Common coding tasks

[annikk.exe]

Figured I'd start a thread where I (and others) give examples of program code that is likely to be used often.

Let me know if you guys have any requests!
Also let me know if you spot a mistake, or you tried some of this code and it didn't work, even in an otherwise empty level file.

0. Contents

1. Send seedlings after a delay
2. Perform an arbitary number of different tasks after different amounts of time
3. Determine whether a number is odd or even
4. Calculate the distance between the centers of two asteroids
5. Calculate the distance between the closest edges of two asteroids
6. Calculate how much send distance is required for Asteroid 1 to be able to send seedlings to Asteroid 2
7. Calculate the X and Y coordinates at which the line formed by points: [Lx1, Ly1] [Lx2, Ly2] intersects with the line formed by [Lx3, Ly3] [Lx4, Ly4]
8. Calculate the X, Y and Z coordinates at which a line, denoted by any 2 points with coordinates [Lx1, Ly1, Lz1] [Lx2, Ly2, Lz2] intersects with a plane, denoted by any 3 coordinates on that plane; [Px1, Py1, Pz1] [Px2, Py2, Pz2] [Px3, Py3, Pz3]
9. Convert a set of 2D LevelDraw Coordinates into a set of 2D ScreenDraw Coordinates
10.  Concatenate one or more variables and/or one or more strings of text into a single MessageBox



1. Send seedlings after a delay

Code: [Select]

function LevelLogic()
-- create a "latch" variable, so that the seedlings are only sent once.
once = false


-- Run this loop continuously
while GameRunning() do

-- check if enough game time has passed yet
if GetGameTime() > 3 and once == false then

-- 3 seconds have passed - Asteroid 0 should now send 50 seedlings belonging to Empire 2 to Asteroid 1.
GetAsteroid(0):SendSeedlingsToTarget(50,2,GetAsteroid(1))

-- flip the latch
once = true

end

coroutine.yield()
end
end


2. Perform an arbitary number of different tasks after different amounts of time

Code: [Select]

function LevelLogic()
-- create an "incident" variable.  This will be used to store a note of which event is due to happen next.
incident = 0

-- create a "next" variable, this will record what the Game Time should be when the next incident must be run
next = 0

-- Run this loop continuously
while GameRunning() do

-- check if it's time for the next event
if GetGameTime() > next then

-- It's time, so run the action function for the current incident
Action(incident)

-- increment the incident counter by 1
incident = incident + 1

end

coroutine.yield()
end
end

function Action(incident)

if incident == 0 then
GetAsteroid(0):AddSeedlings(10)
next = GetGameTime() + 10
elseif incident == 1 then
GetAsteroid(0):AddSeedlings(20)
next = GetGameTime() + 5
elseif incident == 2 then
GetAsteroid(0):PlantDysonTree(1)
next = GetGameTime() + 25
elseif incident == 3 then
GetAsteroid(0):SendSeedlingsToTarget(50,1,GetAsteroid(1))
next = GetGameTime() + 10
elseif incident == 4 then
SetBackdropColour(0,0,80)
next = GetGameTime() + 15
else
-- no further incidents defined
end
end


3. Determine whether an integer is odd or even

Code: [Select]

if integer % 2 == 0 then -- if the integer divided by 2 has a remainder of 0, then
--the integer is even
else
-- the integer is odd
end

4. Calculate the distance between the centers of two asteroids

Code: [Select]

function LevelLogic()

-- first lets assign the values to some variables
roid1X = GetAsteroid(1).position.X
roid1Y = GetAsteroid(1).position.Y
roid2X = GetAsteroid(2).position.X
roid2Y = GetAsteroid(2).position.Y

-- next, calculate the diffence between their X coordinates
dx = roid2X - roid1X

-- and their Y coordinates
dy = roid2Y - roid1Y

-- dx and dy are like 2 sides of a right angled triangle.
-- If you recall pythagoras, the 3rd side (hypotenuse) can be calculated with a^2 + b^2 = c^2
-- So dx^2 + dy^2 = DistanceBetweenAsteroids^2

distance = math.sqrt((dx * dx) + (dy * dy))

end


5. Calculate the distance between the closest edges of two asteroids

Code: [Select]

function LevelLogic()

