VDP Sprites

Display Capacity

H32 mode

In H32 mode the VDP can display up to 64 sprites per frame.

There is some limitation on a line basis.

A maximum of 16 sprites and a maximum of 256 pixels will be displayed on each lines.

The displayed sprites/pixels are the one with the highest priority.

H40 mode

In H40 mode the VDP can display up to 80 sprites per frame.

There is some limitation on a line basis.

A maximum of 20 sprites and a maximum of 320 pixels will be displayed on each lines.

The displayed sprites/pixels are the one with the highest priority.

Display Position

The sprite position defined where to start drawing the sprite from the top-left corner.

Horizontal

The sprite H position is between 0 and 511 but the display area is from 128 to 383 in H32 mode and 128 to 447 in H40 mode.

When the sprite H position is 0 this is a special mode. All the sprites on the same line with low priority will not be displayed.

Vertical Non-interlace

The sprite V position is between 0 and 511 but the display area is from 128 to 351 in V28 mode and 128 to 367 in V30 mode.

Vertical Interlace mode 2

The sprite V position is between 0 and 1024 but the display area is from 256 to 703 in V28 mode and 256 to 735 in V30 mode.

Attribute Table

The Sprite attribute table address is defined via the vdp register 0x5.

Each sprites require 4 words.

0	Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Def Unused Vertical Position
1	Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Def Unused Horizontal size Vertical size Unused Link
2	Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Def Priority Palette ID Vertical Reverse Horizontal Reverse Tile ID
3	Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Def Unused Horizontal Position

Size

16 different sprite size are selectable

The relationship between the tile id and the placement follow a top-left to bottom-right order.

	V = 0	V = 1	V = 2	V = 3
H = 0	0	0 1	0 1 2	0 1 2 3
H = 1	0 1	0 2 1 3	0 3 1 4 2 5	0 4 1 5 2 6 3 7
H = 2	0 1 2	0 2 4 1 3 5	0 3 6 1 4 7 2 5 8	0 4 8 1 5 9 2 6 A 3 7 B
H = 3	0 1 2 3	0 2 4 6 1 3 5 7	0 3 6 9 1 4 7 A 2 5 8 B	0 4 8 C 1 5 9 D 2 6 A E 3 7 B F

Link / Priority

Each sprites entry in the attribute table have a link property.

This indicated the sprites ID to draw next.

The VDP always starts by the sprites 0 and then follows the link data. The list must be closed by relinking to the sprites 0. (What happens if not ???)

Sprite 0 have priority 1, next one priority 2 etc ....