# 预定义常量

下列常量由此扩展定义，且仅在此扩展编译入 PHP 或在运行时动态载入时可用。

`GD_VERSION` (string)
  PHP 编译所依据的 GD 版本。
`GD_MAJOR_VERSION` (int)
  PHP 编译所依据的 GD 大版本。
`GD_MINOR_VERSION` (int)
  PHP 编译所依据的 GD 小版本。
`GD_RELEASE_VERSION` (int)
  PHP 编译所依据的 GD 发布版本。
`GD_EXTRA_VERSION` (string)
  PHP 编译所依据的 GD 扩展版本（beta/rc..）。
`GD_BUNDLED` (int)
  当使用绑定版本的 GD 时，此值为 1，反之为 0。
`IMG_AVIF` (int)
  Used as a return value by imagetypes() （自 PHP 8.1.0 起可用）
`IMG_BMP` (int)
  Used as a return value by imagetypes()
`IMG_GIF` (int)
  Used as a return value by imagetypes()
`IMG_JPG` (int)
  Used as a return value by imagetypes()
`IMG_JPEG` (int)
  Used as a return value by imagetypes()

  > 注意:

  > 本常量值同 `IMG_JPG`

`IMG_PNG` (int)
  Used as a return value by imagetypes()
`IMG_TGA` (int)
  Used as a return value by imagetypes() （自 PHP 7.4.0 起可用）
`IMG_WBMP` (int)
  Used as a return value by imagetypes()
`IMG_XPM` (int)
  Used as a return value by imagetypes()
`IMG_WEBP` (int)
  Used as a return value by imagetypes() （自 PHP 7.0.10 起可用）
`IMG_WEBP_LOSSLESS` (int)
  （自 PHP 8.1.0 起可用）
`IMG_COLOR_TILED` (int)
  Special color option which can be used instead of a color allocated with imagecolorallocate() or imagecolorallocatealpha().
`IMG_COLOR_STYLED` (int)
  Special color option which can be used instead of a color allocated with imagecolorallocate() or imagecolorallocatealpha().
`IMG_COLOR_BRUSHED` (int)
  Special color option which can be used instead of a color allocated with imagecolorallocate() or imagecolorallocatealpha().
`IMG_COLOR_STYLEDBRUSHED` (int)
  Special color option which can be used instead of a color allocated with imagecolorallocate() or imagecolorallocatealpha().
`IMG_COLOR_TRANSPARENT` (int)
  Special color option which can be used instead of a color allocated with imagecolorallocate() or imagecolorallocatealpha().
`IMG_AFFINE_TRANSLATE` (int)
  An affine transformation type constant used by the imageaffinematrixget() function.
`IMG_AFFINE_SCALE` (int)
  An affine transformation type constant used by the imageaffinematrixget() function.
`IMG_AFFINE_ROTATE` (int)
  An affine transformation type constant used by the imageaffinematrixget() function.
`IMG_AFFINE_SHEAR_HORIZONTAL` (int)
  An affine transformation type constant used by the imageaffinematrixget() function.
`IMG_AFFINE_SHEAR_VERTICAL` (int)
  An affine transformation type constant used by the imageaffinematrixget() function.
`IMG_ARC_ROUNDED` (int)
  A style constant used by the imagefilledarc() function.

  > 注意:

