Change most uses of "sprite" to "object" (#484)

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

Author: pinobatch

src/Accessing_VRAM_and_OAM.md

@@ -4,7 +4,7 @@
 ::: warning Warning
 
 When the PPU is drawing the screen it is directly reading
-from Video Memory (VRAM) and from the Sprite Attribute Table (OAM).
+from Video Memory (VRAM) and from the Object Attribute Memory (OAM).
 During these periods the Game Boy CPU may not access VRAM and OAM.
 That means that any attempts to write to VRAM or OAM are ignored (data
 remains unchanged). And any attempts to read from VRAM or OAM will return

src/CGB_Registers.md

@@ -183,7 +183,7 @@ executed. During this time, the CPU is in a strange state. `DIV` does not tick,
 different results depending on the [STAT mode](<#STAT modes>) it's started in:
 
 - HBlank / VBlank (Mode 0 / Mode 1): The PPU cannot access any video memory, and produces black pixels
-- OAM scan (Mode 2): The PPU can access VRAM just fine, but not OAM, leading to rendering background, but not sprites
+- OAM scan (Mode 2): The PPU can access VRAM just fine, but not OAM, leading to rendering background, but not objects (sprites)
 - Rendering (Mode 3): The PPU can access everything correctly, and so rendering is not affected
 
 TODO: confirm whether interrupts can occur (just the joypad one?) during the pause, and consequences if so

src/GBC_Approval_Process.md

@@ -2,7 +2,8 @@
 
 Game Boy Color hardware applies automatic colorization to monochrome
 games, with one 4-color palette for backgrounds and two 3-color
-palettes for sprites.  Because of past under utilization of Super Game Boy
+palettes for objects (sprites).
+Because of past under-utilization of Super Game Boy
 features even in first-party games (as explained in an article by
 Christine Love), Nintendo required Game Boy Color games to appear
 more colorful than this automatic colorization. Thus, Nintendo

src/Interrupt_Sources.md

@@ -46,8 +46,8 @@ dynamically controlling the SCX/SCY registers ($FF43/$FF42) to [perform
 special video effects](https://github.com/gb-archive/DeadCScroll).
 
 Example application: set LYC to WY, enable LY=LYC interrupt, and have
-the handler disable sprites. This can be used if you use the window for
-a text box (at the bottom of the screen), and you want sprites to be
+the handler disable objects. This can be used if you use the window for
+a text box (at the bottom of the screen), and you want objects (sprites) to be
 hidden by the text box.
 
 ## INT $50 — Timer interrupt

src/LCDC.md

@@ -12,7 +12,7 @@ Bit | Name                           | Usage notes
  5  | Window enable                  | 0=Off, 1=On
  4  | BG and Window tile data area   | 0=8800-97FF, 1=8000-8FFF
  3  | BG tile map area               | 0=9800-9BFF, 1=9C00-9FFF
- 2  | OBJ size                       | 0=8x8, 1=8x16
+ 2  | OBJ size                       | 0=8×8, 1=8×16
  1  | OBJ enable                     | 0=Off, 1=On
  0  | BG and Window enable/priority  | 0=Off, 1=On
 
@@ -45,14 +45,14 @@ but the screen will stay blank during the first frame.
 ### LCDC.6 — Window tile map area
 
 This bit controls which background map the Window uses for rendering.
-When it's reset, the \$9800 tilemap is used, otherwise it's the \$9C00
+When it's clear (0), the \$9800 tilemap is used, otherwise it's the \$9C00
 one.
 
 ### LCDC.5 — Window enable
 
 This bit controls whether the window shall be displayed or not.
 This bit is overridden on DMG by [bit 0](<#LCDC.0 — BG and Window enable/priority>)
-if that bit is reset.
+if that bit is clear.
 
 Changing the value of this register mid-frame triggers a more complex behaviour:
 [see further below](<#FF4A–FF4B — WY, WX: Window Y position, X position plus 7>).
@@ -66,28 +66,30 @@ This bit controls which [addressing
 mode](<#VRAM Tile Data>) the BG and Window use to
 pick tiles.
 
-Sprites aren't affected by this, and will always use \$8000 addressing
-mode.
+Objects (sprites) aren't affected by this, and will always use the \$8000 addressing mode.
 
