Using Color QuickDraw

If your application uses color in straightforward ways, it will probably

execute without change in a direct pixel environment.

For most other applications, the main concern is in the creation and use of

special-purpose pixel map and graphics device records. By using the off screen

graphics world routines described in the separate section en titled,

Graphics Devices Manager , you will find such tasks far easier than

before.

If you must work with color grafPort, pixel map, and graphics device records

in ways beyond the scope of the offscreen graphics world routines, the

following guidelines may aid you in adapting to the Color QuickDraw

direct pixel environment:

• Don't draw directly to the screen. Create your own offscreen graphics

• Don't directly change the fgColor or bkColor field of a grafPort and

expect them to be used as the pixel values. Color QuickDraw

recalculates these values for each device. If you really want to draw in

an index instead of a color, use a palette with explicit colors, as

described in the Palette Manager . For device-independent colors,

use the RGBForeColor and RGBBackColor procedures.

• Fill out all the fields in a new pixel map record. The NewPixMap

function returns a pixel map record that is cloned from the pixel map

record pointed to by theGDevice. If you don't want a copy of the main

screen's pixel map record-for example, you want one that is a

different depth-then you must fill out more fields than just pixelSize:

you must fill out the pixelType, cmpCount, and cmpSize fields. Set

pmVersion to 0 when initializing your own pixel map record. For

future compatibility you should also set packType, packSize,

planeBytes, and pmReserved to 0.

• Don't clone a graphics device record's pixel map record. Instead, use

the NewPixMap function or the CopyPixMap procedure. If you must

create or manually clone a pixel map record, make sure to set the

pmVersion field and other unused fields to 0 for future compatibility.

• Fill out all the fields of a new graphics device record. When creating

an offscreen graphics device record by calling NewGDevice with the

mode parameter set to -1, you must fill out the fields of the graphics

device record (for instance, gdType) yourself. If you want a copy of an

existing graphics device record, then copy the gdType field from it. If

you explicitly want an indexed device, then set gdType to 0.

• Don't assume a pixel map record has a color table. A direct pixel map

record need not have a color table. For compatibility, a direct pixel

map record should have a dummy pmTable handle that points to a color

table header with a seed value equal to cmpSize * cmpCount, and the

color table's ctSize field should be set to 0.

Again, all these problems are simplified if you use the offscreen graphics

world routines.