  > 此常量值同 `IMG_ARC_PIE`

`IMG_ARC_PIE` (int)
  A style constant used by the imagefilledarc() function.
`IMG_ARC_CHORD` (int)
  A style constant used by the imagefilledarc() function.
`IMG_ARC_NOFILL` (int)
  A style constant used by the imagefilledarc() function.
`IMG_ARC_EDGED` (int)
  A style constant used by the imagefilledarc() function.
`IMG_GD2_RAW` (int)
  A type constant used by the imagegd2() function.
`IMG_GD2_COMPRESSED` (int)
  A type constant used by the imagegd2() function.
`IMG_EFFECT_REPLACE` (int)
  Alpha blending effect used by the imagelayereffect() function.
`IMG_EFFECT_ALPHABLEND` (int)
  Alpha blending effect used by the imagelayereffect() function.
`IMG_EFFECT_NORMAL` (int)
  Alpha blending effect used by the imagelayereffect() function.
`IMG_EFFECT_OVERLAY` (int)
  Alpha blending effect used by the imagelayereffect() function.
`IMG_EFFECT_MULTIPLY` (int)
  Alpha blending effect used by the imagelayereffect() function.
`IMG_FILTER_NEGATE` (int)
  Special GD filter used by the imagefilter() function.
`IMG_FILTER_GRAYSCALE` (int)
  Special GD filter used by the imagefilter() function.
`IMG_FILTER_BRIGHTNESS` (int)
  Special GD filter used by the imagefilter() function.
`IMG_FILTER_CONTRAST` (int)
  Special GD filter used by the imagefilter() function.
`IMG_FILTER_COLORIZE` (int)
  Special GD filter used by the imagefilter() function.
`IMG_FILTER_EDGEDETECT` (int)
  Special GD filter used by the imagefilter() function.
`IMG_FILTER_GAUSSIAN_BLUR` (int)
  Special GD filter used by the imagefilter() function.
`IMG_FILTER_SELECTIVE_BLUR` (int)
  Special GD filter used by the imagefilter() function.
`IMG_FILTER_EMBOSS` (int)
  Special GD filter used by the imagefilter() function.
`IMG_FILTER_MEAN_REMOVAL` (int)
  Special GD filter used by the imagefilter() function.
`IMG_FILTER_SMOOTH` (int)
  Special GD filter used by the imagefilter() function.
`IMG_FILTER_PIXELATE` (int)
  Special GD filter used by the imagefilter() function.
`IMG_FILTER_SCATTER` (int)
  Special GD filter used by the imagefilter() function. （自 PHP 7.4.0 版本可用）
`IMAGETYPE_GIF` (int)
  Image type constant used by the image_type_to_mime_type() and image_type_to_extension() functions.
`IMAGETYPE_JPEG` (int)
  Image type constant used by the image_type_to_mime_type() and image_type_to_extension() functions.
`IMAGETYPE_JPEG2000` (int)
  Image type constant used by the image_type_to_mime_type() and image_type_to_extension() functions.
`IMAGETYPE_PNG` (int)
  Image type constant used by the image_type_to_mime_type() and image_type_to_extension() functions.
`IMAGETYPE_SWF` (int)
  Image type constant used by the image_type_to_mime_type() and image_type_to_extension() functions.
`IMAGETYPE_PSD` (int)
  Image type constant used by the image_type_to_mime_type() and image_type_to_extension() functions.
`IMAGETYPE_BMP` (int)
  Image type constant used by the image_type_to_mime_type() and image_type_to_extension() functions.
`IMAGETYPE_WBMP` (int)
  Image type constant used by the image_type_to_mime_type() and image_type_to_extension() functions.
`IMAGETYPE_XBM` (int)
  Image type constant used by the image_type_to_mime_type() and image_type_to_extension() functions.
`IMAGETYPE_TIFF_II` (int)
  Image type constant used by the image_type_to_mime_type() and image_type_to_extension() functions.
`IMAGETYPE_TIFF_MM` (int)
  Image type constant used by the image_type_to_mime_type() and image_type_to_extension() functions.
`IMAGETYPE_IFF` (int)
  Image type constant used by the image_type_to_mime_type() and image_type_to_extension() functions.
`IMAGETYPE_JB2` (int)
  Image type constant used by the image_type_to_mime_type() and image_type_to_extension() functions.
`IMAGETYPE_JPC` (int)
  Image type constant used by the image_type_to_mime_type() and image_type_to_extension() functions.
`IMAGETYPE_JP2` (int)
  Image type constant used by the image_type_to_mime_type() and image_type_to_extension() functions.
`IMAGETYPE_JPX` (int)
