### Tank rotation

Hey everybody

I was wondering how i could simulate tank like movement.
What i was planing on doing is changing the rotation using left and right keys (Already using a library for input) then moving the tank with both the up and down keys. Usually movements pretty easy as in if the right button is pressed then increase the x coord but i wouldnt know how to do that with rotation. Sorry, its kind of hard for me to explain.
 ``12345678`` ``````Tank heading += TurningRate * LeftKeyPressed Tank heading -= TurningRate * RightKeyPressed Tank X Position += cos(Tank heading) + MovementRate * FwdKeyPressed Tank X Position -= cos(Tank heading) + MovementRate * AftKeyPressed Tank Y Position += sin(Tank heading) + MovementRate * FwdKeyPressed Tank Y Position -= sin(Tank heading) + MovementRate * AftKeyPressed``````
Why multiply the turning rate by LeftKeyPressed?
The exact implementation will differ depending on what libraries you're using to handle keyboard input; however, the rough logic is as follows.

 ``12345678910111213141516171819`` ``````if (W == Pressed) { location.x += (cos(0.017453277777 * heading)) * speed; location.y += (sin(0.017453277777 * heading)) * speed; } else if (S == Pressed) { location.x += (cos(0.017453277777 * heading)) * (speed * -1); location.y += (sin(0.017453277777 * heading)) * (speed * -1); } else if (A == Pressed) { heading -= 1; if (heading < 0) heading = 360; } else if(D == Pressed) { heading += 1; if (heading > 360) heading = 0; }``````

Hopes this helps. If you happen to be using SFML I can help you with implementation
Its not really working as expected. It only moves if the angle is just right and even then it just moves up.
Heres my code
 ``12345678910111213141516171819202122232425262728293031323334353637383940414243`` ``````void CheckKeys() { if (!kLeft && !kRight && !kUp && !kDown) { KeyDown = false; return; } KeyDown = true; if (kLeft) { if (KeyCounter >= KeyTick) { TankRotation -= 1; Redraw = true; KeyCounter = 0; } } if (kRight) { if (KeyCounter >= KeyTick) { TankRotation += 1; Redraw = true; KeyCounter = 0; } } if (kUp) { if (KeyCounter >= KeyTick) { TankX += (cos(0.017453277777 * TankRotation)) * Speed; TankY += (sin(0.017453277777 * TankRotation)) * Speed; Redraw = true; KeyCounter = 0; } } }``````

and im drawing it using this
 `` `` `` al_draw_rotated_bitmap(Tank, 32, 32, TankX, TankY, TankRotation*0.017453277777, NULL);``

Tank is the bitmap im drawing, both 32s are the x and y values of the middle of the bitmap, the next to arguments are the screen coords im drawing to, and the next is the angle to rotate by
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closed account (o1vk4iN6)
Well for converting from deg to rad I would use a name instead of the actual number or an inlined function might be even better. It also seems everything is a global variable, why not make a class call it, vec2 use that for position instead, then make a class for tank or entity to hold the position etc...
Last edited on
Well how would you convert it exactly?
And i know everythings a global right now, im just going to leave it as is right now.
closed account (o1vk4iN6)
It's a simple mathematical equation you learn in highschool. 0.017blahblah is just PI / 180. It really is simple when you think about it. 2PI is a complete circle in degrees it is 360, so 2PI/360 is rad per degree (can be simplified to PI/180) that multiplied by any degree will get you the radians, which is what all the mathematical functions use.

Why start a bad habit ? Save it now by removing all the globals before it's too late.
Oh thats why i dont know that, im still in highschool - My teacher only briefly mentioned sin cos and tang so i dont really know what its used for.
So what i have is
 ``1234567891011121314151617181920212223242526272829303132333435363738394041`` ``````if (kLeft) { if (KeyCounter >= KeyTick) { TankRotation -= 1; Redraw = true; KeyCounter = 0; } } if (kRight) { if (KeyCounter >= KeyTick) { TankRotation += 1; Redraw = true; KeyCounter = 0; } } if (kUp) { if (KeyCounter >= KeyTick) { TankX += (cos(ALLEGRO_PI/180 * TankRotation) * Speed); TankY += (sin(ALLEGRO_PI/180 * TankRotation) * Speed); Redraw = true; KeyCounter = 0; } } if (kDown) { if (KeyCounter >= KeyTick) { TankX += (cos(ALLEGRO_PI/180 * TankRotation)) * (Speed * -1); TankY += (sin(ALLEGRO_PI/180 * TankRotation)) * (Speed * -1); Redraw = true; KeyCounter = 0; } }``````

 `` `` `` al_draw_rotated_bitmap(Tank, 32, 32, TankX, TankY, TankRotation*(ALLEGRO_PI/180), NULL);``

But its still not working as expected, it rotates fine and smooth but it doesnt move as it should. Thanks for your help so far though.
And ehh i know globals are bad. Ill fix it right now
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