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GameBoy AdvanceProgramming
Tiles
Atari• 196?: As an engineering student at the University of Utah,
Nolan Bushnell liked to sneak into the computer labs late at night to play computer games on the university's $7 million mainframes.
• 1972: Bushnell founded Atari with $250 of his own money and another $250 from business partner Ted Dabney. They then created and commercialized the world's first commercial video game, Pong. Bushnell was 27 years old.
• 1976: Warner Communications buys Atari from Bushnell for $28 million.
• 1977: Atari introduces the Atari Video Computer System (VCS), later renamed the Atari 2600
• 1978: December - Atari announces the Atari 400 and 800 personal computers.
• 1979: October - Atari begins shipping the Atari 400 and Atari 800 personal computers.
Typical Atari 800 Screenshot
Atari Graphics
• Graphics and Text Modes
• Display List
• Customizable Fonts– Area in memory that described fonts
(characters)– Area in memory that was what went on screen
• Player/Missile Graphics
GBA Tiles
• Logical extension of the customizable character sets. Some of the terms used today are based on the historical derivation of the technology
• (The logical extension of the player/missile graphics is sprites)
Mode 3 Bitmaps
Video Processing Circuitry
Screen
Video Memory
What color to make a certain pixel
Mode 4 Bitmaps
Video Processing Circuitry
Screen
Video Memory
What color number to make a certain pixel
Palette Memory
What color is that?
Mode 0 Tilemaps
Video Processing Circuitry
Screen
Video Memory
What tile number to make a groupof pixels
Palette Memory
What color is that?
TileImages(Character Blocks)
What does that tile look like?
Tiles On Screen
30
20
Tiles & Tilemaps
• Tile– 8x8 bitmap image
• Treated like big pixels, as the building block of an image
– 16 or 256 colors– 32 or 64 bytes
• Tile Map– 2D array of tile indexes– Tile : Tilemap :: Pixel : Bitmap
Tradeoff
• 8 bpp = 256 colors– Lots of colors– All tiles share the same palette.– Tile images take more space
• 4 bpp = 16 palettes of 16 colors apiece– Still have 256 colors
• More constraints• More flexibility
– Tile images smaller (i.e. can have more)
Illustrations from Tonc
GBA Tile Mode Features
• Up to 4 tiled background layers– Up to 1024x1024 pixels each
• Hardware scrolling– Maps can be larger than the screen
• Hardware Parallax (optional)– Layers scroll at different speeds to simulate
depth
• Affine transformation (optional)– Rotation and scaling effects
Steps to Tiles
• Create tile images
• Create screen image
• Create a palette
• Store tile images in a character block
• Store screen image in one or more screen blocks
• Store palette in palette memory area
• Set image control buffer and Mode
Steps to Tiles
1. Create tile images
2. Create screen image
3. Create a palette
4. Store tile images in a character block
5. Store screen image in one or more screen blocks
6. Store palette in palette memory area
7. Set image control buffer and Mode
1&2&3. gfx2gba• Usagegfx2gba -fsrc -t8 -mm file.bmp
gfx2gba -fsrc -t8 -mm -c16 file.bmp
• -fsrc means produce c source files• -t8 means 8 bit tiles• -m Optimize tile images (remove duplicates, flip,
etc.• -c16 4bpp• file.bmp should be a 256 color (8bpp) image.• Add files to your project and extern them in your
other files.
1&2&3. usenti
4,5&6. Video Memory
CBB0 CBB1 CBB2 CBB3 CBB4 CBB5
4,5&6. Video Memory
CBB0 CBB1 CBB2 CBB3 CBB4 CBB5
Tile Palette: 0x5000000
4,5&6. Video Memory
CBB0 CBB1 CBB2 CBB3 CBB4 CBB5
Character Blocks 4 for tile images and maps 0x6000000
16kb 2kb
4,5&6. Video Memory
CBB0 CBB1 CBB2 CBB3 CBB4 CBB5
Tile Palette: 0x5000000
Character Blocks 4 for tile images and maps 0x6000000
16kb 2kb
4,5&6. Video Memory
CBB0 CBB1 CBB2 CBB3 CBB4 CBB5
0
1
2
3
4
0 0 0 00 2 3 02 1 1 34 4 4 4
Stop Here
Tile Size
• One 256 color tile has 8x8 8-bit indexes for a total of 64 bytes. One character block will hold 256 of these tile images.
• One 16 color tile has 8x8 4-bit indexes for a total of 32 bytes. One character block will hold 512 of these images
• Recall that there are 4 screen blocks but space for the tile map must be allocated.
Do the Math
• Suppose you had an image that was very complex?
Can we tile this image?
How big are things
• 16 color tiles are 32 bytes apiece
• 256 color tiles are 64 bytes apiece
Can we tile this image?
• Mode 3 video memory is 38400 shorts of 76800 bytes or 75KB
• In tile mode at 8bpp (same as Mode 4) we will use 38400 bytes
• In tile mode at 4 bpp we would use only 19200 bytes
• EXCEPT!!!!
