Finding the corners of a part

Tweakified · July 26, 2021, 2:38pm

Hello,

I’m trying to make a spraycan that creates a decal once you click on the desired spot on your screen.
What I’m struggling with is verification to make sure the spot you’re placing the spraycan is a flat surface - otherwise it looks weird.

I thought of doing this via raycasting on each corner and seeing if the normal is the same.
At the moment I’m just trying to find the position of each corner and representing that with a part. Which is what is causing me trouble.
My current code (PartCFrame is the centre of the spraycan part):

local Centre = Instance.new("Part", workspace)
Centre.Size = Vector3.new(0.5, 0.5, 0.5)
Centre.Anchored = true
Centre.CFrame = PartCFrame

local TopRight = Instance.new("Part", workspace)
TopRight.CFrame = PartCFrame + Vector3.new(5.25, 0, 4.5)
TopRight.Size = Vector3.new(0.5, 0.5, 0.5)
TopRight.Anchored = true

local TopLeft = Instance.new("Part", workspace)
TopLeft.CFrame = PartCFrame + Vector3.new(5.25, 0, -4.5)
TopLeft.Size = Vector3.new(0.5, 0.5, 0.5)
TopLeft.Anchored = true

local BottomRight = Instance.new("Part", workspace)
BottomRight.CFrame = PartCFrame - Vector3.new(5.25, 0, 4.5)
BottomRight.Size = Vector3.new(0.5, 0.5, 0.5)
BottomRight.Anchored = true

local BottomLeft = Instance.new("Part", workspace)
BottomLeft.CFrame = PartCFrame - Vector3.new(5.25, 0, -4.5)
BottomLeft.Size = Vector3.new(0.5, 0.5, 0.5)
BottomLeft.Anchored = true

The spraycan part is 9, 10.5, 0.2 studs

My code results in this on a flat horizontal surface (works):
https://gyazo.com/bb946ba4cc266d06d113c577a4df1704

And this on a flat non horizontal surface (doesn’t work):
https://gyazo.com/83eca2cf35d5289d2b8dbe7ff521f59e
https://gyazo.com/2c00756c54dfa888a48937e06ccd0490

Any ideas/suggestions you have would be greatly appreciated,
Tweakified

CoderHusk · July 26, 2021, 3:19pm

god damn they need to make this an api already

github.com

FrostDracony/Roblox/blob/master/Tutorials/GetCornersOfAllBaseParts/GetCornersOfPart.md

# Get the Corners of a BasePart

## Table of Contents

* [Get the Corners of a normal Part](#get-the-corners-of-a-normal-part)
    * [Edit 1 We make our script shorter and more readable](#edit-1-we-make-our-script-shorter-and-more-readable)
    * [Edit 2 We use tables and the tipps of the replys](#edit-2-we-use-tables-and-the-tipps-of-the-replys)
	* [Edit3](#edit-3)

## Get the Corners of a normal Part
In this tutorial I will deal with getting the corners of a part. These can be used for many other things, for example to control a part into a certain region without using the function game.Workspace:FindPartInRegion3(). Let's start now. In this tutorial each corner is represented by a part which is 1x1x1. So you can see if the corner is really there where it should be. To get the corners of a non-rotating part you need a formula. For this it is better to paint a sketch. Here is what I painted (I'm not an artist so please no criticism):

![Sketch](imgs/GetCornersOfPart/Sketch.png)

In this sketch you can see how you can get all the corners of a normal part. The technique is to use vectors, just being able to read a bit, turn everything into vectors and there you have it!

The result is this:

![UnRotatedPart](imgs/GetCornersOfPart/UnRotatedPart.gif)

This file has been truncated. show original

Tweakified · July 26, 2021, 3:51pm

Thanks, that worked.
Here is how I modified that to work with my code:

local Centre = Instance.new("Part", workspace)
Centre.Size = Vector3.new(0.5, 0.5, 0.5)
Centre.Anchored = true
Centre.CFrame = PartCFrame

local TopRight = Instance.new("Part", workspace)
TopRight.CFrame = PartCFrame * CFrame.new(-4.5, 5.25, 0)
TopRight.Size = Vector3.new(0.5, 0.5, 0.5)
TopRight.Anchored = true

local TopLeft = Instance.new("Part", workspace)
TopLeft.CFrame = PartCFrame * CFrame.new(4.5, 5.25, 0)
TopLeft.Size = Vector3.new(0.5, 0.5, 0.5)
TopLeft.Anchored = true

local BottomRight = Instance.new("Part", workspace)
BottomRight.CFrame = PartCFrame * CFrame.new(-4.5, -5.25, 0)
BottomRight.Size = Vector3.new(0.5, 0.5, 0.5)
BottomRight.Anchored = true

local BottomLeft = Instance.new("Part", workspace)
BottomLeft.CFrame = PartCFrame * CFrame.new(4.5, -5.25, 0)
BottomLeft.Size = Vector3.new(0.5, 0.5, 0.5)
BottomLeft.Anchored = true