 ### LCDC.3 — BG tile map area
 
 This bit works similarly to [LCDC bit 6](<#LCDC.6 — Window tile map area>):
-if the bit is reset, the BG uses tilemap $9800, otherwise tilemap $9C00.
+if the bit is clear (0), the BG uses tilemap $9800, otherwise tilemap $9C00.
 
 
 ### LCDC.2 — OBJ size
 
-This bit controls the sprite size (1 tile or 2 stacked vertically).
+This bit controls the size of all objects (1 tile or 2 stacked vertically).
 
-Be cautious when changing this mid-frame from 8x8 to 8x16: "remnants"
-of the sprites intended for 8x8 could "leak" into the 8x16 zone and
+Be cautious when changing object size mid-frame.
+Changing from 8×8 to 8×16 pixels mid-frame within 8 scanlines of the bottom of an object
+causes the object's second tile to be visible for the rest of those 8 lines.
+If the size is changed during mode 2 or 3,
+remnants of objects in range could "leak" into the other tile and
 cause artifacts.
 
 ### LCDC.1 — OBJ enable
 
-This bit toggles whether sprites are displayed or not.
+This bit toggles whether objects are displayed or not.
 
-This can be toggled mid-frame, for example to avoid sprites being
+This can be toggled mid-frame, for example to avoid objects being
 displayed on top of a status bar or text box.
 
 (Note: toggling mid-scanline might have funky results on DMG?
@@ -101,13 +103,13 @@ LCDC.0 has different meanings depending on Game Boy type and Mode:
 
 When Bit 0 is cleared, both background and window become blank (white),
 and the [Window Display Bit](<#LCDC.5 — Window enable>)
-is ignored in that case. Only Sprites may still be displayed (if enabled
+is ignored in that case. Only objects may still be displayed (if enabled
 in Bit 1).
 
 #### CGB Mode: BG and Window master priority
 
 When Bit 0 is cleared, the background and window lose their priority -
-the sprites will be always displayed on top of background and window,
+the objects will be always displayed on top of background and window,
 independently of the priority flags in OAM and BG Map attributes.
 
 When Bit 0 is set, pixel priority is resolved [as described here](<#BG-to-OBJ Priority in CGB Mode>).
@@ -122,13 +124,13 @@ locks it. It's thus possible to modify it mid-scanline!
 
 ## Faux-layer textbox/status bar
 
-A problem often seen especially in NES games is sprites rendering on top
+A problem often seen in 8-bit games is objects rendering on top
 of the textbox/status bar. It's possible to prevent this using LCDC if
 the textbox/status bar is "alone" on its scanlines:
 
 -   Set LCDC.1 to 1 for gameplay scanlines
 -   Set LCDC.1 to 0 for textbox/status bar scanlines
 
 Usually, these bars are either at the top or bottom of the screen, so
-the bit can be set by the VBlank handler.
-
+the bit can be set by the VBlank and/or STAT handlers.
+Hiding objects behind a right-side window is more challenging.

src/Memory_Map.md

@@ -11,11 +11,11 @@ A000        | BFFF      | 8 KiB External RAM
 C000        | CFFF      | 4 KiB Work RAM (WRAM)                                            |
 D000        | DFFF      | 4 KiB Work RAM (WRAM)                                            | In CGB mode, switchable bank 1\~7
 E000        | FDFF      | Mirror of C000\~DDFF (ECHO RAM)                                  | Nintendo says use of this area is prohibited.
-FE00        | FE9F      | [Sprite attribute table (OAM)](<#VRAM Sprite Attribute Table (OAM)>) |
+FE00        | FE9F      | [Object attribute memory (OAM)](<#VRAM Sprite Attribute Table (OAM)>) |
 FEA0        | FEFF      | Not Usable                                                       | Nintendo says use of this area is prohibited
 FF00        | FF7F      | [I/O Registers](<#I/O Ranges>)                                   |
 FF80        | FFFE      | High RAM (HRAM)                                                  |
-FFFF        | FFFF      | [Interrupt](#Interrupts) Enable register (IE)                   |
+FFFF        | FFFF      | [Interrupt](#Interrupts) Enable register (IE)                    |
 
 ## Jump Vectors in first ROM bank
 

src/OAM.md

@@ -1,47 +1,51 @@
 
-# VRAM Sprite Attribute Table (OAM)
+# Object Attribute Memory (OAM)
 
-The Game Boy PPU can display up to 40 sprites either in 8x8 or
-in 8x16 pixels. Because of a limitation of hardware, only ten sprites
-can be displayed per scan line. Sprite tiles have the same format as
-BG tiles, but they are taken from the Sprite Tiles Table located at
+The Game Boy PPU can display up to 40 movable objects (or sprites), each 8×8 or
+8×16 pixels. Because of a limitation of hardware, only ten objects
+can be displayed per scanline. Object tiles have the same format as
+BG tiles, but they are taken from tile blocks 0 and 1 located at
 $8000-8FFF and have unsigned numbering.
 
