AMD SC3200 manual Color/Chroma Key and Mixer/Blender, Graphics Window, Video Window, Cursor Window

32581C Video Processor Module

7.2.3.4Color/Chroma Key and Mixer/Blender

The Mixer/Blender takes each pixel of the graphics and video data streams and mixes or blends them together. Mixing is simply choosing the graphics pixel or the video pixel. Blending takes a percentage of a graphics pixel (Alpha_value * Graphics_pixel_value) and percentage of the video pixel (1 - Alpha_Value * Video_pixel_value) and adds them together. The percentages of each add up to

100%. The actual formula is:

•Blended Pixel = (Alpha_value * Graphics_pixel_value) / 256 + ((256 – Alpha_value) * Video_pixel_value) / 256

Where: Alpha_value = 0 to 255

Mixing and blending are supported simultaneously for every rendered frame, however, each pixel can only be mixed or blended. The mix or blend question is decided by the pixel position, whether video is overlaid on the graphics or visa versa (GFX_INS_VIDEO, F4BAR0+Memory Offset 4Ch[8]), and several programmed “windows”. Figure 7-11illustrates and example frame.

Graphics Window

The graphics window is defined in the GX1 module’s dis- play controller and is always the full screen resolution.

Video Window

The video window tells the Mixer/Blender where the video window is and its size. If Direct Video mode is enabled (see Section 7.2.1.1 "Direct Video Mode" on page 313), the video window must be defined as the resolution of the video port data resolution (720x480 for NTSC, 720x576 for

PAL). Vertical scaling is not allowed. Horizontal scaling is allowed. If the video source is from the GX1 module’s video frame buffer (which includes Capture Video mode, see Section 7.2.1.2 "Capture Video Mode" on page 314) then the video data can be scaled both horizontally and verti- cally. The video data size, scaled or unscaled, must equal the video window size. The Video X Position (horizontal) and Video Y Position (vertical) registers (F4BAR0+Memory Offset 08h and 0Ch) define the video window.

Cursor Window

The cursor window can be managed two ways: with the GX1 module’s hardware cursor or a software cursor. When using the hardware cursor, the displayed colors of the hard- ware cursor must be the cursor color keys (see Section

5.5.3“Hardware Cursor” in the AMD Geode™ GX1 Pro- cessor Data Book). When the software cursor is used, the cursor size and position are not defined using registers. The cursor size, position, and image are determined through the use of the cursor color key colors in the graph- ics frame buffer. When the cursor is described in this man- ner, the cursor can be of any size and shape.

Alpha Windows

Up to three alpha windows can be defined. They are used only for blending. They can be of any size up to the graph- ics window size and they may overlap. To support overlap- ping of the alpha windows they can be prioritized as to which one is on top (F4BAR0+Memory Offset 4Ch[20:16]). The alpha windows are programmed at F4BAR0+Memory Offset 60h-88h.

	Graphics Window (GFX_INS_VIDEO = 0)
	Video Window
	Video X
	Position Register
Cursor		Alpha
Window
	Alpha Window #1 Window
Video Y
Position			Alpha
Register			Window 3
		#2
			Y Position
		Alpha Window 3	Register
	ALPHA1_WIN_PRIORITY = 10	X Position
	ALPHA2_WIN_PRIORITY = 01	Register
	ALPHA3_WIN_PRIORITY = 00
	Alpha Window #3

Figure 7-11. Graphics/Video Frame with Alpha Windows

322 AMD Geode™ SC3200 Processor Data Book