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Okay, I feel a little stupid here. I've forgotten most of my Highschool math, which is a shame.

Here's the rundown: I am attempting to get a sprite to pick up the location of the player's sprite, and move to that location, then keep on a steady line and straight through it. Since I have no diagrams to show, I'll help you draw a mental picture.

EnemySprite is at location (x1, y1). PlayerSprite is at location (x2, y2). I want EnemySprite to rotate to PlayerSprite's angle, then move quickly to, then through it.

The code I am using is:

function enemymove(CurrentSprite, AttackX, AttackY)
If AttackX = 0 and AttackY = 0
AttackX = Sprite X(EnemySprite) - Sprite X(CurrentSprite)
AttackY = Sprite Y(EnemySprite) - Sprite Y(CurrentSprite)
Rotate Sprite EnemySprite, ATAN(AttackY/AttackX)
endif
Move Sprite EnemySprite, 20
endfunction

In theory, this should work without an issue. However, it seems every time the function is called, AttackX and AttackY are reset to 0, causing the EnemySprite to dart about erratically.

Additionally (as silly as this sounds,) I get an error when the PlayerSprite and EnemySprite are on the same axis. I know why this is, however, because AttackX or Attack Y = 0.

Can anybody help me? I know I'm not offering alot of information, but any help would be greatly appreciated. Also, the EnemySprite does not have to rotate, I just did that to make the movement easier on myself. Thanks in advance,

Jeremy R. Mahon

Hmm. Im not really sure I fully understand your code, But I will try to help any how.

Im assuming (ass outta you and me) that you want the enemy to track the player, but only update his direction every so often so the player can get away.

This code will have the green box be controlled by the mouse. The red box will go after it every 1000 loops.


EDIT:
And this code will have the red box update his direction when he gets to the edge of the screen.
sync on
sync rate 100

box 0,0,100,100
get image 1,0,0,20,20,1
cls


player = 1;
playerX = 0; playerY = 0;
playerImage = 1;


enemy = 2;
enemyX = screen width()/2;enemyY = screen height()/2;
enemyImage = 1;

enemyUpdate = 1;
enemySpeed = 5;
enemyAngle = 0;

sprite enemy,enemyX,enemyY,enemyImage
set sprite diffuse enemy,100,0,0
offset sprite enemy,sprite width(enemy)/2,sprite height(enemy)/2


do
playerX = mouseX()
playerY = mouseY()
sprite player, playerX,playerY,playerImage
set sprite diffuse player, 0,100,0
offset sprite player,sprite width(player)/2,sprite height(player)/2


if enemyUpdate = 1
enemyUpdate = 0
RotateToPoint(enemy,sprite X(enemy),sprite Y(enemy),sprite X(player),sprite Y(player))
endif
move sprite enemy,enemySpeed

if (sprite X(enemy) > screen width()) OR (sprite X(enemy) < 0) OR (sprite Y(enemy) < 0) OR (sprite Y(enemy) > screen height())
enemyUpdate = 1
endif

sync
loop


Function RotateToPoint(SpriteNum,Xo,Yo,Xd,Yd)

X = Xo - Xd
Y = Yo - Yd;

spriteAngle = -atanfull(X,Y)
rotate sprite spriteNum,spriteAngle

Endfunction

I appreciate it, but this actually causes the enemy sprite to shoot off in a 45 degree angle in the opposite direction. Lol. So, here is something I have been considering:

Basic trig/geometry, can't remember which, states that the slope of a ray (a straight line with a single endpoint) is determined with the equation slope = Ay - By / Ax - Bx. The equation for "y" at any point on the line is: y = slope*x + y-intercept. The intercept is at which point the line meets the y-axiz. This can be determined using the equation: intercept = y - slope*x. Now, in a two dimensional drawing test, this equation worked nearly flawlessly. However, when I plugged it into my program, my EnemySprite was stuck moving along the X axis, with the Y axis remaining unchanged. Here's my test code.

HIDE MOUSE
SYNC ON

OriginX = 480
OriginY = 80
TargetX = 320
TargetY = 240
NextX = OriginX

REPEAT
DOT OriginX, OriginY
DOT TargetX, TargetY

EndX = (OriginX - TargetX)
EndY = (OriginY - TargetY)
slope = EndY/EndX
intercept = OriginY - (slope*OriginX)

NextY = (slope*NextX)+intercept

IF EndX > 0 THEN NextX = NextX-1
If EndX < 0 THEN NextX = NextX+1
DOT NextX,NextY

SYNC

UNTIL MOUSECLICK()=1 OR ESCAPEKEY()=1
SHOW MOUSE
END

Did you really need to post this on multiple boards?


http://forum.thegamecreators.com/?m=forum_view&t=137826&b=1

Yeah, sorry about that. I first posted to this one, then saw another post that suggested programming posts just be made to the DarkBasic Pro Newcomers board, so I attempted to post my issue there instead.

I wasn't expecting anyone to reply to the post here, but when I got a response, I couldn't just leave this one hanging.

My code makes them go the wrong way?!
I tested it on mine and they were fine... That is a strange one.