SPC8106 S-MOS Systems, SPC8106 Datasheet - Page 364

• Manufacturer Part Number: SPC8106
• Description: LCD/CRT VGA CONTROLLER
• Manufacturer: S-MOS Systems

1.1
The displayed position of the sprite and any required clipping is done with CRTC registers 30h
through 35h. Clipping of the sprite image on the right and bottom of the display is done automati-
cally by the hardware. If the sprite image needs to be clipped on the top or left of the display the
clipped amount needs to be calculated and set into the appropriate registers.
All position calculations are based on absolute pixel positions. This holds even for text modes,
which means the sprite image location is not limited to character cell boundaries, but may be
placed on any pixel on the display. Sprite positioning information is always relative to the upper
left corner of the sprite image and to the upper left corner of the display. The following example
demonstrates how to program a cursor image located in the lower left qaudrant of the sprite as
this covers all positioning considerations.
In general the algorithm for cursor position and clipping is:
The following example is typical of the logic to program a cursor position with coordinates passed
by Microsoft Windows.
Programming the Sprite Hardware
UY16-8
/* Calculate the Xposition and Xstart. */
CursorX = CursorPos - HotSpot // nCursorX = raw X position
if (CursorX > 0) {
else {
/* Now program the X position registers. */
// First the X start register is set. This value informs the
// hardware how many pixels to count across into the image
// before starting display.
Setting the Displayed Sprite Position
S-MOS Systems, Inc. • Tel: [phone] • Fax: [phone] • http://www.smos.com
Xpos = CursorX;
Xstart = 0;
}
Xpos = 0;
Xstart = 0 - CursorX
}
Xpos = 0 - SpriteLeft
Xstart = 0
YES
// (SpriteLeft)
SpriteLeft = 0
X12-AN-002-01
Xpos = 0
Xstart = 0 - SpriteLeft
NO
411-1.0
SPC8106