Max Number of Tiles
• In the tile map 10 bits are allocated to identify which tile goes in each position
• 10 bits means we can only have 1024 unique tiles – We can actually make it look like more since
tiles can be flipped or be colored differently
• The screen is 20x30 tiles or 600 so we cannot tile an image that is > 1024 unique tiles!
Mode & BG Specifics
• Mode Backgrounds Rotation/Scaling
• 0 0, 1, 2, 3 No• 1 0, 1, 2 Yes (only background 2)
• 2 2, 3 YesBackground Resolution Rotation/Scaling• 0 512 x 512 No• 1 512 x 512 No• 2 128 to 1024 Yes• 3 128 to 1024 Yes
Background Layers
• 0 & 1– Max Resolution 512x512– Tile map of 16 bit numbers
• 2 & 3– Resolution from 128x128 to 1024x1024– Rotation & Scaling– Tile map of 8 bit numbers
Color
• 256 color tiles– 8 bits per pixel– Tiles share one 256 color palette
• 16 color tiles– 4 bits per pixel– Tiles use one of 16 palettes, 16 colors each– Note: Total palette is still 256 colors
Correct Incorrect: 256 color tiles being displayed as 16 color tiles
Tile Memory
• Double the sprite memory compared with bitmap modes
• Tile data video in video buffer– From 0x6000000 to 0x600FFFF– On 16k boundary (any of 4 spots)
• Tile map also stored in video buffer– On 2k boundary (any of 32 spots)
• Tile data and Tile map are in same space but normally would not overlap.
Video Memory
CBB0 CBB1 CBB2 CBB3 CBB4 CBB5
Tile Palette: 0x5000000
Character Blocks 4 for tile images and maps 0x6000000
16kb 2kb
Tile Data and Tile Map
• The tile map is stored in the same location as the video buffer (in the bitmap video modes), an array of numbers that point to the tile images.
• In text backgrounds (0 and 1) the tile map is
comprised of 16-bit numbers, while the rotation backgrounds (2 and 3) store 8-bit numbers in the tile map.
• When working with tile-based modes, video memory is divided into 4 logical char base blocks, which are made up of 32 smaller screen base blocks, as shown on the next slide.
Techniques
• Tile images must start at the beginning of a character block
• Tile maps must start at the beginning of a screen block
• How do we determine the correct address
• How do we do this in a C program?
4&5. Technique 1
• Calculate the address of each character block and each screen block and create a bunch of #defines for each one#define CHARACTERBLOCK0 0x6000000
#define CHARACTERBLOCK1 0x6004000
...
#define SCREENBLOCK0 0x6000000
#define SCREENBLOCK1 0x6000800
...
4&5. Technique 2
• Write macros to calculate the addresses#define CHARBLOCK(n) \
(unsigned short *) (0x6000000+(n)*0x4000)
#define SCREENBLOCK(n) \
(unsigned short *) (0x6000000+(n)*0x800)
4&5. Technique 3
• Let C do all the work!• Define structures: typedef struct { u16 tileimg[8192]; }
charblock;
typedef struct { u16 tilemap[1024]; }
screenblock;
• Define pointers charblock *charblockBase = (charblock *)0x6000000;
screenblock *screenblockBase =
(screenblock *)0x6000000;
4&5. Technique 3 Continued
• Now you can directly access the block you want using array indexing!!!!for(i=0; i<PicTileLen; i++){
charblockBase[1].tileimg[i] = picTile[i];
}
• What if i exceeds 8192???
6. Palette
• No different than Mode 4!
7. Control Registers
//background offset registers
#define REG_BG0HOFS *(volatile unsigned short *)0x04000010
#define REG_BG1HOFS *(volatile unsigned short *)0x04000014
#define REG_BG2HOFS *(volatile unsigned short *)0x04000018
#define REG_BG3HOFS *(volatile unsigned short *)0x0400001C
#define REG_BG0VOFS *(volatile unsigned short *)0x04000012
#define REG_BG1VOFS *(volatile unsigned short *)0x04000016
#define REG_BG2VOFS *(volatile unsigned short *)0x0400001A
#define REG_BG3VOFS *(volatile unsigned short *)0x0400001E
//background control registers
#define REG_BG0CNT *(volatile unsigned short*)0x4000008
#define REG_BG1CNT *(volatile unsigned short*)0x400000A
#define REG_BG2CNT *(volatile unsigned short*)0x400000C
#define REG_BG3CNT *(volatile unsigned short*)0x400000E
7. BGxCNT
bits name description
0-1 Pr Priority. Determines drawing order of backgrounds.
2-3 CBB Character Base Block. Sets the charblock that serves as the base
for character/tile indexing. Values: 0-3.
6 Mos Mosaic flag. Enables mosaic effect.
7 CM Color Mode. 16 colors (4bpp) if cleared; 256 colors (8bpp) if set.
8-12 SBB Screen Base Block. Sets the screenblock that serves as the base
for screen-entry/map indexing. Values: 0-31.
13 Wr Affine Wrapping flag. If set, affine background wrap around at their
edges. Has no effect on regular backgrounds as they wrap around
by default.
