Creating vertices for a circle

Solar2D General Questions/Discussion
#1

Hey!

So, after reading another forum post, I realised that I might need to create a chain body for a circle in one of my projects at some point, so I decided to write a function for doing so and share it here.

Feel free to play around with the function and use it as you see fit. The function requires two inputs, r and n , where r stands for the circle radius and n stands for how many sides you want to create for the circle. The more sides, the more accurate the resulting circle will be. The function needs a minimum of 3 sides to work properly.

 

-- r = radius, n = number of sides local function circleVertices(r,n) if n \>= 3 then local mathCos, mathSin, pi = math.cos, math.sin, math.pi local angle = 360/n local v = {} for i = 1, n do v[i\*2-1] = mathCos(angle\*(i-1)\*(pi/180))\*r v[i\*2] = -1\*mathSin(angle\*(i-1)\*(pi/180))\*r end return v end end local t = circleVertices(120,32) local circle = display.newPolygon(240,160,t)

Finally, I’ve been thoroughly inspired by a few Corona developers, like roaminggamer and horacebury, who freely share numerous functions, modules and more on GitHub and I will very likely follow in suite and create myself a GitHub account and start sharing some more cool things with everyone. 

#2

@Xedur   I spent a long time combining physics bodies (usually four 2-D arcs) in order to make a hollow circle and then I discovered chain bodies which is essentially what I use for all landscapes and borders now.  Thanks for sharing with the community! 

#3

Yeah, when this is combined with the chain physics body, it’ll work just perfectly.

I’ve also opted to use chain bodies whenever possible because that way I don’t have to worry about the shapes being convex or consist of 8 vertices or less.

#4

Also I use a function similar to this and I feel good.

The only thing I noticed and that the rope in high speed cases could be less stable than a fixed body. In particular with very fast projectiles there are cases in which the strings are crossed.

But I repeat I talk about situations that are critical…

#5

fwiw, strength reduction:

local function regularPolygonVertices(r,n) assert(r~=0, "ERROR regularPolygonVertices(): a non-zero radius is required to form a valid polygon.") assert(n\>=3, "ERROR regularPolygonVertices(): at least three vertices are required to form a valid polygon.") local cos, sin = math.cos, math.sin local v, theta, dtheta = {}, 0, math.pi\*2/n for i = 1, n\*2, 2 do v[i] = r \* cos(theta) v[i+1] = r \* sin(theta) theta = theta + dtheta end return v end
#6

It really pays off to work on one’s functions for more than 5 minutes and perform proper optimisation. Thanks!

#7

Oh, by the way, does anyone have a clue if it is possible to dynamically create multi-element physics bodies?

To be precise, if I were to run the following code:
 

local physics = require("physics") physics.start() physics.setDrawMode( "hybrid" ) local function circleVertices(r,n) local cos, sin = math.cos, math.sin local v, theta, dtheta = {}, 0, math.pi\*2/n for i = 1, n\*2, 2 do v[i] = r \* cos(theta) v[i+1] = r \* sin(theta) theta = theta + dtheta end return v end local wallWidth = 16 local circleRadius = 120 local circleSides = 16 local innerT = circleVertices(circleRadius-wallWidth\*0.5,circleSides) local outerT = circleVertices(circleRadius+wallWidth\*0.5,circleSides) local collisionShape = {} for i = 1, circleSides do if i == circleSides then collisionShape[i] = { density=1.0, friction=1.0, bounce=0.2, shape={ innerT[i\*2-1], innerT[i\*2], innerT[1], innerT[2], outerT[1], outerT[2], outerT[i\*2-1], outerT[i\*2] }} else collisionShape[i] = { density=1.0, friction=1.0, bounce=0.2, shape={ innerT[i\*2-1], innerT[i\*2], innerT[i\*2+1], innerT[i\*2+2], outerT[i\*2+1], outerT[i\*2+2], outerT[i\*2-1], outerT[i\*2] }} end end local t = circleVertices(circleRadius,circleSides) local circle = display.newPolygon(240,160,t) circle:setFillColor(0.8,0,0) circle.strokeWidth = wallWidth physics.addBody( circle, "static", collisionShape[1], collisionShape[2], collisionShape[3], collisionShape[4], collisionShape[5], collisionShape[6], collisionShape[7], collisionShape[8], collisionShape[9], collisionShape[10], collisionShape[11], collisionShape[12], collisionShape[13], collisionShape[14], collisionShape[15], collisionShape[16] )

Then I end up with a rough circular shape that consists of 16 unique physics elements. However, for a circle of that size, 16 sides isn’t really enough to make it look like a real circle, but 32 sides should just about do it.

