Horizontal movement, acceleration, and max speed

Questions
#1

I’m having a lot of difficulty trying to get horizontal movement working the way I want it to work. Here’s my code:

if self.velocity.x == math.abs(self.velocity.x) then
	local speed1 = self.velocity.x + self.input.x * self.move_speed
	local speed2 = self.input.x * self.max_speed
	self.velocity.x = math.min(speed1, speed2)
else
	local speed1 = self.velocity.x + self.input.x * self.move_speed
	local speed2 = self.input.x * self.max_speed
	self.velocity.x = math.max(speed1, speed2)
end

if self.input.x == 0 then
	self.velocity.x = 0
end

Basically I want to be able to move left and right (controlled by the self.input vector) and then move up to max speed. Velocity should be set to 0 when both left and right keys are pressed, or when neither are pressed.

Right now the problem is that the velocity immediately rises to self.max_speed when moving left, but this code has gone through so many iterations over the past few days that I’m convinced there’s something fundamentally wrong with my approach.

How would you solve this problem?

#2

You’re not factoring in dt (Delta time). You’re doing this in update right?

#3

Yes. I’ve been testing this with and without delta time.

#4

Although it appears you are using whole integers when doing the calculations, I wonder if there might still be floating point issues.
In general, I’d advice against compares using “==”, since these are floating point numbers. Ofc, if it is guarantueed to be whole numbers, it should be ok.
You can read a bit more about floating point precision here.

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#5

If you are doing calculations in update() and don’t factor in delta time you will in a matter of frames (ie fractions of a second) end up at max speed.

I see that you’ve discarded the code from this post and I don’t really understand what you are doing with speed1 and speed2 in the snippet of code you shared. speed2 seems to be the be the horizontal max speed and speed1 is the current speed with movement factored in somehow.

BTW I created an example from the previous post where we discussed accelerating speed up to a max speed: https://defold.com/examples/basics/movement_speed/

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