Drawing Arcs (For a cannon game)

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)

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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PDF on Illustrator doesn't indicate how to select the Arc tool. Extract from toe pdf follows:
Draw arcs
1 Select the Arc tool . (HELP -- I CAN'T LOCATE THE ARC TOOL).
2 Do one of the following:
• Position the pointer where you want the arc to begin, and drag to where you want the arc to end.
• Click where you want the arc to begin. In the dialog box, click a square on the reference point locator to determine the point from which the arc is drawn. Then set any of the following options, and click OK.
Length X-Axis
Specifies the width of the arc.
Length Y-Axis
Specifies the height of the arc.
Type
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Base Along
Specifies the direction of the arc. Choose X Axis or Y Axis depending on whether you want to draw the base of the arc along the horizontal (x) axis or vertical (y) axis.
Slope
Specifies the direction of the arc’s slope. Enter a negative value for a concave (inward) slope. Enter a positive value for a convex (outward) slope. A slope of 0 creates a straight line.
Fill Arc
Fills the arc with the current fill color.
Note: To see a dynamic preview of the arc as you set options, double-click the arc tool in the Tools panel.

You're welcome.
Can i suggest that you explore al the tools there are drop down menus and on the panels as well in the upper right hand corner there is a drop down with useful functions and options. Also look at the control panel under the menu bar as you change tools to see the option each tool has and also some tools have further settings if you double click the icon in the tool bar other have option if you click in the document window once you have selected them.
But the best advice I can give you is to buy Mordy Goldings book Real World Illustrator CS 4 he also has one for the suites, it is a worthwhile investment.

Need help/hints/tips with a method for connect 4 game.

Hi!
I'm currently trying to get my "movepiece"-method to make it so that players can only drag a piece into the empty square at the bottom row, and if the square is not empty the method will move up one row and check if it's empty if not, repeat until
6 are checked if no one is empty then move is invalid.
I've been trying out while loops and for loops but i think i might set the wrong conditions for exiting the loop...
Here the code for the method without any loops simply adds pieces.
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/// Method that performs the actual move.
/// The old piece gets overrun by the attacking piece.
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/// </summary>public Piece[,] MoveAttackpiece(int[,] changearray)
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int origY = changearray[0, 1];
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int targetY = changearray[1, 1];
pieceArray[targetX, targetY] = pieceArray[origX, origY]; //swap
return pieceArray;
The game is using winforms and a 2D array(pieceArray)to draw the game board
I'm using a Constants class for declaring the height and width of the board, which the pieceArray is based on, Namely const int BOARDESIZEx and BOARDERSIZEy.
And while i'm at it when i did different loops for tryng to make the piece move down/up (based on if a square in bottom row was empty or not) the program crashes and i get the "Null Reference Exception unhandled"
at this part in the game.CS (the earlier code reside in a class named Squares.cs)
if (changearray != null)
//Building string to print (split over several rows for readability but also to avoid calculations)
Piece attackpiece = pieceArray[changearray[1, 0], changearray[1, 1]];
string message = "";
if (move % 2 == 1) message += "TURN " + move / 2 + ":\r\n"; //integer division, as there are two draws per turn
message += attackpiece.Name + ": "; //Walker:
message += IntegerToChar(changearray[0, 1]); //Walker: A
message += (changearray[0, 0] + 1) + " - "; //Walker A1 -
message += IntegerToChar(changearray[1, 1]); //Walker A1 - B
message += (changearray[1, 0] + 1); //Walker A1 - B2
if (move % 2 == 0) message += "\r\n"; //blank row inserted after each completed turn
Board.PrintMove(message);
I've tried making
While(piecearray[targetX, targetY]!=null)
pieceArray[targetX, targetY]==pieceArray[targetX, targetY +1];
return array;
but that didn't work and i don't really know how to make the game start at bottom row.
I appreciate any help or tips on how to get this to work since it's the only thing left for making the game work as intended.
Cheers and thanks for reading.
PS: if there's anything you wonder just ask and i'll explain as much as i can.
Regards Gabbelino
Student at the University of Borås, Sweden

Let's look at what's wrong with the following code.
While(piecearray[targetX, targetY]!=null)
pieceArray[targetX, targetY]=pieceArray[targetX, targetY +1]; // I assume the "==" in your post above was a typo.
Suppose, for the sake of argument, that targetX is 2 and targetY is 3, and that pieceArray[2,3] is not null. The line inside the loop will then become...
pieceArray[2,3] = pieceArray[2, 4];
...and this line will keep being executed as long as pieceArray[2,3] is not null, which if pieceArray[2,4] is not null will be forever (infinite loop).
I suspect that your loop should look something like this...
for(int i = 0; i < BOARDSIZEy; i++)
// Look for the first available square in the target column.
// When found, set the piece on that square then break out.
if(pieceArray[targetX, i] == null)
pieceArray[targetX, i] = pieceArray[origX, origY];
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��
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��
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��
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Radar Accruacy �- not disclosed
��
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Drawing Arcs (For a cannon game)

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