In the last article, I referred to Playdate's official documentation, Inside Playdate, to successfully compile the source code from a sample open-sourced game on Github.
Now I'd like to become more familiar with the source code itself.
Of course, I want to start with something simple.
Thankfully, Inside Playdate features such an example.
Studying the example main.lua
file
This section of Inside Playdate features an example main.lua
file.
I intend to study it one line at a time.
import "CoreLibs/object"
import "CoreLibs/graphics"
import "CoreLibs/sprites"
import "CoreLibs/timer"
First are several core libraries. A library is a collection of code that makes doing something a lot easier than writing the code yourself.
local gfx <const> = playdate.graphics
Next is this local constant - a variable that cannot be reassigned. It's name is gfx
. The document states that this is just for convenience: writing three letters instead of 16 is always preferred.
local playerSprite = nil
Another local variable, starting value-less.
function myGameSetUp()
...
end
A function with a helpful name.
What's inside?
local playerImage = gfx.image.new("Images/playerImage")
A local variable.
I see now why the constant gfx
was a good idea.
But for full understanding, the expression is:
playdate.graphics.image.new("Images/playerImage")
So, stored in playerImage
is a literal image file located in the Images folder inside the source code's root directory.
assert( playerImage )
Using code to validate and confirm the contents of playerImage
.
playerSprite = gfx.sprite.new( playerImage )
Again, the long form is:
playdate.graphics.sprite.new(playerImage)
This creates a sprite from the image?
Interesting that it doesn't just use the image, but creates a sprite from it instead.
playerSprite:moveTo( 200, 120 )
The use of the colon is new syntax to me.
It seems like moveTo
is a method of playerSprite
.
I'm used to a period representing accessor syntax.
This moves the center of the sprite to 200,120 - the center of the screen.
playerSprite:add()
The comment in the documentation states This is critical!
.
It seems the sprite may not appear unless this method is invoked...even though the line above technically moved it to a spot on the screen?
local backgroundImage = gfx.image.new( "Images/background" )
assert( backgroundImage )
These two lines are identical - aside from variable and file names - to what's above for the playerImage
.
gfx.sprite.setBackgroundDrawingCallback(
function( x, y, width, height )
backgroundImage:draw( 0, 0 )
end
)
It's odd that sometimes a .
is used to access a method, and other times a :
is used. There must be some subtle difference that I'm missing in Lua.
Anyway, this function seems to expect a function as its first argument.
The expected function seems to expect four arguments.
Inside of it, the image is rendered at the top-left of the screen.
myGameSetUp()
The file invokes the custom function.
function playdate.update()
...
end
This function is a built-in event on the playdate.
I'm familiar with it from Pulp.
if playdate.buttonIsPressed( playdate.kButtonUp ) then
playerSprite:moveBy( 0, -2 )
end
if playdate.buttonIsPressed( playdate.kButtonRight ) then
playerSprite:moveBy( 2, 0 )
end
if playdate.buttonIsPressed( playdate.kButtonDown ) then
playerSprite:moveBy( 0, 2 )
end
if playdate.buttonIsPressed( playdate.kButtonLeft ) then
playerSprite:moveBy( -2, 0 )
end
In English:
If the current button pressed is one of the four d-pad buttons, then move the sprite by two pixels in the appropriate direction
I wonder why the button name is prefixed with a k
.
There's that :
again.
gfx.sprite.update()
playdate.timer.updateTimers()
Draw sprites and keep timers updated
More questions
- What's with the
.
and:
syntax? - Why the initial
k
in the button names? - Why sprites vs. images?
- What even is a sprite, technically?
- How would I make one so that I could try out this game?
It seems like I need to research sprites, next.
Top comments (0)