storing coordinates in a table

MoKaLux · April 2019

hello there, gideros people.

Can anybody tell me how to store coordinates in a table, please?

What I am trying to achieve:
I have a set of coordinates that I would like to use to draw a shape:

[[[79,39],[82,41],[84,48]],
[[84,48],[89,52],[90,59]],
[[70,29],[77,35],[79,39]],
[[66,67],[63,54],[66,50]],

I would like to store these coordinates in a table and draw the shape something like:

shape:lineTo(0, -40)
shape:lineTo(20, 0)
shape:lineTo(-20, 0)
shape:lineTo(0, -40)

But using a for loop:

for c = 1, #coords do
   shape:lineTo(coords[c].x, coords[c].y)
end

Any help would be appreciated. Thank you.

Apollo14 · April 2019

(sorry, maybe I didn't fully understand what you're trying to do)
Lua tables are very convenient.

local coords={}
 
coords[1]={x=0,y=100}
coords[2]={x=100,y=100}
coords[3]={x=100,y=0}
coords[4]={x=0,y=0}
 
square_shape:beginPath()
 
for c = 1, #coords do
   square_shape:lineTo(coords[c].x, coords[c].y)
end
 
square_shape:endPath()
 
--you can have lots of nested tables:
local otherCoordsTab={}
 
otherCoordsTab[1]={
   {79,39},{82,41},{84,48}
}
 
--to access it:
local num=otherCoordsTab[1,3,1]
print(num) --prints '84'

Useful info about original Lua tables construction syntax:
https://www.lua.org/pil/3.6.html
And info about enhanced table syntax in Gideros:
http://docs.giderosmobile.com/reference/enhancement/easyarray#Better and easier syntax for arrays

MoKaLux · April 2019

hi appolo14, thank you for your prompt reply.

That worked! What I did:

	-- shape
	local shape_points = {}
	table.insert(shape_points, {x=0, y=-40})
	table.insert(shape_points, {x=20, y=0})
	table.insert(shape_points, {x=-20, y=0})
	table.insert(shape_points, {x=0, y=-40})
 
	local shape = Shape.new()
	shape:setFillStyle(Shape.SOLID, 0xeeeeee)
	shape:setLineStyle(2, 0x001100, 1.0)
	shape:beginPath()
	shape:moveTo(0, 0)
 
	for p = 1, #shape_points do
		shape:lineTo(shape_points[p].x, shape_points[p].y)
	end
 
	shape:endPath()
 
	self:addChild(shape)

Thank you very much for your help. Do you think that is the right/best way of doing it?

Apollo14 · April 2019

MoKaLux said:
Do you think that is the right/best way of doing it?

I guess yes.
Perfomance-wise, 'table.insert(shape_points, {0,40}' is slower than 'shape_points[1]={0,40}'
(with 'table.insert' engine will have to pre-check what stuff is already there in table)

But you won't notice it unless you are filling lots of tables in one frame

MoKaLux · April 2019

Thank you apollo14.

SinisterSoft · April 2019

As above, but could be written as:

coords={{x=0,y=100},{x=100,y=100},{x=100,y=0},{x=0,y=0}}

or simply

coords={{0,100},{100,100},{100,0},{0,0}}

with coords[1][1] being 0 and [1][2] being 100

MoKaLux · April 2019

thank you sinistersoft.

oleg · April 2019

I do so:

			 coords.x= {
			{1,2,3,4,5},
			{1,2,3,4,5},
			{1,2,3,4,5},
			{1,2,3,4,5}
                          }
                        coords.y={
                          {1,2,3,4,5},
			{1,2,3,4,5},
			{1,2,3,4,5},
			{1,2,3,4,5}
                            }

or

coords={
{{79,39},{82,41},{84,48}},
{{84,48},{89,52},{90,59}},
{{70,29},{77,35},{79,39}},
{{66,67},{63,54},{66,50}}
}

MoKaLux · April 2019

yes, I did the latest! Thank you oleg.

antix · April 2019

I don't know how the code you have actually works correctly. In theory you need to move the cursor to the first coordinate and then loop from 2, #points.

Not doing so would draw a funny line from 0,0 to the first actual coordinate where you want to actually begin drawing from.

And with tables.. use table[#table + 1] = whatever to append to the end of a table quicker than table.insert. I suppose you could always use table[n] = whatever but I think table[#table + 1] = whatever is better

MoKaLux · April 2019

hello antix, that code worked because all my shapes are drawn from the 0, 0 origins. If the starting point is not at 0, 0 then I use moveto(x, y) and loop from 2, #points.

Ok, from now on when inserting things in tables I will use table[#table + 1] = whatever.

Thanks a lot all of you for your help and your precious advice.

I need more practice but I don't want to burn out!

antix · April 2019

@MoKaLux just incase you decide to start drawing from an origin other than 0,0 I'd suggest modifying the code now so it is more robust

and if you burn out.. don't worry.. it will only be for a little while.. and then you'll be right back at it!

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