# Smoother player sprite movement?

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Hey everyone, so first post here though have been reading these forums for a while now. Anyways to my question. I am currently undertaking a little game to learn more about Python and (Pyglet/Cocos2D) for game development. It is going to be a simple vertical space shooter arcade game. It is going quite well and I am pleasantly surprised at how well Python handles stuff but I have run into a minor problem.

Currently I am handling my player movement with the mouse. When the mouse moves the player ship moves around the screen. Though when looking at it, it seems like when the ship is moving around the screen it is very "jerky" and the movement isn't very smooth like you see in most space shooters. I am struggling to figure out a way to fix this.

The way I am handling moving the sprite is with Pyglets on_mouse_motion function.

def on_mouse_motion(x, y, dx, dy):

X and Y are not used here since I have set mouse mouse exclusivity to my game window. So I am using dx and dy which sends how many pixels the mouse and moved since the last frame (Or however it samples it). So it basically looks something like this.

def on_mouse_motion(self, x, y, dx, dy):
# Player is a created class that is inherited from pyglet.sprite.Sprite
# moveSpeed I believe is set to 0.15 or something around there
player.x += dx * player.moveSpeed
player.y += dy * player.moveSpeed

I hope I'm not doing anything to stupid, because the movement is a bit jerky and not very smooth. So I was hoping maybe you guys had some ideas on what I could do to make the movement look better. Maybe use a animation for my player's sprite (I am using a single image right now)? Or I have seen some games create a fading trail behind the player ship, maybe this is to mask this jerky movement? I really don't know and am a bit of a loss on how to fix this (Math is definitively not my strong suit).

So any help would appreciated and thank you in advance. Also if you need any more source code or even the whole projects code just let me know. I would have attached it know but am at work and don't have access to it at the moment so just went off memory. And replies don't have to be in Python I am just using that because I am currently studying it but I can also implement any suggested fixes in C/C++ also.

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I've no concrete snippet at hand, just an advice:

Animation doesn't change the jerkiness of motion. Look at the positions as being samples of a motion path. Compute a sufficiently smooth path (e.g. quadratic interpolation, better yet use an approximation), and re-sample it accordingly to distances moved along the path in the time duration since the last recent rendering.

Edited by haegarr

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Ahh I believe I get what you are saying. Basically I should be doing something like this (Correct me if I am wrong)

player.x += dx * deltaTime
player.y += dy * deltaTime

If I am understanding the Pyglet library correctly and the concept, the dx and dy parameters hold how far the mouse has moved along the x and y axis I then multiply it by deltaTime which is how much time has past since the last frame update?

At least that is what I believe you are saying (Again I know almost no advanced maths, though I am trying to work on that).

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If I correctly understand what you're trying to accomplish here, you need to normalize dx and dy to represent a unit vector so they don't influence your playerspeed.

Normalizing can be accomplished by computing the length of the vector dx, dy represents, ie length = sqrt(dx*dx + dy*dy), then dividing both dx and dy by this length:

dx /= length

dy /= length

I am not familiar with python, so some of that syntax may be incorrect.

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the only idea I have is to use acceleration and velocity. Let the mouse movements determine where the desired position is, then code, use a motion profile (acc/vel) to change position. you'll get a 'spring' effect.  Tight coupling (between things like user input and position or velocity) leads to rough movement unless the code is really tight.

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the only idea I have is to use acceleration and velocity. Let the mouse movements determine where the desired position is, then code, use a motion profile (acc/vel) to change position. you'll get a 'spring' effect.  Tight coupling (between things like user input and position or velocity) leads to rough movement unless the code is really tight.

Thank you for the suggestion. I might actually do that, because when I was making my asteroids clone I used basic acc/vel and the movement was much smoother then what I have in my current project. So think I will hold off of other types of movements and stick to acceleration and velocity until I get a better handle on the concepts behind everything.

Thanks again everyone.

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