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gd_filename.c

Summary
gd_filename.c
Functions
gdSupportsFileTypeTests if a given file type is supported by GD.
gdImageCreateFromFileRead an image file of any supported.
gdImageFileWrites an image to a file in the format indicated by the filename.

Functions

gdSupportsFileType

int gdSupportsFileType(const char *filename,
int writing)

Tests if a given file type is supported by GD.

Given the name of an image file (which does not have to exist), returns 1 (i.e.  TRUE) if gdImageCreateFromFile can read a file of that type.  This is useful if you do not know which image types were enabled at compile time.

If writing is true, the result will be true only if gdImageFile can write a file of this type.

Note that filename parsing is done exactly the same as is done by gdImageCreateFromFile and gdImageFile and is subject to the same limitations.

Assuming LibGD is compiled with support for these image types, the following extensions are supported:

  • .gif
  • .gd, .gd2
  • .wbmp
  • .bmp
  • .xbm
  • .tga
  • .png
  • .jpg, .jpeg
  • .heif, .heix
  • .avif
  • .tiff, .tif
  • .webp
  • .xpm

Names are parsed case-insenstively.

Parameters

filenameFilename with tested extension.
writingFlag: true tests if writing works

Returns

GD_TRUE (1) if the file type is supported, GD_FALSE (0) if not.

gdImageCreateFromFile

gdImagePtr gdImageCreateFromFile(const char *filename)

Read an image file of any supported.

Given the path to a file, gdImageCreateFromFile will open the file, read its contents with the appropriate gdImageCreateFrom* function and return it.

File type is determined by the filename extension, so having an incorrect extension will probably not work.  For example, renaming PNG image “foo.png” to “foo.gif” and then attempting to load it will fail even if GD supports both formats.  See <gdSupportsFiletype> for more details.

NULL is returned on error.

Parameters

filenamethe input file name

Returns

A pointer to the new image or NULL if an error occurred.

gdImageFile

int gdImageFile(gdImagePtr im,
const char *filename)

Writes an image to a file in the format indicated by the filename.

File type is determined by the extension of the file name.  See <gdSupportsFiletype> for an overview of the parsing.

For file types that require extra arguments, gdImageFile attempts to use sane defaults:

<gdImageGd2>chunk size = 0, compression is enabled.
<gdImageJpeg>quality = -1 (i.e. the reasonable default)
<gdImageWBMP>foreground is the darkest available color

Everything else is called with the two-argument function and so will use the default values.

gdImageFile has some rudimentary error detection and will return GD_FALSE (0) if a detectable error occurred.  However, the image loaders do not normally return their error status so a result of GD_TRUE (1) does **not** mean the file was saved successfully.

Parameters

imThe image to save.
filenameThe path to the file to which the image is saved.

Returns

GD_FALSE (0) if an error was detected, GD_TRUE (1) if not.

int gdSupportsFileType(const char *filename,
int writing)
Tests if a given file type is supported by GD.
gdImagePtr gdImageCreateFromFile(const char *filename)
Read an image file of any supported.
int gdImageFile(gdImagePtr im,
const char *filename)
Writes an image to a file in the format indicated by the filename.
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