Architecture

STM7710

14/23

2.9.2

Cursor layer

The cursor is defined as a 128 x 128 pixel area held in local memory, in ACLUT8 format.

Each cursor entry is a 16-bit ARGB4444 color + alpha value. The alpha factor of four bits

handles an antialiased cursor pattern on top of the composed output picture. The cursor-

plane features are:

●

ACLUT8 format, with ARGB4444 CLUT entries. 256 colors can be simultaneously

displayed for the cursor pattern, among 4096 colors associated with a 16-level

translucency channel.

●

Size is programmable up to 128 x 128.

●

Hardware rectangular clipping window, out of which the cursor is never displayed (per-

pixel clipping, so only part of the cursor can be out of this window, therefore

transparent).

●

Current bitmap is specified using a pointer register to an external memory location,

making cursor animation easy.

●

Programmable pitch, so all cursor patterns can be stored in a single global bitmap.

2.10

Display compositor

The graphic compositor consists of a five-layer digital mixer (Mix1) intended for the main TV

display (Figure 6) and a two-layer digital mixer (Mix2) intended as an auxiliary display for

applications including connection to a VCR (Figure 7).

Each mixer alpha blends graphics and video layers on a pixel-by-pixel basis based on alpha

component values provided by each layer.

The Mix1 display planes are:

●

A background color (RGB888 format, programmable through the registers),

●

The two graphics layers GDP1 and GDP2,

●

The main video display,

●

The cursor plane.