Add getting-started to part 2

src/SUMMARY.md

@@ -23,6 +23,7 @@
 
 # Part Ⅱ — Our first game
 
+- [Getting started](part2/getting-started.md)
 - [Work in progress](part2/wip.md)
 
 # Part Ⅲ — Our second game

src/part2/getting-started.md

@@ -0,0 +1,138 @@
+# Getting started
+
+In this lesson, we will start a new project from scratch.
+We will make a [Breakout](https://en.wikipedia.org/wiki/Breakout_%28video_game%29) / [Arkanoid](https://en.wikipedia.org/wiki/Arkanoid) clone, which we'll "Unbricked"!
+(Though you are free to give it any other name you like, as it will be *your* project)
+
+Open a terminal and make a new directory (`mkdir unbricked`), and then enter it (`cd unbricked`), just like you did for ["Hello, world!"](../part1/hello-world).
+
+Start by creating a file called `main.asm`, and include `hardware.inc` in your code.
+
+```
+line 1
+```
+
+`hardware.inc` is a file that provides constants which allow you to interface with the rest of the Game Boy.
+When you write code, your instructions are only read by the CPU.
+To access other parts of the system, like the screen, buttons, or audio, you use special registers known as "I/O" registers.
+These are different from the CPU registers in that they live within the address space, and are accessed through special numbers like `$FF40`.
+Numbers like this are difficult to memorize, and there are a *lot* to keep track of, which is why we use `hardware.inc` to assign them more freidnly names, like `rLCDC`.
+
+Next, make room for the header.
+[Remember from Part Ⅰ](../part1/header) that the header is where some information that the Game Boy relies on is stored, so you don't want to accidentally leave it out.
+
+```
+lines 3-7
+```
+
+The header jumps to `EntryPoint`, so let's write that now:
+
+```
+lines 9-18
+```
+
+The next few lines wait until "VBlank", which is the only time you can safely turn off the screen (doing so at the wrong time could damage a real Game Boy, so this is very crucial). We'll talk more about VBlank later.
+
+Turning off the screen is important because loading new tiles while the screen is on is tricky—we'll touch on how to do that in Part 3.
+
+Speaking of tiles, we're going to load some into VRAM next, using the following code:
+
+```
+lines 20-31
+```
+
+This loop might be [reminiscent of part Ⅰ](../part1/jumps#conditional-jumps).
+It copies `Tiles` to `$9000`, which is the part of VRAM where tiles are stored.
+To get how many bytes to copy, we will do just like in Part Ⅰ: using another label at the end, called `TilesEnd`, the difference between it (= the address after the last byte of tile data) and `Tiles` (= the address of the first byte) will be exactly that length.
+
+That said, we haven't written `Tiles` nor any of the related data yet.
+We'll get to that later!
+
+Almost done now—next, write another loop, this time for copying [the tilemap](../part1/tilemap).
+
+```
+lines 33-44
+```
+
+Note that while this loop's body is exactly the same as `CopyTiles`'s, the 3 values loaded into `de`, `hl`, and `bc` are different.
+These determine the source, destination, and size of the copy, respectively.
+
+::: tip DRY
+
+If you think that this is super redundant, you are not wrong, and we will see later how to write actual, reusable *functions*.
+But there is more to them than meets the eye, so we will start tackling them much later.
+
+:::
+
+Finally, let's turn the screen back on, and set a [background palette](../part1/palettes).
+Rather than writing the non-descript number `%10000001` (or $81 or 129, to taste), we make use of two constants graciously provided by `hardware.inc`: `LCDCF_ON` and `LCDCF_BGON`.
+When written to [`rLCDC`](https://gbdev.io/pandocs/LCDC), the former causes the PPU and screen to turn back on, and the latter enables the background to be drawn.
+(There are other elements that could be drawn, but we are not enabling them yet.)
+Combining these constants must be done using `|`, the *binary "or"* operator; we'll see why later.
+
+```
+lines 46-55
+```
+
+There's one last thing we need before we can build the ROM, and that's the graphics.
+We will draw the following screen:
+
+![Layout of unbricked](../assets/part2/tilemap.png)
+
+In `hello-world.asm`, tile data had been written out by hand in hexadecimal; this was to let you see how the sausage is made at the lowest level, but *boy* is it impractical to write!
+This time, we will employ a more friendly way, which will let us write each row of pixels more easily.
+We will use `dw` instead of `db` (the difference between these two will be explained later); and for each row of pixels, instead of writing [the bitplanes](../part1/tiles#encoding) as raw numbers, we will use a backtick (\`) followed by 8 characters.
+Each character defines a single pixel, intuitively from left to right; it must be one of 0, 1, 2, and 3, representing the corresponding color index in [the palette](../part1/palettes).
+
+::: tip
+
+0, 1, 2, and 3 aren't the only options for writing graphics.
+You can use [`OPT g`](https://rgbds.gbdev.io/docs/v0.5.2/rgbasm.5/#Changing_options_while_assembling) to modify these characters to your liking.
+
+:::
+
+For example:
+
+```rgbasm
+	dw `01230123 ; This is equivalent to `db $55,$33`
+```
+
+We already have tiles made for this project, so you can copy [this premade file](https://github.com/ISSOtm/gb-asm-tutorial-part2/raw/main/tileset.asm), and paste it at the end of your code.
+
+Then copy the tilemap from [this file](https://github.com/ISSOtm/gb-asm-tutorial-part2/raw/main/tilemap.asm), and paste it after the `TilesEnd` label.
+
+You can build the ROM now, by running the following commands in your terminal:
+
+```console
+$ rgbasm -L -o main.o main.asm
+$ rgblink -o unbricked.gb main.o
+$ rgbfix -v -p 0xFF unbricked.gb
+```
+
+If you run this in your emulator, you should see the following:
+
+(Screenshot pending :P)
+
+That white square seems to be missing!
+You may have noticed this comment earlier, somewhere in the tile data:
+
+```
+lines 135-140
+```
+
+The logo tiles were left intentionally blank so that you can choose your own.
+You can use one of the following pre-made logos, or try coming up with your own!
+
+## RGBDS Logo
+[Source](https://github.com/ISSOtm/gb-asm-tutorial-part2/raw/main/rgbds.asm)
+![The RGBDS Logo](https://github.com/ISSOtm/gb-asm-tutorial-part2/blob/main/rgbds.png?raw=true)
+
+## Duck
+[Source](https://github.com/ISSOtm/gb-asm-tutorial-part2/raw/main/duck.asm)
+![A pixel-art duck](https://github.com/ISSOtm/gb-asm-tutorial-part2/blob/main/duck.png?raw=true)
+
+## Tail
+[Source](https://github.com/ISSOtm/gb-asm-tutorial-part2/raw/main/tail.asm)
+![A silhouette of a tail](https://github.com/ISSOtm/gb-asm-tutorial-part2/blob/main/tail.png?raw=true)
+
+Replace the blank tiles with the new graphics, build the game again, and you should see your logo of choice in the bottom-right!