## VipsRegion

VipsRegion — small, rectangular parts of images

## Stability Level

Stable, unless otherwise indicated

## Functions

VipsRegion * | vips_region_new ()
int | vips_region_buffer ()
int | vips_region_image ()
int | vips_region_region ()
int | vips_region_equalsregion ()
int | vips_region_position ()
void | vips_region_paint ()
void | vips_region_paint_pel ()
void | vips_region_black ()
void | vips_region_copy ()
int | vips_region_shrink ()
int | vips_region_prepare ()
int | vips_region_prepare_to ()
int | vips_region_prepare_many ()
void | vips_region_invalidate ()
void | vips_region_dump_all ()
void | vips__region_count_pixels ()
#define | VIPS_COUNT_PIXELS()
#define | VIPS_REGION_LSKIP()
#define | VIPS_REGION_N_ELEMENTS()
#define | VIPS_REGION_SIZEOF_LINE()
#define | VIPS_REGION_ADDR()
#define | VIPS_REGION_ADDR_TOPLEFT()

## Object Hierarchy

        GObject
        ╰── VipsObject
            ╰── VipsRegion

## Includes

    #include <vips/vips.h>

## Description

A VipsRegion is a small part of an image and some pixels. You use regions to read pixels out of images without having to have the whole image in memory at once.

A region can be a memory buffer, part of a memory-mapped file, part of some other image, or part of some other region.

Regions must be created, used and freed all within the same thread, since they can reference private per-thread caches. VIPS sanity-checks region ownership in various places, so you are likely to see `g_assert()` errors if you don't follow this rule.

There is API to transfer ownership of regions between threads, but hopefully this is only needed within VIPS, so we don't expose it. Hopefully.

## Functions

### vips_region_new ()

    VipsRegion *
    vips_region_new (VipsImage *image);

Create a region. VipsRegion s start out empty, you need to call `vips_region_prepare()` to fill them with pixels.

See also: `vips_region_prepare()`.

#### Parameters

image | image to create this region on |

### vips_region_buffer ()

    int
    vips_region_buffer (VipsRegion *reg,
                        VipsRect *r);

The region is transformed so that at least `r` pixels are available as a memory buffer.

#### Parameters

reg | region to operate upon |
r | VipsRect of pixels you need to be able to address |

#### Returns

0 on success, or -1 for error.

### vips_region_image ()

    int
    vips_region_image (VipsRegion *reg,
                       VipsRect *r);

The region is transformed so that at least `r` pixels are available directly from the image. The image needs to be a memory buffer or represent a file on disc that has been mapped or can be mapped.

#### Parameters

reg | region to operate upon |
r | VipsRect of pixels you need to be able to address |

#### Returns

0 on success, or -1 for error.

### vips_region_region ()

    int
    vips_region_region (VipsRegion *reg,
                        VipsRegion *dest,
                        VipsRect *r,
                        int x,
                        int y);

Make `VIPS_REGION_ADDR()` on `reg` go to `dest` instead.

`r` is the part of `reg` which you want to be able to address (this effectively becomes the valid field), (`x` , `y` ) is the top LH corner of the corresponding area in `dest` .

Performs all clipping necessary to ensure that `reg->valid` is indeed valid.

If the region we attach to is modified, we can be left with dangling pointers! If the region we attach to is on another image, the two images must have the same sizeof( pel ).

#### Parameters

reg | region to operate upon |
dest | region to connect to |
r | VipsRect of pixels you need to be able to address |
x | postion of `r` in `dest` |
y | postion of `r` in `dest` |

#### Returns

0 on success, or -1 for error.

### vips_region_equalsregion ()

    int
    vips_region_equalsregion (VipsRegion *reg1,
                              VipsRegion *reg2);

Do two regions point to the same piece of image? ie.

    1
    2
    3

    VIPS_REGION_ADDR( reg1, x, y ) == VIPS_REGION_ADDR( reg2, x, y ) &&
    *VIPS_REGION_ADDR( reg1, x, y ) ==
    	*VIPS_REGION_ADDR( reg2, x, y ) for all x, y, reg1, reg2.

#### Parameters

reg1 | region to test |
reg2 | region to test |

#### Returns

non-zero on equality.

### vips_region_position ()

    int
    vips_region_position (VipsRegion *reg,
                          int x,
                          int y);

Set the position of a region. This only affects reg->valid, ie. the way pixels are addressed, not reg->data, the pixels which are addressed. Clip against the size of the image. Do not allow negative positions, or positions outside the image.

#### Parameters

reg | region to operate upon |
x | position to move to |
y | position to move to |

#### Returns

0 on success, or -1 for error.

### vips_region_paint ()

    void
    vips_region_paint (VipsRegion *reg,
                       VipsRect *r,
                       int value);

Paints `value` into `reg` covering rectangle `r` . For int images, `value` is passed to `memset()`, so it usually needs to be 0 or 255. For float images, value is cast to a float and copied in to each band element.

`r` is clipped against `reg->valid` .

See also: `vips_region_black()`.

#### Parameters

reg | region to operate upon |
r | area to paint |
value | value to paint |

### vips_region_paint_pel ()

    void
    vips_region_paint_pel (VipsRegion *reg,
                           VipsRect *r,
                           VipsPel *ink);

Paints `ink` into `reg` covering rectangle `r` . `r` is clipped against `reg->valid` .

`ink` should be a byte array of the same size as an image pixel containing the binary value to write into the pixels.

See also: `vips_region_paint()`.

