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Video Processor Module (Continued)

6.2.3.4

Color/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 6-11

illustrates 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 6.2.1.1 "Direct Video Mode" on page 319), 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

Section6.2.1.2 "Capture VideoMode"onpage320)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

Thecursorwindow canbemanaged 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

4.5.3 “Hardware Cursor” in the GX1 datasheet). 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 graphics frame buffer. When the cursor is

described in this manner, 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.

Figure 6-11. Graphics/Video Frame with Alpha Windows

Graphics Window (GFX_INS_VIDEO = 0)

Video Window

Alpha Window #3

Cursor

Window

ALPHA1_WIN_PRIORITY = 10

ALPHA2_WIN_PRIORITY = 01

ALPHA3_WIN_PRIORITY = 00

Video X

Video Y

Position

Alpha Window 3

XPosition

Alpha

Window 3

YPosition

Alpha Window #1

Position Register

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