-Sprite attributes reside in the Sprite Attribute Table (OAM: Object
-Attribute Memory) at \$FE00-FE9F. Each of the 40 entries consists of
+Object attributes reside in the object attribute memory (OAM) at \$FE00-FE9F.
+(This corresponds to the sprite attribute table on a TMS9918 VDP.)
+Each of the 40 entries consists of
 four bytes with the following meanings:
 
 ## Byte 0 — Y Position
 
-Y = Sprite's vertical position on the screen + 16. So for example,
-Y=0 hides a sprite,
-Y=2 hides an 8×8 sprite but displays the last two rows of an 8×16 sprite,
-Y=16 displays a sprite at the top of the screen,
-Y=144 displays an 8×16 sprite aligned with the bottom of the screen,
-Y=152 displays an 8×8 sprite aligned with the bottom of the screen,
-Y=154 displays the first six rows of a sprite at the bottom of the screen,
-Y=160 hides a sprite.
+![Interpretation of object Y coordinates](imgs/Objects_vertical_position.png)
+
+Y = Object's vertical position on the screen + 16. So for example:
+
+- Y=0 hides an object,
+- Y=2 hides an 8×8 object but displays the last two rows of an 8×16 object,
+- Y=16 displays an object at the top of the screen,
+- Y=144 displays an 8×16 object aligned with the bottom of the screen,
+- Y=152 displays an 8×8 object aligned with the bottom of the screen,
+- Y=154 displays the first six rows of an object at the bottom of the screen,
+- Y=160 hides an object.
 
 ## Byte 1 — X Position
 
-X = Sprite's horizontal position on the screen + 8. This works similarly
-to the examples above, except that the width of a sprite is always 8. An
-off-screen value (X=0 or X\>=168) hides the sprite, but the sprite still
-affects the priority ordering, thus other sprites with lower priority may be
-left out due to the ten sprites limit per scan-line.
-A better way to hide a sprite is to set its Y-coordinate off-screen.
+X = Object's horizontal position on the screen + 8. This works similarly
+to the examples above, except that the width of an object is always 8. An
+off-screen value (X=0 or X\>=168) hides the object, but the object still
+contributes to the limit of ten objects per scanline.
+This can cause objects later in OAM not to be drawn on that line.
+A better way to hide an object is to set its Y-coordinate off-screen.
 
 ## Byte 2 — Tile Index
 
-In 8x8 mode (LCDC bit 2 = 0), this byte specifies the sprite's only tile index ($00-$FF).
-This unsigned value selects a tile from the memory area at $8000-$8FFF.
+In 8×8 mode (LCDC bit 2 = 0), this byte specifies the object's only tile index (\$00-\$FF).
+This unsigned value selects a tile from the memory area at \$8000-\$8FFF.
 In CGB Mode this could be either in
 VRAM bank 0 or 1, depending on bit 3 of the following byte.
-In 8x16 mode (LCDC bit 2 = 1), the memory area at $8000-$8FFF is still interpreted
-as a series of 8x8 tiles, where every 2 tiles form a sprite. In this mode, this byte
-specifies the index of the first (top) tile of the sprite. This is enforced by the
-hardware: the least significant bit of the tile index is ignored; that is, the top 8x8
-tile is "NN & $FE", and the bottom 8x8 tile is "NN | $01".
+In 8×16 mode (LCDC bit 2 = 1), the memory area at \$8000-\$8FFF is still interpreted
+as a series of 8×8 tiles, where every 2 tiles form an object. In this mode, this byte
+specifies the index of the first (top) tile of the object. This is enforced by the
+hardware: the least significant bit of the tile index is ignored; that is, the top 8×8
+tile is "NN & \$FE", and the bottom 8×8 tile is "NN | \$01".
 
