Can someone help with a math problem?
BlitzPlus Forums/BlitzPlus Programming/Can someone help with a math problem?
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| I have a turret that rotates to face the mouse. This is simple enough if I want the turret to just face that direction atan2 will do that. But, what I want it to rotate it slowly. I have a bit of code that works almost, haha. It will turn the turret CW or CCW depending on where the mouse is. The problem is when it crosses the 0 angle threshold. Say for example the turret is at 5 degrees and the mouse is at 355 degrees. The turret will turn CW 350 degrees even though it is longer. CCW is only 10 degrees away. I need a way to calculate the shortest route and move CW or CCW base on the answer. I have tried several things and can't get it working right. I can't even work out in my mind what I need :( Here is the base code. ;turn turrent ;find angle to turn to calc = 360-ATan2(tankx- MouseX() ,tanky-MouseY()) ;set angle to 0 to 359 If calc>359 Then calc=calc-359 If calc<0 Then calc = 359+calc ;figure out if turn CW or CCW, which is closer ;turrentangle compared to calc ;turn CW If calc > turrentangle Then turrentangle = turrentangle + turrentspeed ;turn CCW ElseIf calc < turrentangle Then turrentangle = turrentangle - turrentspeed EndIf Thanks for any insight you can give. CTP |
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sorry guys, I worked it out.;turn turrent ;find angle to turn to calc = 360-ATan2(tankx- MouseX() ,tanky-MouseY()) ;set angle to 0 to 359 If calc>359 Then calc=calc-359 If calc<0 Then calc = 359+calc ;figure out if turn CW or CCW, which is closer ;turrentangle compared to calc If calc<90 And turrentangle>270 Then turrentangle = turrentangle + turrentspeed ElseIf calc>270 And turrentangle<90 Then turrentangle = turrentangle - turrentspeed ;turn CW ElseIf calc > turrentangle Then turrentangle = turrentangle + turrentspeed ;turn CCW ElseIf calc < turrentangle Then turrentangle = turrentangle - turrentspeed EndIf Please if anyone knows a easier way to do this plase tell me. I had to make to more conditional statements to handle it. Seems like there should be a simple math function to tell this but maybe not. |
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| There's a much easier way to do it! First of all, the arguments of atan2 should be dy,dx, not dx,dy like you've got it. I haven't got blitzplus though, so maybe it's different. Anyway, so you take work out your angle calc, which is where you want to point to, and you subtract turretangle from it to get 'anglediff'. You've got a few possibilities for what anglediff can be: a) If it's in the range -180 to +180, you can use it straight away. This range covers an entire rotation and is the smallest range to do so, so you want andiff to end up in this range. b) If it's less than -360 or bigger than +360, you need to add or subtract multiples of 360 until you get in the range -360 to +360. You can do this very quickly with the Mod operation. c) Now, if andiff is still less than -180, add 360, so -270 would become +90. And if it's bigger than +180, subtract 360. d) So now andiff gives you the shortest angle to turn to face 'calc'. If andiff is positive, you need to turn clockwise, and if it's negative you need to turn anti-clockwise. So you can use Sgn(andiff) just to get the sign of andiff, and multiply that by 'turretspeed' to turn at a constant rate. I know this all sounds complicated, but this is just my mathematical explanation for why this method is correct. You can implement it in 4 lines: andiff = (calc - turretangle) mod 360 if andiff < -180 Then andiff = andiff + 360 if andiff > 180 Then andiff = andiff - 360 turretangle = turretangle + sgn(andiff) * turretspeed |
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| Your right about dy,dx but hacking around with it like i was I was only able to get it to work dx,dy? Maybe because I was adjustingit by 360? Anyway I have bee trying to implement the method your have shared with me, thanks by the way, and I get a curious problem. with the mouse pointer straight up at angle 0 the calc returns 90. ;find angle to turn to calc = ATan2(tanky#-MouseY(),tankx#-MouseX()) andiff = (calc-turretangle) Mod 360 If andiff < -180 Then andiff = andiff + 360 If andiff > 180 Then andiff = andiff - 360 turretangle = turretangle + Sgn(andiff) * turretspeed ;make sure turretangle to be in the range of 0 to 359 If turretangle < 0 Then turretangle = 359+turretangle If turretangle > 359 Then turretangle = turretangle-359 ;draw layered image DrawImage tankGFX(angle),tankx#,tanky# DrawImage turretGFX(turretAngle),tankx#,tanky# ;data check Color 0,0,0 Text 50,10,calc Text 50,20,andif Text 50,30,turretangle Text 50,40,angle Text 50,50,tankx# Text 50,60,tanky# I have tried making dy,dx = mouse-tank and tank-mouse, but I again made it work by hacking around with it because I dont really understand it :( and by adding 270 to the point to angle it works calc = 270+ATan2(tanky#-MouseY(),tankx#-MouseX()) I am assuming angle 0 points up is this a wrong assumption? Does angle 90 point up? and is that why I have to adjust it by 270? CTP |
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| You can find a description of the angle system here. This was written for Blitz3D, hence the confusing reference to the y-axis pointing up in the 3d world. |
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Just a quick note which doesn't greatly help. Instead of:If turretangle < 0 Then turretangle = 359+turretangle If turretangle > 359 Then turretangle = turretangle-359You can just use: turretangle = turretangle Mod 360 |
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| Thanks for the tip Gfk, Mod is another command I don't fully understand. Will have to play with it and check out how it returns. |
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