Arctan in J2ME

Presenting:

// calculation functions
public class Calculation {

// Because J2ME has no floating point numbers,
// some sort of fixed point math is required.
// My implementation is simply to shift 10 places.
// for example, 1024 (>> 10) = 1
// and 512 (>> 10) = 0.5
public static final int[] CosTable90 = {
1024, 1023, 1023, 1022, 1021, 1020, 1018,
1016, 1014, 1011, 1008, 1005, 1001, 997,
993, 989, 984, 979, 973, 968, 962,
955, 949, 942, 935, 928, 920, 912,
904, 895, 886, 877, 868, 858, 848,
838, 828, 817, 806, 795, 784, 772,
760, 748, 736, 724, 711, 698, 685,
671, 658, 644, 630, 616, 601, 587,
572, 557, 542, 527, 512, 496, 480,
464, 448, 432, 416, 400, 383, 366,
350, 333, 316, 299, 282, 265, 247,
230, 212, 195, 177, 160, 142, 124,
107, 89, 71, 53, 35, 17, 0
};

public static final int[] AtanTable = {
0, 1, 2, 3, 5, 6, 7, 8, 10, 11,
12, 13, 14, 16, 17, 18, 19, 20, 21, 22,
23, 25, 26, 27, 28, 29, 30, 30, 31, 32,
33, 34, 35, 36, 37, 37, 38, 39, 40, 40,
41, 42, 43, 43, 44, 45
};


// angle calculation function based on x = x1 - x2, y = y1 - y2
public static boolean ArcTan(int x, int y, AngleArray sincos)
{
int angle = atan( y, x );
if (angle == -300)
return false;

int rotangle = abs(angle) % 90;

int cos = CosTable90[rotangle];
int sin = CosTable90[90-rotangle];

if (angle >= 270) // quadrant IV
{
int tCos = cos;
cos = sin;
sin = -tCos;
}
else if (angle >= 180) // quadrant III
{
cos = -cos;
sin = -sin;
}
else if (angle >= 90) // quadrant II
{
int tCos = cos;
cos = -sin;
sin = tCos;
}


sincos.sin = sin;
sincos.cos = cos;

return true;
}


/// returns angle 0->359 in degrees
public static int atan( int Y, int X )
{
boolean swap = false;

int top = abs(Y);
int bottom = abs(X);
if (top > bottom)
{
int btemp = bottom;
bottom = top;
top = btemp;
swap = true;
}
else if (bottom == 0)
return -300;

// this should keep index inbounds [0, 45]
int index = (top * 45) / bottom;
int angle = AtanTable[index];

if (swap)
angle = 90 - angle;

// X & Y += 180
// X & !Y = ...90
// !X & Y = ... 270
if ( (X < 0) && (Y < 0) )
angle += 180;
else if (Y < 0)
{
angle = 90 - angle;
angle += 270;
}
else if ( X < 0)
{
angle = 90 - angle;
angle += 90;
}

if (angle == 360)
angle = 0;

return angle;
}

// for good measure, sin and cos functions
public static int sin( int angle )
{
int rotangle = abs(angle);
while (rotangle > 89)
rotangle -= 90;

int cos = CosTable90[rotangle];
int sin = CosTable90[90-rotangle];

if (angle >= 270) // quadrant IV
sin = -cos;

else if (angle >= 180) // quadrant III
sin = -sin;

else if (angle >= 90) // quadrant II
sin = cos;

return sin;
}

public static int cos( int angle )
{
int rotangle = abs(angle);
while (rotangle > 89)
rotangle -= 90;

int cos = CosTable90[rotangle];
int sin = CosTable90[90-rotangle];

if (angle >= 270) // quadrant IV
cos = sin;

else if (angle >= 180) // quadrant III
cos = -cos;

else if (angle >= 90) // quadrant II
cos = -sin;

return cos;
}

}

Stiria

Stiria is a cell phone game I conceived of in late 2005/early 2006, involving a rather Kirby-like (), friendly ice cube as the playable character. The ice guy character (who I'm not sure if I even named), initially was to have all sorts of transformations in his quest to conquer/survive the difficulties of outer space and its wacky, varying gravity.

Shortly after I thought of the project, the first videos of Super Mario Galaxy came out -- and I felt a certain sense of being beaten to the punch. The project laid on the backburner

for a while, until I had to come up with a 4 week project for the final part of a software design course at the University of Illinois. I picked up the project then, and 4 weeks and a painful amount of work later, I had this to show for it:

Written in J2ME (now called java micro edition, or JME) using the Java Wireless Toolkit, the current version involves 40 or so planets floating around in space and exerting their gravity on the little guy.

The game in its present form is a single level without a real objective -- in the short time frame I had I was unable to finish a boss to end the level with. I have worked on the game some in the half-year since, but mostly on the underlying code to speed up the process. That said, I'm hoping I can find some time to come back to and finish the one level demo, at the very least. When I do I will post it here.

I have also considered this game a candidate for the Nintendo DS system, utilizing the DS's touchscreen. Taking on a DS homebrew project is another matter entirely, however. =)


Download both files to try on Java-supported cell phone (~152 kb total):

Demo 1 -- Java executable + installer (July 30, '08)

Newest beta release: 0.9.09