  Image type constant used by the image_type_to_mime_type() and image_type_to_extension() functions.
`IMAGETYPE_SWC` (int)
  Image type constant used by the image_type_to_mime_type() and image_type_to_extension() functions.
`IMAGETYPE_ICO` (int)
  Image type constant used by the image_type_to_mime_type() and image_type_to_extension() functions.
`IMAGETYPE_WEBP` (int)
  Image type constant used by the image_type_to_mime_type() and image_type_to_extension() functions. (从 PHP 7.1.0 开始支持)
`IMAGETYPE_AVIF` (int)
  Image type constant used by the image_type_to_mime_type() and image_type_to_extension() functions. （自 PHP 8.1.0 起可用）
`IMAGETYPE_UNKNOWN` (int)
  Image type constant used by the image_type_to_mime_type() and image_type_to_extension() functions.
`IMAGETYPE_COUNT` (int)
  可用于 image_type_to_mime_type() 和 image_type_to_extension() 函数的图像类型常量编号（包括 unknown 类型）。
`PNG_NO_FILTER` (int)
  A special PNG filter, used by the imagepng() function.
`PNG_FILTER_NONE` (int)
  A special PNG filter, used by the imagepng() function.
`PNG_FILTER_SUB` (int)
  A special PNG filter, used by the imagepng() function.
`PNG_FILTER_UP` (int)
  A special PNG filter, used by the imagepng() function.
`PNG_FILTER_AVG` (int)
  A special PNG filter, used by the imagepng() function.
`PNG_FILTER_PAETH` (int)
  A special PNG filter, used by the imagepng() function.
`PNG_ALL_FILTERS` (int)
  A special PNG filter, used by the imagepng() function.
`IMG_FLIP_VERTICAL` (int)
  Used together with imageflip(), available as of PHP 5.5.0.
`IMG_FLIP_HORIZONTAL` (int)
  Used together with imageflip(), available as of PHP 5.5.0.
`IMG_FLIP_BOTH` (int)
  Used together with imageflip(), available as of PHP 5.5.0.
`IMG_BELL` (int)
  Used together with imagesetinterpolation(), available as of PHP 5.5.0.
`IMG_BESSEL` (int)
  Used together with imagesetinterpolation(), available as of PHP 5.5.0.
`IMG_BILINEAR_FIXED` (int)
  Used together with imagesetinterpolation(), available as of PHP 5.5.0.
`IMG_BICUBIC` (int)
  Used together with imagesetinterpolation(), available as of PHP 5.5.0.
`IMG_BICUBIC` (int)
  Used together with imagesetinterpolation(), available as of PHP 5.5.0.
`IMG_BLACKMAN` (int)
  Used together with imagesetinterpolation(), available as of PHP 5.5.0.
`IMG_BOX` (int)
  Used together with imagesetinterpolation(), available as of PHP 5.5.0.
`IMG_BSPLINE` (int)
  Used together with imagesetinterpolation(), available as of PHP 5.5.0.
`IMG_CATMULLROM` (int)
  Used together with imagesetinterpolation(), available as of PHP 5.5.0.
`IMG_GAUSSIAN` (int)
  Used together with imagesetinterpolation(), available as of PHP 5.5.0.
`IMG_GENERALIZED_CUBIC` (int)
  Used together with imagesetinterpolation(), available as of PHP 5.5.0.
`IMG_HERMITE` (int)
  Used together with imagesetinterpolation(), available as of PHP 5.5.0.
`IMG_HAMMING` (int)
  Used together with imagesetinterpolation(), available as of PHP 5.5.0.
`IMG_HANNING` (int)
  Used together with imagesetinterpolation(), available as of PHP 5.5.0.
`IMG_MITCHELL` (int)
  Used together with imagesetinterpolation(), available as of PHP 5.5.0.
`IMG_POWER` (int)
  Used together with imagesetinterpolation(), available as of PHP 5.5.0.
`IMG_QUADRATIC` (int)
  Used together with imagesetinterpolation(), available as of PHP 5.5.0.
`IMG_SINC` (int)
  Used together with imagesetinterpolation(), available as of PHP 5.5.0.
`IMG_NEAREST_NEIGHBOUR` (int)
  Used together with imagesetinterpolation(), available as of PHP 5.5.0.
`IMG_WEIGHTED4` (int)
  Used together with imagesetinterpolation(), available as of PHP 5.5.0.
`IMG_TRIANGLE` (int)
  Used together with imagesetinterpolation(), available as of PHP 5.5.0.
`IMG_CROP_BLACK` (int)
  裁剪出黑色背景。
`IMG_CROP_DEFAULT` (int)
  等同于 `IMG_CROP_TRANSPARENT`。在 PHP 7.4.0 之前，如果图像没有透明色，则捆绑的 libgd 将恢复为 `IMG_CROP_SIDES`。
`IMG_CROP_SIDES` (int)
  使用图像的 4 个角尝试检测要裁剪的背景。
`IMG_CROP_THRESHOLD` (int)
  使用指定 `threshold` 和 `color` 裁切图片。
`IMG_CROP_TRANSPARENT` (int)
  裁剪出透明背景。
`IMG_CROP_WHITE` (int)
  裁剪出白色背景。

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