-- first lets assign the values to some variables
roid1X = GetAsteroid(1).position.X
roid1Y = GetAsteroid(1).position.Y
roid2X = GetAsteroid(2).position.X
roid2Y = GetAsteroid(2).position.Y

-- next, calculate the diffence between their X coordinates
dx = roid2X - roid1X

-- and their Y coordinates
dy = roid2Y - roid1Y

-- dx and dx are like 2 sides of a right angled triangle.
-- If you recall pythagoras, the 3rd side (hypotenuse) can be calculated with a^2 + b^2 = c^2
-- So dx^2 + dy^2 = DistanceBetweenAsteroids^2

dist = math.sqrt((dx * dx) + (dy * dy))

-- dist is the distance between the asteroid centers.  To get the actual distance between their surfaces, we must subtract both radii from dist
distance = dist - GetAsteroid(1).radius - GetAsteroid(2).radius

end

6. Calculate how much send distance is required for Asteroid 1 to be able to send seedlings to Asteroid 2

Code: [Select]

function LevelLogic()

-- first lets assign the values to some variables
roid1X = GetAsteroid(1).position.X
roid1Y = GetAsteroid(1).position.Y
roid2X = GetAsteroid(2).position.X
roid2Y = GetAsteroid(2).position.Y

-- next, calculate the diffence between their X coordinates
dx = roid2X - roid1X

-- and their Y coordinates
dy = roid2Y - roid1Y

-- dx and dx are like 2 sides of a right angled triangle.
-- If you recall pythagoras, the 3rd side (hypotenuse) can be calculated with a^2 + b^2 = c^2
-- So dx^2 + dy^2 = DistanceBetweenAsteroids^2

dist = math.sqrt((dx * dx) + (dy * dy))

-- dist is the distance between the asteroid centers.  To get the minimum required SendDistance, we measure from the center of Asteroid 1 (startpoint) to the edge of Asteroid 2 (destination)
distance = dist - GetAsteroid(2).radius

end

7. Calculate the X and Y coordinates at which the line formed by points: [Lx1, Ly1] [Lx2, Ly2] intersects with the line formed by [Lx3, Ly3] [Lx4, Ly4]

Code: [Select]

-- calculate A, B and C for both lines (standard form)
A1 = Ly2-Ly1
B1 = Lx1-Lx2
C1 = A1*x1+B1*y1
A2 = Ly4-Ly3
B2 = Lx3-Lx4
C2 = A3*x3+B3*y3

-- detect if they will ever intersect..
det = A1*B2 - A2*B1

if det == 0
--Lines are parallel

else
-- intersection coordinates give as:

intersectX = ((B2*C1) - (B1*C2)) / det
intersectY = ((A1*C2) - (A2*C1)) / det

end


8. Calculate the X, Y and Z coordinates at which a line, denoted by 2 points with coordinates [Lx1, Ly1, Lz1] [Lx2, Ly2, Lz2] intersects with a plane, denoted by 3 coordinates on that plane; [Px1, Py1, Pz1] [Px2, Py2, Pz2] [Px3, Py3, Pz3]

Code: [Select]

-- get 2 vectors along the plane
-- PV1x stands for Plane Vector #1, X-coordinate
PV1x = Px2 - Px1
PV1y = Py2 - Py1
PV1z = Pz2 - Pz1

PV2x = Px3 - Px1
PV2y = Py3 - Py1
PV2z = Pz3 - Pz1

-- now find the cross product, which is a line perpendicular to the plane
-- PV1 X PV2 = normal vector!
i = (PV1y * PV2z) - (PV1z * PV2y)
j = (PV1z * PV2x) - (PV1x * PV2z)
k = (PV1x * PV2y) - (PV1y * PV2x)

-- for the line, calculate tx, ty, tz
tx = Lx2 - Lx1
ty = Ly2 - Ly1
tz = Lz2 - Lz1

-- calculate t
num = ((i * (Px1 - Lx1)) + (j * (Py1 - Ly1)) + (k * (Pz1 - Lz1)))
denom = ((i * (Lx2 - Lx1)) + (j * (Ly2 - Ly1)) + (k * (Lz2 - Lz1)))
t = num / denom

-- calculate coordinates of the intersection point
intersectX = (t * tx) + Lx1
intersectY = (t * ty) + Ly1
intersectZ = (t * tz) + Lz1

