# How to detect drawn shape

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What I am trying to do is let the player draw with his mouse for example and if he tries to draw a circle for example I can figure it out and replace the inaccurate shape of the player with the sprite of a perfect circle for example. I thought about using larp() and calculate the distance of each point to a point supposed center of the circle. If the distances are relatively close then it will be a circle. But I’m sure there is a better way to do this ? Thank you for your help

You can approach things two ways I think. The first thing is just to smooth out the line drawn by the user. I think there are multiple ways to do that, but I found this interesting article on the subject: Drawing smooth lines with cocos2d ios inspired by Paper

The other way, is to provide drawing tools, like circle, rectangle, etc… The user will draw what he thinks is a circle, and you can match it to the closest perfect circle.

I think these needs to be separate functions otherwise you could come into a situation where the user is drawing something, and your software thinks its close to a circle for example, so it matches it to a perfect circle and it’s not what the user wants.

MrEliptik | 2021-07-02 09:52

I’ve experimented with the same idea and managed few working examples

My thinking was…

CPU version:

1. prepared set of patterns:
• each pattern has same size (200x200px for ex.)
• pattern is collection of circles
1. while player draws you sample his strokes and scaled it to the same size as pattern images

2. compare given samples with predefined pattern → futher from the center of a point, the less accurate (you can set for example 5px radius)

3. … do a lot of optimalizations and thinking

GPU version:

1. prepared set of patterns are images with thick lines that fades from center to sides
• stronger color = more acurate to the pattern
1. player draws to texture as well