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.

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

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.