Is there a way to create a multi-element physics body during runtime so that I could avoid declaring each additional element individually like in the example?

#8

unpack(), fe read bottom of this

#9

Works like a charm! Thanks!
 

physics.addBody( circle, "static", unpack(collisionShape))
#10

@Xedur   I spent a long time combining physics bodies (usually four 2-D arcs) in order to make a hollow circle and then I discovered chain bodies which is essentially what I use for all landscapes and borders now.  Thanks for sharing with the community! 

#11

Yeah, when this is combined with the chain physics body, it’ll work just perfectly.

I’ve also opted to use chain bodies whenever possible because that way I don’t have to worry about the shapes being convex or consist of 8 vertices or less.

#12

Also I use a function similar to this and I feel good.

The only thing I noticed and that the rope in high speed cases could be less stable than a fixed body. In particular with very fast projectiles there are cases in which the strings are crossed.

But I repeat I talk about situations that are critical…

#13

fwiw, strength reduction:

local function regularPolygonVertices(r,n) assert(r~=0, "ERROR regularPolygonVertices(): a non-zero radius is required to form a valid polygon.") assert(n\>=3, "ERROR regularPolygonVertices(): at least three vertices are required to form a valid polygon.") local cos, sin = math.cos, math.sin local v, theta, dtheta = {}, 0, math.pi\*2/n for i = 1, n\*2, 2 do v[i] = r \* cos(theta) v[i+1] = r \* sin(theta) theta = theta + dtheta end return v end
#14

It really pays off to work on one’s functions for more than 5 minutes and perform proper optimisation. Thanks!

#15

Oh, by the way, does anyone have a clue if it is possible to dynamically create multi-element physics bodies?

To be precise, if I were to run the following code:
 

local physics = require("physics") physics.start() physics.setDrawMode( "hybrid" ) local function circleVertices(r,n) local cos, sin = math.cos, math.sin local v, theta, dtheta = {}, 0, math.pi\*2/n for i = 1, n\*2, 2 do v[i] = r \* cos(theta) v[i+1] = r \* sin(theta) theta = theta + dtheta end return v end local wallWidth = 16 local circleRadius = 120 local circleSides = 16 local innerT = circleVertices(circleRadius-wallWidth\*0.5,circleSides) local outerT = circleVertices(circleRadius+wallWidth\*0.5,circleSides) local collisionShape = {} for i = 1, circleSides do if i == circleSides then collisionShape[i] = { density=1.0, friction=1.0, bounce=0.2, shape={ innerT[i\*2-1], innerT[i\*2], innerT[1], innerT[2], outerT[1], outerT[2], outerT[i\*2-1], outerT[i\*2] }} else collisionShape[i] = { density=1.0, friction=1.0, bounce=0.2, shape={ innerT[i\*2-1], innerT[i\*2], innerT[i\*2+1], innerT[i\*2+2], outerT[i\*2+1], outerT[i\*2+2], outerT[i\*2-1], outerT[i\*2] }} end end local t = circleVertices(circleRadius,circleSides) local circle = display.newPolygon(240,160,t) circle:setFillColor(0.8,0,0) circle.strokeWidth = wallWidth physics.addBody( circle, "static", collisionShape[1], collisionShape[2], collisionShape[3], collisionShape[4], collisionShape[5], collisionShape[6], collisionShape[7], collisionShape[8], collisionShape[9], collisionShape[10], collisionShape[11], collisionShape[12], collisionShape[13], collisionShape[14], collisionShape[15], collisionShape[16] )

Then I end up with a rough circular shape that consists of 16 unique physics elements. However, for a circle of that size, 16 sides isn’t really enough to make it look like a real circle, but 32 sides should just about do it.

Is there a way to create a multi-element physics body during runtime so that I could avoid declaring each additional element individually like in the example?

#16

unpack(), fe read bottom of this

#17

Works like a charm! Thanks!
 

physics.addBody( circle, "static", unpack(collisionShape))