PHP Manual: Set the clipping rectangle

bool imagesetclip(
    GdImage $image,
    int $x1,
    int $y1,
    int $x2,
    int $y2
)

imagesetclip sets the current clipping rectangle, i.e. the area beyond which no pixels will be drawn.

image: A GdImage object, returned by one of the image creation functions, such as imagecreatetruecolor.
x1: The x-coordinate of the upper left corner.
y1: The y-coordinate of the upper left corner.
x2: The x-coordinate of the lower right corner.
y2: The y-coordinate of the lower right corner.

Returns true on success or false on failure.

Version	Description
8.0.0	`image` expects a GdImage instance now; previously, a valid `gd` resource was expected.

imagesetclip