9. Convert a set of 2D LevelDraw Coordinates into a set of 2D ScreenDraw Coordinates

Code: [Select]

-- where lvlX is the x-coordinate of the point in Leveldraw that must be converted, and lvlY is the y-coordinate.

screenX = (lvlX * GetCameraScale()) - (GetCameraX() * GetCameraScale()) + (GetScreenWidth() - (GetScreenWidth() / 2))
screenY = (lvly * GetCameraScale()) - (GetCameraY() * GetCameraScale()) + (GetScreenHeight() - (GetScreenHeight() / 2))

10.  Concatenate one or more variables and/or one or more strings of text into a single MessageBox

Code: [Select]

c1 = 5
d1 = 0
omg1 = "cats"

MessageBox(c1 .. d1)
-- "05"

MessageBox("Hello " .. omg1)
-- "Hello cats"

MessageBox("You have " .. c1 .. " " .. omg1 .. " and " .. d1 .. " dogs.  Clearly you must prefer " .. omg1 .. ".")
-- "You have 5 cats and 0 dogs.  Clearly you must prefer cats."

[annikk.exe]

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[annikk.exe]

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[Tomfloria]

Put in messages and while loops, if that's what it's called

[annikk.exe]

Hmm, do you need an example of just a while loop?
I would have thought they were covered adequately in the beginner and intermediate guides..

(especially the intermediate guide - there is a whole section that talks about while GameRunning() do at the start of it)

[annikk.exe]

And messagebox.... isn't MessageBox("Fish") self explanatory?

[annikk.exe]

I could do one on concatenating variables and text into the same MessageBox I suppose... that's not obvious.

[Tomfloria]

No I know how to do them XD, this is a common coding thread, I always use while loops

[Tomfloria]

Such as

Code: [Select]

while GetEmpire(0).NumSeedlings > 0 do --Checks to see if Empire 0's Number of Seedlings is 0 or less, can't be less than 0 though.

                        CheckConditions() --THIS IS SOMETHING I USE PERSONALLY. YOU DON'T NEED IT.

                        coroutine.yield() -- Makes this statement check over and over until Empire 0's number of seedlings is at 0
end --To end this statement

[annikk.exe]

By "common coding tasks" I mean the ones you are likely to have to do at some point, but excluding anything that is so basic that most people are likely to know about it already.

I'm also aiming to avoid duplicating anything in the beginner or intermediate guides.


I've added a concatenated messagebox guide.  :>

[Tomfloria]

OH.. ICUP.

[annikk.exe]

Also, I consider using any type of While loop other than While GameRunning() to be bad programming practice. :P

It's far far more flexible if you just have one loop running all the time, and then use conditionals to trigger code within that loop.  EG, did you see example 2 in this thread? :>

[Tomfloria]

I see what you mean, but isn't it easier to see your code in 1,2,3,4 (order) rather than somewhere else? At least easier for me

[annikk.exe]

It's slightly easier when you're doing basic things, but once you get into coding anything above beginner level, using any other kind of While loop other than while GameRunning() is likely to cause problems; you'll want to run multiple mechanics at once, but you won't be able to easily because different sections of code are looping at different times...


Hard to explain, but it's a conclusion I swiftly reached after I made the level "Return to Fluffy Land" which was my 2nd level ever.  I wrote that with lots of While loops that were triggered one after the other.  While 1 would loop for a while, then stop... then While 2 would loop for a while, then stop, then While 3 would loop...and so on.  It ended up being sooo messy, and by the end of the level I found it was restricting what I could do, so for the final loop I believe I just did While GameRunning() do, and then figured out how to run mechanics in parallel within that loop.

[annikk.exe]

The alternative to using lots of While loops, as I just described, is basically outlined in example 2.
If you set up a system like that, all the events that take place are grouped together, and adding a new event is very easy.  That's a way to create sequences of events after periods of time.  There are other ways to do it... like for example you could make events/incidents an array, and store the time they should be activated in each slot.  So for example incident[0] = 5 means that the first incident happens after 5 seconds of game time.  That would allow you to input specific times, rather than "15 seconds after the previous event".

Think of any functionality that you can do with lots of while loops, and I'll show you a way to do it better with while GameRunning()

:>