How Direct Pixels Work

When pixels are directly specified, the Color Manager's inverse table

look-up isn't needed. The color value is derived from the most significant 5 or

8 bits of each component. The first few steps are the same as the steps for

indexed devices.

The direct pixel path

As illustrated in this figure, the user tells the application to choose a color

for some object (1). The application calls the Color Picker (2), which offers

its color wheel dialog box to the user (3), who selects a color. The

Color Picker returns that color to the application as a full 48-bit RGB value

(4). The application tells Color QuickDraw to draw the object in that color

(5). Color QuickDraw knows from the graphics device record (6) that the

screen is a direct device in which pixels are 32 bits deep, which means that 8

bits are used for each of the red, green, and blue components (8 are unused).

Color QuickDraw passes the high 8 bits from each 16-bit component of its

48-bit RGB value to the card (7), which stores that 24-bit value in video

RAM for each location of the object. The card continuously displays video RAM

by sending the three 8-bit red, green, and blue values to digital-to-analog

converters (8) that produce a signal for the screen (9).

Referenced by (1):