VDP Sprite API

Agon VDP sprite API

Currently there are 16 8bit commands to VDU 23, extension 27. These commands are structured in a way to not require any return values from the VDU.

Command structure

** Command (8bit) **	** Description **	** Parameters **	** Remarks **
bitmaps
0	Select bitmap	bitmap_id (8bit)	Subsequent bitmap commands are directed to selected bitmap id
1	Send bitmap data	width (16bit), height (16bit), pixel_array (32bit)	Allocates bitmap from VDU memory if necessary. Each pixel has 32bit color information in ABGR format
2	Define bitmap in single color	width (16bit), height (16bit), color(32bit)	Allocates bitmap from VDU memory if necessary. Color in ABGR format
3	Draw bitmap to screen	x (16bit), y (16bit)	Draws bitmap to screen
sprites
4	Select sprite	sprite_id (8bit)	Subsequent sprite commands are directed to selected sprite id
5	Clear frames	-	Clears out all frames from selected sprite. Do not clear sprites in activated range
6	Add frame to sprite	bitmap_id (8bit)	Adds first or next frame to sprite, based on bitmap_id. Fails silently if bitmap_id points to empty bitmap
7	Activate sprites	number (8bit)	Actives sprites 0-(number-1). Sprites need to have at least one frame added to them, else GDU crashes
8	Set next frame on sprite	-
9	Set previous frame on sprite	-
10	Set current frame id on sprite	frame_id (8bit)	frame_id needs to be 0 - framecount-1. Fails silently if outside this range, or if sprite is still empty.
11	Show sprite	-
12	Hide sprite	-
13	Move sprite to	x (16bit), y (16bit)	Move to absolute coordinates. Sprites are at (0,0) by default
14	Move sprite by offset	x (16bit), y (16bit)	Move to relative coordinates
15	Refresh all sprites

Example commands

• Select sprite 7 - transmit byte sequence 23,27,4,7
• Send bitmap data - transmit byte sequence 23,27,1,WidthLSB,WidthMSB,HeightLSB,HeightMSB, width x height x 4 byte of data
• Show sprite - transmit byte sequence 23,27,11

A proper sequence of events in creating bitmaps and/or sprites should be:

1. select a bitmap - Any number 0-255 will do
2. send one or more bitmaps data in ABGR format
3. select a sprite, starting with id 0
4. Potentially clear out old frames on this sprite, left by previous programs
5. add one or more frames to a sprite, using previously created bitmaps
6. Set sprite to show immediately on activation, hidden by default
7. Activate NUMBER of adjacent sprites (starting at 0) to the GDU
8. Refresh sprites, also after changes to position

Bitmaps can be drawn on the background canvas by using bitmap_draw(id), regardless of being (re)used by any sprites on the foreground.