14-15 Sz Background Size. Regular and affine backgrounds have different
sizes available to them.
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
0F 0E 0D 0C 0B 0A 09 08 07 06 05 04 03 02 01 00
PrCBBMCMSBBWrSz
BGxCNT #defines
//macros and bit constants for setting the background control register specifics
#define SBB(num) num << 8
#define CBB(num) num << 2
#define COLOR256 1 << 7
// Cols x Row
#define BG_SIZE0 0<<14 // 32 x 32 tiles
#define BG_SIZE1 1<<14 // 64 x 32
#define BG_SIZE2 2<<14 // 32 x 64
#define BG_SIZE3 3<<14 // 64 x 64
Tile Maps
bits name description
0-9 TID Tile ID 0-511 (Thus maximum number of tiles per background is 512
10 HF Horizontal flip if set
11 VF Vertical flip if set
12-15 PB Palette bank in 4bpp (16 color) mode. Ignored in 8bpp (256 color)
mode
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
0F 0E 0D 0C 0B 0A 09 08 07 06 05 04 03 02 01 00
PB VF HF TID
Moving on a Big Map
What's your model?Screen Moves?
MAP
SCREEN
What's your model?
MAP
SCREEN
What's your model?
MAP
SCREEN
What's your model?
MAP
MAP
MAP
MAP
SCREEN
Or Map Moves?
MAP
SCREEN
What's your model?
MAP MAP
SCREEN
What's your model?
MAP MAP
SCREEN
What's your model?
MAP
MAPMAP
MAP
SCREEN
What's your model?
MAP
SCREEN
Either Works!
I like the screen moves
MAP
SCREEN
hoffvoff
The signs make more sense!
Use map coordinates
MAP
SCREEN
hoffvoff Row
Col
Where to draw it?
MAP
SCREEN
hoffvoff Row
Col
Screen coordinates for objectrowscreen = row -voffcolscreen = col -hoff
Questions?
Tile Setup//background setup registers and data#define REG_BG0CNT *(volatile unsigned short*)0x4000008#define REG_BG1CNT *(volatile unsigned short*)0x400000A#define REG_BG2CNT *(volatile unsigned short*)0x400000C#define REG_BG3CNT *(volatile unsigned short*)0x400000E#define BG_COLOR256 0x80#define CHAR_SHIFT 2#define SCREEN_SHIFT 8#define WRAPAROUND 0x1
//background tile bitmap sizes#define TEXTBG_SIZE_256x256 0x0#define TEXTBG_SIZE_256x512 0x8000#define TEXTBG_SIZE_512x256 0x4000#define TEXTBG_SIZE_512x512 0xC000
//background memory offset macros#define CharBaseBlock(n) (((n)*0x4000)+0x6000000)#define ScreenBaseBlock(n) (((n)*0x800)+0x6000000)
//background mode identifiers#define BG0_ENABLE 0x100#define BG1_ENABLE 0x200#define BG2_ENABLE 0x400#define BG3_ENABLE 0x800
Tile setup (cont)//video identifiers
#define REG_DISPCNT *(unsigned int*)0x4000000
#define BGPaletteMem ((unsigned short*)0x5000000)
#define SetMode(mode) REG_DISPCNT = (mode)
//vertical refresh register
#define REG_DISPSTAT *(volatile unsigned short*)0x4000004
//button identifiers
#define BUTTON_RIGHT 16
#define BUTTON_LEFT 32
#define BUTTON_UP 64
#define BUTTON_DOWN 128
#define BUTTONS (*(volatile unsigned int*)0x04000130)
Tile setup(cont)int main(void)
{
//create a pointer to background 0 tilemap buffer
unsigned short* bg0map =(unsigned short*)ScreenBaseBlock(31);
//set up background 0
REG_BG0CNT = BG_COLOR256 | TEXTBG_SIZE_256x256 | (31 << SCREEN_SHIFT) | WRAPAROUND;
//set video mode 0 with background 0
SetMode(0 | BG0_ENABLE);
//copy the palette into the background palette memory
DMAFastCopy((void*)test_Palette, (void*)BGPaletteMem, 256, DMA_16NOW);
//copy the tile images into the tile memory
DMAFastCopy((void*)test_Tiles, (void*)CharBaseBlock(0), 57984/4, DMA_32NOW);
//copy the tile map into background 0
DMAFastCopy((void*)test_Map, (void*)bg0map, 512, DMA_32NOW);
Input & Tile Scrolling
//main game loopwhile(1){ //wait for vertical refreshWaitVBlank();
//D-pad moves backgroundif(!(BUTTONS & BUTTON_LEFT)) x--;if(!(BUTTONS & BUTTON_RIGHT)) x++;if(!(BUTTONS & BUTTON_UP)) y--;if(!(BUTTONS & BUTTON_DOWN)) y++;
//use hardware background scrollingREG_BG0VOFS = y ;REG_BG0HOFS = x ;
//wait for vertical refreshWaitVBlank();
for(n = 0; n < 4000; n++);}return 0;}
Questions?
