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pmVersion

PixMap structure

#include <Quickdraw.h>

typedef struct PixMap { Size Offset Description

Ptr baseAddr; 4 0 Address of start of bitmap data

short rowBytes; 2 4 Bytes per row in the bitmap data

Rect bounds; 8 6 Coordinates imposed over the bitmap

data

short pmVersion; 2 14 Version of Color QuickDraw

short packType; 2 16 Format of packing algorithm

long packSize; 4 18 Image's size after compression

fixed hRes; 4 22 Horizontal resolution in pixels per

inch

fixed vRes; 4 26 Vertical resolution (hres=vres=72)

short pixelType; 2 30 Pixel image storage format

short pixelSize; 2 32 Bits per pixel (always a power of 2)

short cmpCount; 2 34 Color components per pixel

short cmpSize; 2 36 Logical bits per RGBColor component

long planeBytes; 4 38 Offset in bytes to next plane

CTabHandle pmTable; 4 42 Handle to color table

long pmReserved; 4 46 Reserved for future expansion

} PixMap; 50

typedef PixMap *PixMapPtr;

typedef PixMap **PixMapHandle;

Field descriptions

rowBytes The restriction that the value of rowBytes be less than $2000 has

been relaxed: rowBytes must be less than $4000. The value must be

even, and for best performance it should be a multiple of 4.

pmVersion The value of pmVersion is normally 0. If pmVersion is 4, Color

QuickDraw treats the pixel map's baseAddr field as being 32-bit

clean. (All other flags are private.) Most applications never need to set

pmVersion.

pixelType Direct pixel values are specified by a pixelType field value of

RGBDirect, or 16. In a pixel map of the graphics device record for a

direct device, the pixelType field is set to the constant RGBDirect when

the screen depth is set.

pixelSize Pixel sizes must be powers of 2. The original Color QuickDraw

supported pixel sizes of 1, 2, 4, and 8 bits; with direct pixels, pixel

sizes may also be 16 and 32 bits.

cmpCount With indexed pixels, each pixel is a single value re presenting an index

in a color table, and therefore the cmpCount field of a pixel map record

is 1- the index is the single component. With direct pixels, each pixel

contains three components, one integer each for the intensities of red,

green, and blue, so cmpCount is 3. Other values are un defined.

cmpSize For an indexed pixel value, which has only one component, the value of

cmpSize is the same as the value of pixelSize: 1, 2, 4, or 8. A 32-bit

pixel consists of three components (red, green, and blue values) of 8

bits each. Since cmpCount * cmpSize (3 * 8 = 24) is less than the

value of pixelSize, 8 bits in the pixel are not part of any component.

These bits are unused: Color QuickDraw sets them to 0 in any image

it creates. If presented with a 32-bit image-for example, in the

CopyBits procedure-it passes whatever bits are there. (Generally,

therefore, your application should clear image memory to 0 before

creating a 32-bit image.)

A 16-bit pixel consists of three components of 5 bits each. This leaves

an unused high-order bit, which Color QuickDraw sets to 0.

Color QuickDraw expects that the sizes of all components are the

same, and that cmpCount * cmpSize is less than or equal to pixelSize.

In each direct pixel, the pixel value is the concatenation of the red, green, and

blue components, where red is in the most significant bits and blue is in the

least significant bits. The entire direct pixel is right aligned; unused bits

occupy the highest-order bits.