Php 什么是图像资源标识符？

我正在阅读函数

imagecreatetruecolor

的php，该函数成功返回图像资源标识符。“图像资源标识符”是什么意思？我在PHP文档中搜索了这个术语，但在文档的前两页中没有找到它。

它基本上只是一种特殊类型的对象，用于

gdlib

-其他函数将需要此资源作为参数，例如

它存储有关正在创建的图像的信息，以便稍后使用其他函数进行进一步修改

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php.net中关于资源的一点信息

图像资源标识符是一种结构（用C术语）定义，用于保存有关图像的信息。以下是它在PHP源代码中的定义：

typedef struct gdImageStruct {
    /* Palette-based image pixels */
    unsigned char ** pixels;
    int sx;
    int sy;
    /* These are valid in palette images only. See also
        'alpha', which appears later in the structure to
        preserve binary backwards compatibility */
    int colorsTotal;
    int red[gdMaxColors];
    int green[gdMaxColors];
    int blue[gdMaxColors];
    int open[gdMaxColors];
    /* For backwards compatibility, this is set to the
        first palette entry with 100% transparency,
        and is also set and reset by the
        gdImageColorTransparent function. Newer
        applications can allocate palette entries
        with any desired level of transparency; however,
        bear in mind that many viewers, notably
        many web browsers, fail to implement
        full alpha channel for PNG and provide
        support for full opacity or transparency only. */
    int transparent;
    int *polyInts;
    int polyAllocated;
    struct gdImageStruct *brush;
    struct gdImageStruct *tile;
    int brushColorMap[gdMaxColors];
    int tileColorMap[gdMaxColors];
    int styleLength;
    int stylePos;
    int *style;
    int interlace;
    /* New in 2.0: thickness of line. Initialized to 1. */
    int thick;
    /* New in 2.0: alpha channel for palettes. Note that only
        Macintosh Internet Explorer and (possibly) Netscape 6
        really support multiple levels of transparency in
        palettes, to my knowledge, as of 2/15/01. Most
        common browsers will display 100% opaque and
        100% transparent correctly, and do something
        unpredictable and/or undesirable for levels
        in between. TBB */
    int alpha[gdMaxColors];
    /* Truecolor flag and pixels. New 2.0 fields appear here at the
        end to minimize breakage of existing object code. */
    int trueColor;
    int ** tpixels;
    /* Should alpha channel be copied, or applied, each time a
        pixel is drawn? This applies to truecolor images only.
        No attempt is made to alpha-blend in palette images,
        even if semitransparent palette entries exist.
        To do that, build your image as a truecolor image,
        then quantize down to 8 bits. */
    int alphaBlendingFlag;
    /* Should antialias functions be used */
    int antialias;
    /* Should the alpha channel of the image be saved? This affects
        PNG at the moment; other future formats may also
        have that capability. JPEG doesn't. */
    int saveAlphaFlag;


    /* 2.0.12: anti-aliased globals */
    int AA;
    int AA_color;
    int AA_dont_blend;
    unsigned char **AA_opacity;
    int AA_polygon;
    /* Stored and pre-computed variables for determining the perpendicular
     * distance from a point to the anti-aliased line being drawn:
     */
    int AAL_x1;
    int AAL_y1;
    int AAL_x2;
    int AAL_y2;
    int AAL_Bx_Ax;
    int AAL_By_Ay;
    int AAL_LAB_2;
    float AAL_LAB;

    /* 2.0.12: simple clipping rectangle. These values must be checked for safety when set; please use gdImageSetClip */
    int cx1;
    int cy1;
    int cx2;
    int cy2;
    gdInterpolationMethod interpolation_id;
    interpolation_method interpolation;
} gdImage;

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请参阅手册中的示例-这是您创建的图像资源。随后调用的每个GD函数都需要该图像标识符来知道它应该处理哪个图像。就php而言，可以使用该变量来标识特定图像。大致相当于windows land中的HBITMAP。它可能只是一个表示图像的对象，用于其他图像查询和操作方法。