Part II, Lesson 5 (#46)

Co-authored-by: Eldred Habert <eldredhabert0@gmail.com>
Co-authored-by: Antonio Vivace <avivace4@gmail.com>

Author: 3 people

src/SUMMARY.md

@@ -28,6 +28,7 @@
 - [Functions](part2/functions.md)
 - [Input](part2/input.md)
 - [Collision](part2/collision.md)
+- [Bricks](part2/bricks.md)
 - [Work in progress](part2/wip.md)
 
 # Part Ⅲ — Our second game

src/part2/bricks.md

@@ -0,0 +1,97 @@
+# Bricks
+
+Up until this point our ball hasn't done anything but bounce around, but now we're going to make it destroy the bricks.
+
+Before we start, let's go over a new concept: constants.
+We've already used some constants, like `rLCDC` from `hardware.inc`, but we can also create our own for anything we want.
+Let's make three constants at the top of our file, representing the tile IDs of left bricks, right bricks, and blank tiles.
+```rgbasm,linenos,start={{#line_no_of "" ../../unbricked/bricks/main.asm:constants}}
+{{#include ../../unbricked/bricks/main.asm:constants}}
+```
+
+Constants are a kind of *symbol* (which is to say, "a thing with a name").
+Writing a constant's name in an expression is equivalent to writing the number the constant is equal to, so `ld a, BRICK_LEFT` is the same as `ld a, $05`.
+But I think we can all agree that the former is much clearer, right?
+
+## Destroying bricks
+
+Now we'll write a function that checks for and destroys bricks.
+Our bricks are two tiles wide, so when we hit one we'll have to remove the adjacent tile as well.
+If we hit the left side of a brick (represented by `BRICK_LEFT`), we need to remove it and the tile to its right (which should be the right side).
+If we instead hit the right side, we need to remove the left!
+
+```rgbasm,linenos,start={{#line_no_of "" ../../unbricked/bricks/main.asm:check-for-brick}}
+{{#include ../../unbricked/bricks/main.asm:check-for-brick}}
+```
+
+Just insert this function into each of your bounce checks now.
+Make sure you don't miss any!
+It should go right **before** the momentum is modified.
+
+```diff,linenos,start={{#line_no_of "" ../../unbricked/bricks/main.asm:updated-bounce}}
+BounceOnTop:
+	; Remember to offset the OAM position!
+	; (8, 16) in OAM coordinates is (0, 0) on the screen.
+	ld a, [_OAMRAM + 4]
+	sub a, 16 + 1
+	ld c, a
+	ld a, [_OAMRAM + 5]
+	sub a, 8
+	ld b, a
+	call GetTileByPixel ; Returns tile address in hl
+	ld a, [hl]
+	call IsWallTile
+	jp nz, BounceOnRight
++	call CheckAndHandleBrick
+	ld a, 1
+	ld [wBallMomentumY], a
+
+BounceOnRight:
+	ld a, [_OAMRAM + 4]
+	sub a, 16
+	ld c, a
+	ld a, [_OAMRAM + 5]
+	sub a, 8 - 1
+	ld b, a
+	call GetTileByPixel
+	ld a, [hl]
+	call IsWallTile
+	jp nz, BounceOnLeft
++	call CheckAndHandleBrick
+	ld a, -1
+	ld [wBallMomentumX], a
+
+BounceOnLeft:
+	ld a, [_OAMRAM + 4]
+	sub a, 16
+	ld c, a
+	ld a, [_OAMRAM + 5]
+	sub a, 8 + 1
+	ld b, a
+	call GetTileByPixel
+	ld a, [hl]
+	call IsWallTile
+	jp nz, BounceOnBottom
++	call CheckAndHandleBrick
+	ld a, 1
+	ld [wBallMomentumX], a
+
+BounceOnBottom:
+	ld a, [_OAMRAM + 4]
+	sub a, 16 - 1
+	ld c, a
+	ld a, [_OAMRAM + 5]
+	sub a, 8
+	ld b, a
+	call GetTileByPixel
+	ld a, [hl]
+	call IsWallTile
+	jp nz, BounceDone
++	call CheckAndHandleBrick
+	ld a, -1
+	ld [wBallMomentumY], a
+BounceDone:
+```
+
+That's it!
+Pretty simple, right?