jpayne@68: jpayne@68: jpayne@68: jpayne@68: jpayne@68: Image Surfaces: Cairo: A Vector Graphics Library jpayne@68: jpayne@68: jpayne@68: jpayne@68: jpayne@68: jpayne@68: jpayne@68: jpayne@68: jpayne@68: jpayne@68: jpayne@68: jpayne@68: jpayne@68: jpayne@68: jpayne@68: jpayne@68: jpayne@68:
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Image Surfaces

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Image Surfaces — Rendering to memory buffers

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Functions

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jpayne@68: int jpayne@68: jpayne@68: cairo_format_stride_for_width () jpayne@68:
jpayne@68: cairo_surface_t * jpayne@68: jpayne@68: cairo_image_surface_create () jpayne@68:
jpayne@68: cairo_surface_t * jpayne@68: jpayne@68: cairo_image_surface_create_for_data () jpayne@68:
unsigned char * jpayne@68: jpayne@68: cairo_image_surface_get_data () jpayne@68:
jpayne@68: cairo_format_t jpayne@68: jpayne@68: cairo_image_surface_get_format () jpayne@68:
jpayne@68: int jpayne@68: jpayne@68: cairo_image_surface_get_width () jpayne@68:
jpayne@68: int jpayne@68: jpayne@68: cairo_image_surface_get_height () jpayne@68:
jpayne@68: int jpayne@68: jpayne@68: cairo_image_surface_get_stride () jpayne@68:
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Types and Values

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#defineCAIRO_HAS_IMAGE_SURFACE
enumcairo_format_t
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Description

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Image surfaces provide the ability to render to memory buffers jpayne@68: either allocated by cairo or by the calling code. The supported jpayne@68: image formats are those defined in cairo_format_t.

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Functions

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cairo_format_stride_for_width ()

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int
jpayne@68: cairo_format_stride_for_width (cairo_format_t format,
jpayne@68:                                int width);
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This function provides a stride value that will respect all jpayne@68: alignment requirements of the accelerated image-rendering code jpayne@68: within cairo. Typical usage will be of the form:

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int stride;
jpayne@68: unsigned char *data;
jpayne@68: cairo_surface_t *surface;
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jpayne@68: stride = cairo_format_stride_for_width (format, width);
jpayne@68: data = malloc (stride * height);
jpayne@68: surface = cairo_image_surface_create_for_data (data, format,
jpayne@68: 					  width, height,
jpayne@68: 					  stride);
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Parameters

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format

A cairo_format_t value

 

width

The desired width of an image surface to be created.

 
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Returns

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the appropriate stride to use given the desired jpayne@68: format and width, or -1 if either the format is invalid or the width jpayne@68: too large.

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Since: 1.6

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cairo_image_surface_create ()

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cairo_surface_t *
jpayne@68: cairo_image_surface_create (cairo_format_t format,
jpayne@68:                             int width,
jpayne@68:                             int height);
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Creates an image surface of the specified format and jpayne@68: dimensions. Initially the surface contents are set to 0. jpayne@68: (Specifically, within each pixel, each color or alpha channel jpayne@68: belonging to format will be 0. The contents of bits within a pixel, jpayne@68: but not belonging to the given format are undefined).

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Parameters

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format

format of pixels in the surface to create

 

width

width of the surface, in pixels

 

height

height of the surface, in pixels

 
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Returns

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a pointer to the newly created surface. The caller jpayne@68: owns the surface and should call cairo_surface_destroy() when done jpayne@68: with it.

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This function always returns a valid pointer, but it will return a jpayne@68: pointer to a "nil" surface if an error such as out of memory jpayne@68: occurs. You can use cairo_surface_status() to check for this.

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Since: 1.0

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cairo_image_surface_create_for_data ()

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cairo_surface_t *
jpayne@68: cairo_image_surface_create_for_data (unsigned char *data,
jpayne@68:                                      cairo_format_t format,
jpayne@68:                                      int width,
jpayne@68:                                      int height,
jpayne@68:                                      int stride);
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Creates an image surface for the provided pixel data. The output jpayne@68: buffer must be kept around until the cairo_surface_t is destroyed jpayne@68: or cairo_surface_finish() is called on the surface. The initial jpayne@68: contents of data jpayne@68: will be used as the initial image contents; you jpayne@68: must explicitly clear the buffer, using, for example, jpayne@68: cairo_rectangle() and cairo_fill() if you want it cleared.

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Note that the stride may be larger than jpayne@68: width*bytes_per_pixel to provide proper alignment for each pixel jpayne@68: and row. This alignment is required to allow high-performance rendering jpayne@68: within cairo. The correct way to obtain a legal stride value is to jpayne@68: call cairo_format_stride_for_width() with the desired format and jpayne@68: maximum image width value, and then use the resulting stride value jpayne@68: to allocate the data and to create the image surface. See jpayne@68: cairo_format_stride_for_width() for example code.

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Parameters

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data

a pointer to a buffer supplied by the application in which jpayne@68: to write contents. This pointer must be suitably aligned for any jpayne@68: kind of variable, (for example, a pointer returned by malloc).

