The CairoFormat class

(No version information available, might only be in SVN)

简介

CairoFormat enums are used to identify the memory format of the image data.

CairoFormat {

/* 常量 */

const integer ARGB32 = 0 ;

const integer RGB24 = 1 ;

const integer A8 = 2 ;

const integer A1 = 3 ;

/* 方法 */

public static int strideForWidth ( int $format , int $width )

}

CairoFormat::ARGB32: Each pixel is a 32-bit quantity, with alpha in the upper 8 bits, then red, then green, then blue. The 32-bit quantities are stored native-endian. Pre-multiplied alpha is used. (That is, 50% transparent red is 0x80800000, not 0x80ff0000.)
CairoFormat::RGB24: Each pixel is a 32-bit quantity, with the upper 8 bits unused. Red, Green, and Blue are stored in the remaining 24 bits in that order.
CairoFormat::A8: Each pixel is a 8-bit quantity holding an alpha value.
CairoFormat::A1: Each pixel is a 1-bit quantity holding an alpha value. Pixels are packed together into 32-bit quantities. The ordering of the bits matches the endianess of the platform. On a big-endian machine, the first pixel is in the uppermost bit, on a little-endian machine the first pixel is in the least-significant bit.