 ## Byte 3 — Attributes/Flags
 
@@ -87,7 +91,7 @@ limit, possibly causing another object later in OAM not
 to be drawn. To keep off-screen objects from affecting on-screen ones, make
 sure to set their Y coordinate to Y = 0 or Y ≥ 160
 (144 + 16).
-(Y&nbsp;≤&nbsp;8 also works if [object size](<#LCDC.2 — OBJ size>) is set to 8x8.)
+(Y&nbsp;≤&nbsp;8 also works if [object size](<#LCDC.2 — OBJ size>) is set to 8×8.)
 
 ### Drawing priority
 

src/OAM_Corruption_Bug.md

@@ -1,7 +1,7 @@
 # OAM Corruption Bug
 
 There is a flaw in the Game Boy hardware that causes rubbish data to be written
-to OAM RAM if the following instructions are used while their 16-bit content
+to object attribute memory (OAM) if the following instructions are used while their 16-bit content
 (before the operation) is in the range $FE00–$FEFF and the PPU is in mode 2:
 
 ```rgbasm
@@ -10,7 +10,7 @@ to OAM RAM if the following instructions are used while their 16-bit content
  ld [hli], a    ld [hld], a
 ```
 
-Sprites 1 & 2 ($FE00 & $FE04) are not affected by this bug.
+Objects 0 and 1 ($FE00 & $FE04) are not affected by this bug.
 
 Game Boy Color and Advance are not affected by this bug, even when
 running monochrome software.
@@ -20,11 +20,14 @@ running monochrome software.
 The OAM Corruption Bug (or OAM Bug) actually consists of two different bugs:
 
 - Attempting to read or write from OAM (Including the $FEA0-$FEFF
-  region) while the PPU is in mode 2 (OAM mode) will corrupt it.
+  region) while the PPU is in mode 2 (OAM scan) will corrupt it.
 - Performing an increase or decrease operation on any 16-bit register
   (BC, DE, HL, SP or PC) while that register is in the OAM range
-  ($FE00 - $FEFF) will trigger a memory write to OAM, causing a
-  corruption.
+  ($FE00–$FEFF) will trigger an access to OAM, causing a corruption.
+  This happens because the CPU's increment and decrement unit (IDU)
+  for 16-bit numbers is directly tied to the address bus.
+  During IDU operation, the value is output as an address,
+  even if a read or write is not asserted.
 
 ## Affected Operations
 
@@ -66,7 +69,7 @@ operations are on 16-bit words.
 
 A "write corruption" corrupts the currently access row in the following
 manner, as long as it's not the first row (containing the first two
-sprites):
+objects):
 
 - The first word in the row is replaced with this bitwise expression:
   `((a ^ c) & (b ^ c)) ^ c`, where `a` is the original value of that

src/Rendering.md

@@ -16,14 +16,14 @@ and some others to higher abstractions concepts.
 
 Similarly to other retro systems, pixels are not manipulated
 individually, as this would be expensive CPU-wise. Instead, pixels are grouped
-in 8x8 squares, called _tiles_ (or sometimes "patterns"), often considered as
+in 8x8 squares, called _tiles_ (or sometimes "patterns" or "characters"), often considered as
 the base unit in Game Boy graphics.
 
 A tile does not encode color information. Instead, a tile assigns a
 _color ID_ to each of its pixels, ranging from 0 to 3. For this reason,
 Game Boy graphics are also called _2bpp_ (2 bits per pixel). When a tile is used
 in the Background or Window, these color IDs are associated with a _palette_. When
-a tile is used in an OBJ, the IDs 1 to 3 are associated with a palette, but
+a tile is used in an object, the IDs 1 to 3 are associated with a palette, but
 ID 0 means transparent.
 
 ## Palettes
@@ -59,7 +59,7 @@ It is fairly limited: it has no transparency, it's always a
 rectangle and only the position of the top-left pixel can be controlled.
 
 Possible usage include a fixed status bar in an otherwise scrolling game (e.g.
-_Super Mario Bros. 3_).
+_Super Mario Land 2_).
 
 ### Objects
 
@@ -82,4 +82,4 @@ To summarise:
 
 - **Tile**, an 8x8-pixel chunk of graphics.
 - **Object**, an entry in object attribute memory, composed of 1 or 2
-  tiles. Independent of the background.
+  tiles. Can be moved independently of the background.