Following the mouse...

[ZeroPaladn]

I was wondering how to make lets say... a bullet go in the directoin of the mouse when fired? I'm at a loss on how to do it. I've heard of using trig and the x and y coords of the mouse and the player and use the pythagoream theorm, but im still at a loss.

PS. Its been a while everyone.

[Cervantes]

Yes, trig and Pythagorean theorem will be needed. What have you got so far?

Draw these things out on paper. It's a lot easier to work out the equations there than type them immediately into your code.

[MysticVegeta]

Well you will need Pythagoreans for the shortest distance (hypotneuse) between the bullet and the mouse (x, y). And the trig to figure out what angle it should be shot at. It would be a right triangle so you can use your sin, cos and tan no prob

[ZeroPaladn]

good idea cervantes, ill draw it out, and see what i come up with then. so let me get this straight, i use the pythagorean therom to find the shortest distance between my char and the mouse coords, then figure out the angle of that using trig, then fire off the bullet in said direction?

[do_pete]

MysticVegeta wrote:

Well you will need Pythagoreans for the shortest distance (hypotneuse) between the bullet and the mouse (x, y).

Why do you need to find the shortest distance? Don't you just need the coordinates of the mouse and character to calculate the angle?

[BenLi]

actually, you will only need trig if you actually have to know what angle fired at. See what I said at this silmilar post

http://www.compsci.ca/v2/viewtopic.php?t=13473

[ZeroPaladn]

if only i understood the code... DAMN I HATE TRIG!

[Ultrahex]

There Is Also This Way Using Getting The Angle... Here is an example program I just wrote cause i was bored and am procrastinating other assignments

code:

View.Set ("offscreenonly") var mx, my, mb : int %Mouse Variables var bulletx, bullety : real := 50.0 %Bullet Location var velx, vely : real := 0 %Bullet Velocities (Split into x and y) var pointx, pointy : int := 50 %Point Shooting From var tempx, tempy : int %Used to Get Point End of Line Drawn from Shooting Point % Function Written By Ultrahex to Determine Angle in Degrees (Also Includes Exceptions) % This Code is NOT efficiently Written !!! function getAngle (x1, y1, x2, y2 : int) : real     if ((x2 - x1) ~= 0) then         if ((x2 - x1) <= 0) then             result arctand ((y2 - y1) / (x2 - x1)) + 180         else             if (arctand ((y2 - y1) / (x2 - x1)) < 0) then                 result arctand ((y2 - y1) / (x2 - x1)) + 360             else                 result arctand ((y2 - y1) / (x2 - x1))             end if         end if     else         if ((y2 - y1) <= 0) then             result 270         end if         if ((y2 - y1) >= 0) then             result 90         end if     end if end getAngle loop     cls %Clear Screen     Mouse.Where (mx, my, mb) %Set Mouse Point Variables     /* Calculations for Line */     tempx := round (cosd (getAngle (pointx, pointy, mx, my)) * 100)     tempy := round (sind (getAngle (pointx, pointy, mx, my)) * 100)     /* Bullet Movement Calculations */     bulletx += velx %Move Bullet By Current Velocity Along X-Axis     bullety += vely %Move Bullet By Current Velocity Along Y-Axis         /* OUTPUTS */     put "Angle Between Mouse and Point Is: ", getAngle (pointx, pointy, mx, my) %Display The Angle Between Right and Mouse Location     put "D:[", mx - pointx, ",", my - pointy, "]" %Display Mouse Point Compared to Shooting Point     /* Drawing */     drawfilloval (pointx, pointy, 3, 3, black) %Shooting Point     drawfilloval (round (bulletx), round (bullety), 3, 3, purple) %Bullet     drawline (pointx, pointy, pointx + tempx, pointy + tempy, red) %Line From Shooting Point         if (mb = 1) then %If Mouse Clicked...         %Reset Bullet Location to Point Of Shooter         bulletx := pointx         bullety := pointy         %Get The Velocity dependant on Angle (Much Like Slope)         velx := cosd (getAngle (pointx, pointy, mx, my)) * 5         vely := sind (getAngle (pointx, pointy, mx, my)) * 5     end if         View.Update %Update Screen     delay (20) %Delay end loop

As Long as You Understand "SOH, CAH, TOA" you should understand how i am getting to this (Remeber Sin(theta) = y/x and all that. Remeber Don't just take the code, it provides a guideline even though it probably is more then that for some and i bet i will see my code in a turing program soon but that is how life works i suppose. Hope this clears a few things up? possibly :/ Ask Questions if You Would Like.

[zylum]

all you need is similar triangles. take a look at the attached image... there are two similar triangles. with similar triangles you can do something like height_1 / base_1 = height_2 / base_2 and solve for an unknown quantity if you have the other three. in our case, we have the hypoteneus of the small triangle (which represents the velocity vector), the base, hieght and hypoteneus of the big triangle (ie where the mouse is relative to the charater). we want the find the components of the velocity vector (dx and dy) which are represented by the base and height of the little triangle. so we would use the formulas dx / speed = (mx - x) / hypoteneus and dy / speed = (my - y) / hypoteneus. rearange to isolate dx and dy and solve.

heres a sample code:

code:

setscreen ("offscreenonly") const x := maxx div 2 const y := maxy div 2 const s := 100 var mx, my, md : int var d, dx, dy : real loop     mousewhere (mx, my, md)     d := sqrt ((mx - x) ** 2 + (my - y) ** 2)     dx := s * (mx - x) / d     dy := s * (my - y) / d     drawline (x, y, round (x + dx), round (y + dy), black)     drawoval (x, y, s, s, grey)     View.Update     cls end loop

[zylum]

sorry, heres the picture:

[ZeroPaladn]

Thanks to you both, Zylum and Ultrahex. I understand it now! I liked Zylum's more simplistic method, although you can glitch out Zylum's program (just hover the mouse of the exact centre of the circle, Ultrahex's just points it straight down). Bits to you both!

+25 Bits to Zylum and Ultrahex

Thanks again guys!

[Clayton]

My oh my, zylum, people seem to like giving bits to you dont they, maybe it has something to do with that even 1000 bits sitting there that they dont like?

NOTE: zylum is a MOD, his bits are SET

[zylum]

maybe they give me the bits in a gesture of appreciation. and since you're so fond the rules, maybe you should follow them and stop spamming. [Rules]

anyhoo, to fix the division by zero problem, i usually add a very small value to the denominator. technically, if the denominator is equal to the negative of the value i add, it will also be division by zero but that is far less likely than it would otherwise be..

code:

setscreen ("offscreenonly") const x := maxx div 2 const y := maxy div 2 const s := 100 var mx, my, md : int var d, dx, dy : real loop     mousewhere (mx, my, md)     d := sqrt ((mx - x) ** 2 + (my - y) ** 2) + 1e-4     dx := s * (mx - x) / d     dy := s * (my - y) / d     drawline (x, y, round (x + dx), round (y + dy), black)     drawoval (x, y, s, s, grey)     View.Update     delay (50)     cls end loop

[TheOneTrueGod]

why don't you just do an "if" check? it'll eliminate any "stupid" things from happening, like the -1e4 value cropping up.. (Though since you used sqrt, this isn't possible in this particular instance, but I have seen a few times where the program you provided COULD result in a division by zero error...)