75, y2 + 130, x2 - 75, y2 - 130, black)     drawline (x2 + 75, y2 - 130, x2 - 75, y2 + 130, black)     if (x2 - x) = 0 then % Eliminated the possibility that x and x2 are the same number so that we dont accidentally DIVIDE BY ZERO!...which would crash the program of course...         x := x2 + 1     end if     slope := ((y2 - y) / (x2 - x)) % finds the slope between the two balls     distance_between_centres := (sqrt ((x2 - x) ** 2 + (y2 - y) ** 2)) %finds the distance between the first(red) and second(blue) circles     put "Slope: ", slope : 9, " x: ", x : 3, " y: ", y : 3, " x2: ", x2 : 3, " y2: ", y2 : 3 %outputs the slope, x and y coordinates for the balls     % Diagonal movements     if slope < slope1 and slope > slope2 and distance_between_centres <= movedist and x > x2 and y > y2 then         x2 -= speed3         y2 -= speed3     end if     if slope < slope3 and slope > slope4 and distance_between_centres <= movedist and x > x2 and y < y2 then         x2 -= speed3         y2 += speed3     end if     if slope < slope1 and slope > slope2 and distance_between_centres <= movedist and x < x2 and y < y2 then         x2 += speed3         y2 += speed3     end if     if slope < slope3 and slope > slope4 and distance_between_centres <= movedist and x < x2 and y > y2 then         x2 += speed3         y2 -= speed3     end if     % X and Y movements     if slope < slope2 and slope > slope3 and distance_between_centres <= movedist and x > x2 then         x2 -= speed2     elsif slope < slope2 and slope > slope3 and distance_between_centres <= movedist and x < x2 then         x2 += speed2     elsif /*slope > -340 and slope < 200 and slope not= slope1 and slope not= slope2 and slope not= slope3 and slope not= slope4 and*/ y < y2 and distance_between_centres <= movedist then         y2 += speed2     elsif /*slope > -340 and slope < 200 and slope not= slope1 and slope not= slope2 and slope not= slope3 and slope not= slope4 and*/ y > y2 and distance_between_centres <= movedist then         y2 -= speed2     end if     /*      if slope > -340 and slope < 200 and slope not= slope1 and slope not= slope2 and slope not= slope3 and slope not= slope4 and y > y2 and distance_between_centres <= movedist then      y2 -= speed2      end if      */     /*if distance_between_centres <= movedist and y < y2 then  %THIS WAS ROUGH WORK...didn't work      y2 += speed2      end if      if distance_between_centres <= movedist and y > y2 then      y2 -= speed2      end if*/     %restricts blue ball from exiting boundaries, and allows red ball to push it around more     drawbox (40, 40, maxx - 40, maxy - 40, red) % comment this line if you DO NOT want to see the "restictions" box for the Blue Ball     if y2 < 40 then         y2 := y2 + speed2 % now, if the ball is moving diagonal, it can leave the screen...but that because i CANNOT let the speed be a decimal value...which would otherwise be: sqrt(x2**2 + y2**2)     end if     if y2 > maxy - 40 then         y2 := y2 - speed2     end if     if x2 < 40 then         x2 := x2 + speed2     end if     if x2 > maxx - 40 then         x2 := x2 - speed2     end if     % for some reason, the blue ball likes to slowly creep past the maximum "y" values it was permitted...so i fixed that with this..or this with that? lol     if y2 > maxy - 40 then         y2 := maxy - 40     elsif y2 < 40 then         y2 := 40     end if end blueball loop     cls     Draw.Box (20, 20, maxx - 20, maxy - 20, blue)     drawfillbox (21, 21, maxx - 21, maxy - 21, green)     Input.KeyDown (chars)     % moved the red ball according to input     if chars (KEY_UP_ARROW) then         y := y + speed1     end if     if chars (KEY_RIGHT_ARROW) then         x := x + speed1     end if     if chars (KEY_LEFT_ARROW) then         x := x - speed1     end if     if chars (KEY_DOWN_ARROW) then         y := y - speed1     end if     % restricts your ball from travelling off the screen     if y < 20 then         y := y + speed1     end if     if y > maxy - 20 then         y := y - speed1     end if     if x < 20 then         x := x + speed1     end if     if x > maxx - 20 then         x := x - speed1     end if     drawfilloval (x, y, r, r, red) %draws the red ball     blueball % runs the blueball code     drawline (x, y, x2, y2, black) % draws a line between the two balls, so you know which section your ball will fall into     View.Update     delay (20) % wait a bit, so the program does not to superspeed end loop

Please specify what version of Turing you are using
<v4.1.1>

[Zren]

This tutorial ought to help you. It's essentially the same thing since you just want to polar opposite of following (running away!).

http://compsci.ca/v3/viewtopic.php?t=17607&highlight=trigonometry

The difference is that you want the angle the dude is moving to be the other side of the circle. Half the full angle of the circle (arc length). In other words, you want to add 180* to the angle between your player (Mouse in the tutorial, Red dot for you), and the AI (blue guy).

So you'd want to add this to the source code from the tutorial.

wrote:

eAngle := 180 + setAngle (xm - eX (eTaleLenght), ym - eY (eTaleLenght)) % gets the angle from enemy to mouse

Before hacking away at your code though, look at Saad's post in the same thread, he uses another method that achieves the same thing, however it might be a little more related to your code.

To do what your asking though, we want to go in the opposite direction:
enemy.x -= xDir
enemy.y -= yDir