Trouble Shooting trig

[BenLi]

im trying to make a program to shoot a projectile and calculate the angle in which it was fired at. I get a error message saying "quit #100", help PLZ

code:

setscreen ("graphics:800;600,offscreenonly") const speed : int := 25 const startx := 100 const starty := 100 var shotx, shoty : real var mx, my, mb : int var deltax, deltay : real var b : real var ang: real loop     shotx := startx     shoty := starty     loop         mousewhere (mx, my, mb)         exit when mb = 1     end loop     deltay := my - starty     deltax := mx - startx     b:= Math.Distance (startx, starty, mx, my)         ang:= arcsind (((deltax **2) + (b**2) - (deltay**2))/2*deltax*b)         loop shotx:=shotx+(deltax/((Math.Distance(startx,starty,mx,my))/ speed)) shoty:= shoty+(deltay/((Math.Distance (startx, starty, mx, my)) / speed))         drawfilloval (round (shotx), round (shoty), 10, 10, red)         View.Update         cls       put "Angle is ", ang         exit when shotx > maxx + 10 or shoty > maxy + 10 or shotx < -10 or shoty < -10     end loop end loop

[HellblazerX]

sounds like you don't know how to use arcsind. Arcsind takes the original sine value, and returns the angle in degrees. So, originally, to determine the y-value, we have sine(theta) * hypotenuse. So, to find theta, we use sine inverse (y/hypotenuse). So, replace the line where you used arcsind with this:

code:

b:= Math.Distance (startx, starty, mx, my)     if b = 0 then         b := 0.0001     end if     ang:= arcsind (deltay / b)

The if construct is there incase the hypotenuse was 0, and you can't divide by 0.

Btw, you should slow down the speed of your projectiles, cuz they're very hard to see. Other than that, a great program. Are you planning to do anything with it?

[HellblazerX]

Sry, I forgot this in my first post. Add this piece of code after the arcsind function:

code:

if mx < startx then     ang = 180 - ang end if

Because arcsind only works for half of the circle, from -90 to 90, this part checks if we're working with the other half, and if so, changes the angle to the correct one

[BenLi]

thanks, i asked my comp sci teacher for the syntax for cos inversion, and he just said arcsind... maybe i should've asked how to use it

and yes, im using it for a gunbound like game, i haven't put in gravity yet though, any idea how to do that?

[Tony]

for gravity, just accelerate everything downwards by a constant during each tick of your game loop.

[BenLi]

But you would increase the grav value for every time it loops right?

i tried taht, didn't look good

[Cervantes]

No. Gravity is constant. (Assuming you don't care about the negligable amount by which the force of gravitation attraction decreases as you move up a couple of metres)

[Clayton]

for gravity you could do something like this

code:

const GRAV : real := 0.01 const RADIUS : int := 10 var x, y : real var yChange : real := 1 var count : int := 0 x := maxx div 2 y := 0 View.Set ("graphics,offscreenonly") loop     exit when hasch     loop         cls         Draw.FillOval (x, y, RADIUS, RADIUS, black)         View.Update         y += yChange         if count not= 1 then             yChange -= GRAV             exit when y = 0         else             yChange += GRAV             exit when y = 2         end if     end loop     yChange := 1     yChange := -yChange     if count not= 2 then         count += 1     end if     if count = 2 then         count := 0     end if end loop

something like that will create a more realistic jump with gravity (im not 100% sure that that will run perfectly, dont quote me on that one) experiment with it and see what you can come up with