Moving object based on its rotation.

[veethree]

Hey. I need some help with a game i'm working on, nothing major, Just making it to kill time. But yeah, what i'm trying to do is make like a game where you're a space ship, and your goal is to shoot stuff and/or dodge obstacles. But what i can't figure out is how you would make an object (in this case a space ship thing) move forward based on its rotation. so when you would press the acceleration button it would go in the direction it's facing. I don't have a .love file for this or anything yet, since i'm not really sure where to start on this. Hope someone can help, I'd appreciate it. Thanks in advance.

[Nixola]

Your post reminded me sine, cosine and radians, but I don't know how to use them in LUA. However, something like your project is on my to-do list.

[CodeDemon]

Code: Select all

X=math.cos(Angle) * Speed
Y=math.sin(Angle) * Speed

X is the movement in the Horizontal direction, Y is the movement in the vertical direction, Angle is the angle of the obejct in radians and Speed is the amount of distance you wish the object to move.

[tentus]

Code: Select all

X=math.cos(Angle) * Speed
Y=math.sin(Angle) * Speed

X is the movement in the Horizontal direction, Y is the movement in the vertical direction, Angle is the angle of the obejct in radians and Speed is the amount of distance you wish the object to move.

A few quick changes to that:
- Be sure to add the result to the existing location.
- If you do the math in love.update() and multiply dt into the equation, your speed will be in pixels per second.
- Optionally, if you want your variables to work in degrees, you can convert degrees to radians using math.rad(Angle)

Code: Select all

function love.load()
   x = 100
   y = 100
   speed = 200   -- we move 200px per second
   angle = 180
end
function love.update(dt)
   x = x + (math.cos(math.rad(angle)) * speed * dt)
   y = y + (math.sin(math.rad(angle)) * speed * dt)
end

[fparedesg]

The following code creates a white ship in an 800x600 space. The ship is formed out of three triangles (the ship's three spikes).
dx: Horizontal position on the map, with 0 being the leftmost side and 800 being the rightmost side.
dy: Vertical position on the map, with 0 being the top side and 600 being the bottom side.
angle: Direction the ship is facing, with 0 being pointing right.

Right and left arrow keys rotate the ship. Right rotates clockwise and left rotates counterclockwise. (Right arrow decreases angle and left arrow increases angle).

Up/down arrows do not change neither dx nor dy. They increase velocity.x and velocity.y. Later, Movement(), which is run every time love.update(dt) is run, increases (or decreases) dx by velocity.x, and dy by velocity.y in every frame.

I have also included a Wrap() method that causes the frame's edges to wrap, so that the ship never exits the frame.

Code: Select all

function love.load()
	player =
		{
		dx = 400,
		dy = 300,
		velocity = {x = 0, y = 0},
		angle = 0
		}
	r = math.sqrt(450)
	
	--Arbitrary customizable variables. Feel free to modify.
	shipSize = 1
end

function love.draw()
	love.graphics.triangle("fill",
		10*shipSize*(math.cos(player.angle + 3*math.pi/2))+player.dx, -10*shipSize*(math.sin(player.angle + 3*math.pi/2))+player.dy,
		10*shipSize*(math.cos(player.angle + math.pi/2))+player.dx, -10*shipSize*(math.sin(player.angle + math.pi/2))+player.dy,
		30*shipSize*(math.cos(player.angle))+player.dx, -30*shipSize*(math.sin(player.angle))+player.dy)
	love.graphics.triangle("fill",
		0+player.dx, 0+player.dy,
		10*shipSize*(math.cos(player.angle + math.pi/2))+player.dx, -10*shipSize*(math.sin(player.angle + math.pi/2))+player.dy,
		r*shipSize*(math.cos(player.angle + 3*math.pi/4))+player.dx, -r*shipSize*(math.sin(player.angle + 3*math.pi/4))+player.dy)
	love.graphics.triangle("fill",
		0+player.dx, 0+player.dy,
		10*shipSize*(math.cos(player.angle + 3*math.pi/2))+player.dx, -10*shipSize*(math.sin(player.angle + 3*math.pi/2))+player.dy,
		r*shipSize*(math.cos(player.angle + 5*math.pi/4))+player.dx, -r*shipSize*(math.sin(player.angle + 5*math.pi/4))+player.dy)

	love.graphics.print("Ship Angle: " .. player.angle, 10, 0)
	love.graphics.print("cos(Angle): " .. math.cos(player.angle), 10, 10)
	love.graphics.print("sin(Angle): " .. math.sin(player.angle), 10, 20)
	love.graphics.print("shipSize: " .. shipSize, 10, 30)
	love.graphics.print("dx: " .. player.dx, 10, 40)
	love.graphics.print("dy: " .. player.dy, 10, 50)
	love.graphics.print("vx, vy: " .. player.velocity.x .. ", " .. player.velocity.y, 10, 60)
end

function love.update(dt)
	if love.keyboard.isDown("left") then
		player.angle = player.angle + dt
	end
	if love.keyboard.isDown("right") then
		player.angle = player.angle - dt
	end
	if love.keyboard.isDown("up") then
		player.velocity.x = player.velocity.x + 2*math.cos(player.angle)*dt
		player.velocity.y = player.velocity.y + 2*math.sin(player.angle)*dt
	end
	if love.keyboard.isDown("down") then
		player.velocity.x = player.velocity.x - 2*math.cos(player.angle)*dt
		player.velocity.y = player.velocity.y - 2*math.sin(player.angle)*dt
	end
	player.angle = player.angle%(2*math.pi)

	Wrap()
	Movement()
end

function Wrap()
	if player.dx > 820 then
		player.dx = player.dx - 840
	elseif player.dx < -20 then
		player.dx = player.dx + 840
	end

	if player.dy > 620 then
		player.dy = player.dy - 640
	elseif player.dy < -20 then
		player.dy = player.dy + 640
	end
end

function Movement()
	player.dx = player.dx + player.velocity.x
	player.dy = player.dy - player.velocity.y
end

Hope I made sense, I'm tired and English isn't my primary language.