Sprites

Sprite is a computer graphics term for a two-dimensional bitmap that is integrated into a larger scene.

Originally sprites referred to independent objects that are composited together, by hardware, with other elements such as a background or tiles. The composition occurs as each scan line is prepared for the video output device, without involvement of the main CPU and without the need for a full-screen frame buffer. Sprites can be positioned or altered by setting attributes used during the hardware composition process.

Vicky is able to render 64 non-multiplexed sprites with a resolution of 32x32 pixels each. Just as bitmaps, a LUT is required for selecting 256 out of 16.777.216 colors.

NOTE: The upper left corner of the sprite is offset by 32 pixels. Using (0,0) will hide the sprite. Position (32,32) is mapped to the upper left corner of the screen.

Sprite Registers

Each Sprite has registers composed of a total of 8 bytes for manipulation, starting at $AF:0C00 and spanning through to $AF:0DFF.

The first set of sprite manipulation registers are shown below:

Attribute	Address
SP00_CONTROL_REG	= $AF:0C00
SP00_ADDY_PTR_L	= $AF:0C01
SP00_ADDY_PTR_M	= $AF:0C02
SP00_ADDY_PTR_H	= $AF:0C03
SP00_X_POS_L	= $AF:0C04
SP00_X_POS_H	= $AF:0C05
SP00_Y_POS_L	= $AF:0C06
SP00_Y_POS_H	= $AF:0C07

For each successive sprite, add +8 to the address registers.

The sprite control register (SPxy_CONTROL_REG) is always the first byte of the 8 byte block. The register is configured as follows:

Attribute	Bit
SPRITE_Enable	= $01
SPRITE_LUT0	= $02
SPRITE_LUT1	= $04
SPRITE_LUT2	= $08
SPRITE_DEPTH0	= $10
SPRITE_DEPTH1	= $20
SPRITE_DEPTH2	= $40
SPRITE_Collision_On	= $80