 

format

the format of pixels in the buffer

 

width

the width of the image to be stored in the buffer

 

height

the height of the image to be stored in the buffer

 

stride

the number of bytes between the start of rows in the jpayne@68: buffer as allocated. This value should always be computed by jpayne@68: cairo_format_stride_for_width() before allocating the data jpayne@68: buffer.

 
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Returns

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a pointer to the newly created surface. The caller jpayne@68: owns the surface and should call cairo_surface_destroy() when done jpayne@68: with it.

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This function always returns a valid pointer, but it will return a jpayne@68: pointer to a "nil" surface in the case of an error such as out of jpayne@68: memory or an invalid stride value. In case of invalid stride value jpayne@68: the error status of the returned surface will be jpayne@68: CAIRO_STATUS_INVALID_STRIDE. You can use jpayne@68: cairo_surface_status() to check for this.

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See cairo_surface_set_user_data() for a means of attaching a jpayne@68: destroy-notification fallback to the surface if necessary.

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Since: 1.0

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cairo_image_surface_get_data ()

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unsigned char *
jpayne@68: cairo_image_surface_get_data (cairo_surface_t *surface);
jpayne@68:

Get a pointer to the data of the image surface, for direct jpayne@68: inspection or modification.

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A call to cairo_surface_flush() is required before accessing the jpayne@68: pixel data to ensure that all pending drawing operations are jpayne@68: finished. A call to cairo_surface_mark_dirty() is required after jpayne@68: the data is modified.

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Parameters

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surface

a cairo_image_surface_t

 
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Returns

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a pointer to the image data of this surface or NULL jpayne@68: if surface jpayne@68: is not an image surface, or if cairo_surface_finish() jpayne@68: has been called.

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Since: 1.2

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cairo_image_surface_get_format ()

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cairo_format_t
jpayne@68: cairo_image_surface_get_format (cairo_surface_t *surface);
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Get the format of the surface.

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Parameters

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surface

a cairo_image_surface_t

 
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Returns

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the format of the surface

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Since: 1.2

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cairo_image_surface_get_width ()

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int
jpayne@68: cairo_image_surface_get_width (cairo_surface_t *surface);
jpayne@68:

Get the width of the image surface in pixels.

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Parameters

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surface

a cairo_image_surface_t

 
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Returns

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the width of the surface in pixels.

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Since: 1.0

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cairo_image_surface_get_height ()

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int
jpayne@68: cairo_image_surface_get_height (cairo_surface_t *surface);
jpayne@68:

Get the height of the image surface in pixels.

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Parameters

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surface

a cairo_image_surface_t

 
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Returns

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the height of the surface in pixels.

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Since: 1.0

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cairo_image_surface_get_stride ()

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int
jpayne@68: cairo_image_surface_get_stride (cairo_surface_t *surface);
jpayne@68:

Get the stride of the image surface in bytes

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Parameters

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surface

a cairo_image_surface_t

 
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Returns

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the stride of the image surface in bytes (or 0 if jpayne@68: surface jpayne@68: is not an image surface). The stride is the distance in jpayne@68: bytes from the beginning of one row of the image data to the jpayne@68: beginning of the next row.

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Since: 1.2

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Types and Values

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CAIRO_HAS_IMAGE_SURFACE

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#define CAIRO_HAS_IMAGE_SURFACE 1
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Defined if the image surface backend is available. jpayne@68: The image surface backend is always built in. jpayne@68: This macro was added for completeness in cairo 1.8.

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Since: 1.8

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enum cairo_format_t

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cairo_format_t is used to identify the memory format of jpayne@68: image data.

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New entries may be added in future versions.

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Members

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CAIRO_FORMAT_INVALID

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no such format exists or is supported.

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CAIRO_FORMAT_ARGB32

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each pixel is a 32-bit quantity, with jpayne@68: alpha in the upper 8 bits, then red, then green, then blue. jpayne@68: The 32-bit quantities are stored native-endian. Pre-multiplied jpayne@68: alpha is used. (That is, 50% transparent red is 0x80800000, jpayne@68: not 0x80ff0000.) (Since 1.0)

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CAIRO_FORMAT_RGB24

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each pixel is a 32-bit quantity, with jpayne@68: the upper 8 bits unused. Red, Green, and Blue are stored jpayne@68: in the remaining 24 bits in that order. (Since 1.0)

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CAIRO_FORMAT_A8

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each pixel is a 8-bit quantity holding jpayne@68: an alpha value. (Since 1.0)

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CAIRO_FORMAT_A1

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each pixel is a 1-bit quantity holding jpayne@68: an alpha value. Pixels are packed together into 32-bit jpayne@68: quantities. The ordering of the bits matches the jpayne@68: endianness of the platform. On a big-endian machine, the jpayne@68: first pixel is in the uppermost bit, on a little-endian jpayne@68: machine the first pixel is in the least-significant bit. (Since 1.0)

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CAIRO_FORMAT_RGB16_565

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each pixel is a 16-bit quantity jpayne@68: with red in the upper 5 bits, then green in the middle jpayne@68: 6 bits, and blue in the lower 5 bits. (Since 1.2)

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CAIRO_FORMAT_RGB30

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like RGB24 but with 10bpc. (Since 1.12)

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Since: 1.0

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See Also

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cairo_surface_t

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