#### Parameters

reg | region to operate upon |
r | area to paint |
ink | value to paint |

### vips_region_black ()

    void
    vips_region_black (VipsRegion *reg);

Paints 0 into the valid part of `reg` .

See also: `vips_region_paint()`.

#### Parameters

reg | region to operate upon |

### vips_region_copy ()

    void
    vips_region_copy (VipsRegion *reg,
                      VipsRegion *dest,
                      VipsRect *r,
                      int x,
                      int y);

Copy from one region to another. Copy area `r` from inside `reg` to `dest` , positioning the area of pixels at `x` , `y` . The two regions must have pixels which are the same size.

See also: `vips_region_paint()`.

#### Parameters

reg | source region |
dest | destination region |
r | VipsRect of pixels you need to copy |
x | postion of `r` in `dest` |
y | postion of `r` in `dest` |

### vips_region_shrink ()

    int
    vips_region_shrink (VipsRegion *from,
                        VipsRegion *to,
                        VipsRect *target);

Write the pixels `target` in `to` from the x2 larger area in `from` . Non-complex uncoded images and LABQ only.

See also: `vips_region_copy()`.

#### Parameters

from | source region |
to | destination region |
target | VipsRect of pixels you need to copy |

### vips_region_prepare ()

    int
    vips_region_prepare (VipsRegion *reg,
                         VipsRect *r);

vips_region_prepare() fills `reg` with pixels. After calling, you can address at least the area `r` with `VIPS_REGION_ADDR()` and get valid pixels.

vips_region_prepare() runs in-line, that is, computation is done by the calling thread, no new threads are involved, and computation blocks until the pixels are ready.

Use `vips_sink_screen()` to calculate an area of pixels in the background.

See also: `vips_sink_screen()`, `vips_region_prepare_to()`.

#### Parameters

reg | region to prepare |
r | VipsRect of pixels you need to be able to address |

#### Returns

0 on success, or -1 on error.

### vips_region_prepare_to ()

    int
    vips_region_prepare_to (VipsRegion *reg,
                            VipsRegion *dest,
                            VipsRect *r,
                            int x,
                            int y);

Like `vips_region_prepare()`: fill `reg` with data, ready to be read from by our caller. Unlike `vips_region_prepare()`, rather than allocating memory local to `reg` for the result, we guarantee that we will fill the pixels in `dest` at offset `x` , `y` . In other words, we generate an extra copy operation if necessary.

Also unlike `vips_region_prepare()`, `dest` is not set up for writing for you with `vips_region_buffer()`. You can point `dest` at anything, and pixels really will be written there. This makes `vips_region_prepare_to()` useful for making the ends of pipelines, since it (effectively) makes a break in the pipe.

See also: `vips_region_prepare()`, `vips_sink_disc()`.

#### Parameters

reg | region to prepare |
dest | region to write to |
r | VipsRect of pixels you need to be able to address |
x | postion of `r` in `dest` |
y | postion of `r` in `dest` |

#### Returns

0 on success, or -1 on error

### vips_region_prepare_many ()

    int
    vips_region_prepare_many (VipsRegion **reg,
                              VipsRect *r);

### vips_region_invalidate ()

    void
    vips_region_invalidate (VipsRegion *reg);

Mark a region as containing invalid pixels. Calling this function means that the next time `vips_region_prepare()` is called, the region will be recalculated.

This is faster than calling `vips_image_invalidate_all()`, but obviously only affects a single region.

See also: `vips_image_invalidate_all()`, `vips_region_prepare()`.

#### Parameters

reg | region to invalidate |

### vips_region_dump_all ()

    void
    vips_region_dump_all (void);

### vips__region_count_pixels ()

    void
    vips__region_count_pixels (VipsRegion *region,
                               const char *nickname);

### VIPS_COUNT_PIXELS()

    #define VIPS_COUNT_PIXELS( R, N ) vips__region_count_pixels( R, N )

### VIPS_REGION_LSKIP()

    #define             VIPS_REGION_LSKIP( R )

#### Parameters

R | a VipsRegion |

#### Returns

The number of bytes to add to move down a scanline.

### VIPS_REGION_N_ELEMENTS()

    #define             VIPS_REGION_N_ELEMENTS( R )

#### Parameters

R | a VipsRegion |

#### Returns

The number of band elements across a region.

### VIPS_REGION_SIZEOF_LINE()

    #define             VIPS_REGION_SIZEOF_LINE( R )

#### Parameters

R | a VipsRegion |

#### Returns

The number of bytes across a region.

### VIPS_REGION_ADDR()

    #define             VIPS_REGION_ADDR( R, X, Y )

This macro returns a pointer to a pixel in a region. The (`X` , `Y` ) coordinates need to be within the VipsRect (`R->valid` ).

If DEBUG is defined, you get a version that checks bounds for you.

See also: `vips_region_prepare()`.

#### Parameters

R | a VipsRegion |
X | x coordinate |
Y | y coordinate |

#### Returns

The address of pixel (`X` ,`Y` ) in `R` .

### VIPS_REGION_ADDR_TOPLEFT()

    #define VIPS_REGION_ADDR_TOPLEFT( R ) ((R)->data)

This macro returns a pointer to the top-left pixel in the VipsRegion, that is, the pixel at (`R->valid.left` , `R->valid.top` ).

See also: `vips_region_prepare()`.

#### Parameters

R | a VipsRegion |

#### Returns

The address of the top-left pixel in the region.

## Types and Values

## See Also

image, generate