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2D All the way! / Diagonal Sprite Movment

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kkun
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Posted: 10th Jun 2009 10:53
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Hey guys i'm new to the darkBasic scene and would like to be directed in how to program

a sprite moving in one way but would aim where ever the buttons are

eg if im moving up and i shoot down he'd face down while moving up.

a good example would be smash tv on the super nintendo.

i'm having problems with the diagonal shooting mainly. So if i hit left and down it'd shoot bottom left.
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chwilly
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Posted: 11th Jun 2009 07:34
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Think of
Y increment: UP as -1, DOWN as 1
X increment: LEFT as -1, RIGHT as 1

It doesn't matter what direction he is facing (each must be treated individually), if he is shooting down then Y increment = 1 and X increment = 0

So bottom(down)/left is: Y increment = 1 and X increment = -1
You use movement the same way

This is how I use it anyways
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kkun
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Posted: 11th Jun 2009 19:20
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Ah i see, i didnt actually think of that and assumed there was some crazy sin cos or tan formula associated with it.
thanks for that.
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NeX the Fairly Fast Ferret
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Posted: 13th Jun 2009 14:06
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Well, actually, no...

Movement along each axis when moving diagonally should be 0.70710678118654752440084436210485x what it is along a single axis when moving horizontally or vertically. sin( 45 ). Try it.

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chwilly
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Posted: 19th Jun 2009 08:16
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What the hell are you talking about? Thats about 70710678118654752440084436210485 times more complicating then it needs to be.
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Lilith
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Posted: 20th Jun 2009 00:11
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What he's saying is that if you take an object moving at, say, 10 units per frame along either the x or y and switch it to move 10 units along a 45 degree diagonal you have to change the amount it's moved along the x and y axis by a factor of roughly .7071067. Otherwise it moves faster on the diagonal than it does on the axes. If you continued to move the object 10 upf on both x and y the diagonal speed would be sqrt (200) = 14.14 units per frame.

You should always break the x and y components of the velocity into separate values with x being

velocity * cos(angle)

and y being

velocity * sin(angle)

This likely will give you non-integer values so it's best to use floats for maintaining position and convert them to integer values when passing them to the positioning functions.

Lilith, Night Butterfly
I'm not a programmer but I play one in the office
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chwilly
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Posted: 20th Jun 2009 01:42
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Pythagoras ez da bomb dude!

Anyway, your talking about regulating speed/velocity not direction. In a 2d sense, moving diagonal on the X/Y plane, say up and to the left, you are still just manipulating X/Y coordinates of the sprite reqardless of how you calculate speed, which is what I believe the question was. From what kkun was asking it appeared he was trying to figure out how the coordinate system works on the screen.
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