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Drawing Arcs (For a cannon game)

Update:11-30Source: network consolidation
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I was wondering if anyone could help me out with a java program I'm trying to write. I need to draw an arc from a specific location (which I can handle) but I want it to simulate a cannon fire. All I'm really worrying about at this time is involving gravity - I have no idea how to do this. I'm asking the user for an angle, and the velocity.
If anyone can help explain an equation that would draw an arc please do so! :)
(I've tried looping through the x coordinates which seems to work well, but I don't have a proper equation for y :P)

The Best Answer

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I think you wouldn't draw an actual arc at all. Instead you'd plot points. You know the cannon velocity. From the cannon angle you can get the X and Y delta (Amount of change in X and Y per time click).
For each time click you plot a point in the X direction - wind speed and in the Y direction - gravity.
For example, let's say that that we ignore wind and we're just shooting from left to right and we're shooting at a 45 degree angle. Y = mX + b tells us that the rise and run for a 45 degree angle are the same. And just for fun let's say that gravity is 0.2 So for each plot you take the previous plot and add subtract the energy lost to gravity. But your X direction stays constant because of the lack of wind resistence. Here we go:
Turn is the time click, X and Y are your delta and LocX and LocY are the location of the dot relative to the end of the cannon
Turn  X   Y    LocX   LocY
1     1   1     1       1
2     1   0.8   2       1.8
3     1   0.6   3       2.4
4     1   0.4   4       2.8
5     1   0.2   5       3.0
6     1   0     6       3.0
7     1  -0.2   7       2.8
8     1  -0.4   8       2.4
9     1  -0.6   9       1.8
10    1  -0.8   10      1.0
11    1  -1.0   11      0So after 11 turns the shell crashes into the ground (Assuming level ground) For uneven ground you just test LocX and LocY for an intercept with your ground level.
You can see how you would do the same thing for wind resistence as well. That would simply change your X increment.
Hope that helps
Greg
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