Custom 8 direction movement, problems with speed

Ok, basically for the player speed, I have a global value, with a default value of 4.

Basically, my movement is working like this:

Repeat while [Player moves Right]:
-Set X Pos of Player to X Pos of Player + Speed

Then I went and did this for Up, Down, and Right directions, with the appropriate calculations. This allows the player to move around at the desired speed, however, I have noticed an anomaly. When moving at an angle, like say Up+Right, it seems like the player is moving slightly faster than when moving just Up or Right. It happens for all the 4 angle movements.

I'm a little confused by what is going on. To make things more clear, for Up movement I have:

Repeat while [Player Moves Up]:
-Set Y Pos of Player to Y Pos of Player - Speed

I have tried adjusting the speed when an angled direction is pressed like if Up+Right is pressed, then set Speed to [value], but this didn't work.

Basically, I want the player to move the same speed whether its the 4 regular directions or the 4 angles in 8 direction movement. At the moment, with what I'm doing, the player moves slightly faster while going one of the angle directions, even though I never change the Speed variable in any events.

Any ideas?

Well for the time being I just stopped trying to do a custom movement and use the built in 8 direction movement. But I'd still be interested to know in why I was seeing a speed difference.

Speed difference is a problem with the maths. If you think about it, you have the speed of 4 in the X and in the Y, which gives you a resultant hypotenuse (it makes a vector triangle) of almost 6. So yes, your player is moving at 1.5 times the speed it should be.

What you need for an accurate 8-direction movement is a bit of trigonometry. For the Y, multiply your speed by the sin of the angle...

4*sin(0)
4*sin(45)
4*sin(90)

... all the way up to 4*sin(315) in 45 degree increments. Then for the X multiply your speed by the cos of the angle:

4*cos(0)
4*cos(45)
4*cos(90)

... and so on again. That will give you an accurate movement. :)

Good luck!

Awesome! Thank you!

As you can probably tell, math isn't my strongest suit lol.

The thing is - as a pixel is square, moving one pixel up, or one pixel right, is shorter than moving one diagonally:

move right:
x = 10
y = 0
distance = Sqrt(10*10 + 0*0) = 10

move diagonal:
x = 10
y = 10
distance = Sqrt(10*10 + 10*10) = Sqrt(200) = 14,1421.. = 10 * Sqrt(2)

So if you want the correct diagonal movement, just divide the speed by Sqrt(2) (the square root of 2, or 2 to the power of 0.5).

You could do this by determining on how many axises the player moves and use that within the Sqrt() (or whatever it is in MMF):
speed = 10 / Sqrt(speed_x/speed_x + speed_y/speed_y)
if he moves on one axis, this will become Sqrt(1) = 1 and on two axises Sqrt(2) and on none Sqrt(0) = 0. Yay :D

Thinking about it, if you already have the angle, DizzyDoo's solution is a lot more elegant :P

Okay I think I got the calculations down for the angles, but I was wondering what I need to do to implement the speed in MMF.

Like before I was doing X Pos = X Pos + Speed for moving right.

So, using the calculation for moving right, I would assume that would be 4*cos(0), so would I do X Pos = X Pos + (4*cos(0))?

Or am I not understanding this correctly?

use X Pos = X Pos + (4*cos(0))
Y Pos = Y Pos - (4*sin(0))

the 4 is the speed
the 0 is the angle (right = 0, up = 90, left = 180, etc..)

Quote:

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Originally Posted by Mook06

use X Pos = X Pos + (4*cos(0))
Y Pos = Y Pos - (4*sin(0))

the 4 is the speed
the 0 is the angle (right = 0, up = 90, left = 180, etc..)

---

Okay thanks! :)

For some reason this is not working for me. When I move my person down and to the left, he's not moving at a 45 degree angle, and he's moving very slow. I'm using a speed of 2, but when I switch it to a speed of 4 it doesn't change. Does this have anything to do with the fact that I'm trying to move an object a fraction of a pixel?

XPos = XPos + (Speed*cos(angle))
XPos = XPos + (2 * cos (225)) which equals -1.41

Am I doing this wrong?

And I found a solution (posted below just in case anyone else runs into this thread).

The answer is to hold an object's position in an alterable value, and adjust that with the trig statements. Since alterable values can hold decimals, it keeps your position accurate. You implement this by just always setting the position of your object to that alterable value.

I believe you need to store the resulting x/y positions as floats(because mmf can't set the position to a float only an integer) and then set the x and y to those values.

So do what you did except set a value instead of the x/y pos, then another event that sets the x/y pos to those values.

edit: beat me to it :P