Image Surfaces: Cairo: A Vector Graphics Library

+ + +

Image Surfaces

Image Surfaces — Rendering to memory buffers

Functions

++++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

+int +	+cairo_format_stride_for_width () +
+cairo_surface_t * +	+cairo_image_surface_create () +
+cairo_surface_t * +	+cairo_image_surface_create_for_data () +
unsigned char * +	+cairo_image_surface_get_data () +
+cairo_format_t +	+cairo_image_surface_get_format () +
+int +	+cairo_image_surface_get_width () +
+int +	+cairo_image_surface_get_height () +
+int +	+cairo_image_surface_get_stride () +

Types and Values

++++ + + + + + + + + + + +

#define	CAIRO_HAS_IMAGE_SURFACE
enum	cairo_format_t

Description

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

Functions

cairo_format_stride_for_width ()

int
+cairo_format_stride_for_width (cairo_format_t format,
+                               int width);

This function provides a stride value that will respect all +alignment requirements of the accelerated image-rendering code +within cairo. Typical usage will be of the form:

+ + + + + + + +

1
+2
+3
+4
+5
+6
+7
+8
+9

int stride;
+unsigned char *data;
+cairo_surface_t *surface;
+
+stride = cairo_format_stride_for_width (format, width);
+data = malloc (stride * height);
+surface = cairo_image_surface_create_for_data (data, format,
+					  width, height,
+					  stride);

+ +

Parameters

+++++ + + + + + + + + + + + + +

format	A cairo_format_t value
width	The desired width of an image surface to be created.

Returns

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

Since: 1.6

cairo_image_surface_create ()

cairo_surface_t *
+cairo_image_surface_create (cairo_format_t format,
+                            int width,
+                            int height);

Creates an image surface of the specified format and +dimensions. Initially the surface contents are set to 0. +(Specifically, within each pixel, each color or alpha channel +belonging to format will be 0. The contents of bits within a pixel, +but not belonging to the given format are undefined).

Parameters

+++++ + + + + + + + + + + + + + + + + + +

format	format of pixels in the surface to create
width	width of the surface, in pixels
height	height of the surface, in pixels

Returns

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

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

Since: 1.0

cairo_image_surface_create_for_data ()

cairo_surface_t *
+cairo_image_surface_create_for_data (unsigned char *data,
+                                     cairo_format_t format,
+                                     int width,
+                                     int height,
+                                     int stride);

Creates an image surface for the provided pixel data. The output +buffer must be kept around until the cairo_surface_t is destroyed +or cairo_surface_finish() is called on the surface. The initial +contents of data + will be used as the initial image contents; you +must explicitly clear the buffer, using, for example, +cairo_rectangle() and cairo_fill() if you want it cleared.

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

Parameters

+++++ + + + + + + + + + + + + + + + + + + + + + + + + + + + +

data	a pointer to a buffer supplied by the application in which +to write contents. This pointer must be suitably aligned for any +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 +buffer as allocated. This value should always be computed by +`cairo_format_stride_for_width()` before allocating the data +buffer.

Returns

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

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

See cairo_surface_set_user_data() for a means of attaching a +destroy-notification fallback to the surface if necessary.

Since: 1.0

cairo_image_surface_get_data ()

unsigned char *
+cairo_image_surface_get_data (cairo_surface_t *surface);

CAIRO_HAS_IMAGE_SURFACE

#define CAIRO_HAS_IMAGE_SURFACE 1
+

Defined if the image surface backend is available. +The image surface backend is always built in. +This macro was added for completeness in cairo 1.8.

Since: 1.8

enum cairo_format_t

cairo_format_t is used to identify the memory format of +image data.

New entries may be added in future versions.

Members

+++++ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

CAIRO_FORMAT_INVALID	+ no such format exists or is supported. +
CAIRO_FORMAT_ARGB32	+ each pixel is a 32-bit quantity, with + alpha in the upper 8 bits, then red, then green, then blue. + The 32-bit quantities are stored native-endian. Pre-multiplied + alpha is used. (That is, 50% transparent red is 0x80800000, + not 0x80ff0000.) (Since 1.0) +
CAIRO_FORMAT_RGB24	+ each pixel is a 32-bit quantity, with + the upper 8 bits unused. Red, Green, and Blue are stored + in the remaining 24 bits in that order. (Since 1.0) +
CAIRO_FORMAT_A8	+ each pixel is a 8-bit quantity holding + an alpha value. (Since 1.0) +
CAIRO_FORMAT_A1	+ each pixel is a 1-bit quantity holding + an alpha value. Pixels are packed together into 32-bit + quantities. The ordering of the bits matches the + endianness of the platform. On a big-endian machine, the + first pixel is in the uppermost bit, on a little-endian + machine the first pixel is in the least-significant bit. (Since 1.0) +
CAIRO_FORMAT_RGB16_565	+ each pixel is a 16-bit quantity + with red in the upper 5 bits, then green in the middle + 6 bits, and blue in the lower 5 bits. (Since 1.2) +
CAIRO_FORMAT_RGB30	+ like RGB24 but with 10bpc. (Since 1.12) +

Since: 1.0

Image Surfaces

Functions

Types and Values

Description

Functions

cairo_format_stride_for_width ()

Parameters

Returns

cairo_image_surface_create ()

Parameters

Returns

cairo_image_surface_create_for_data ()

Parameters

Returns

cairo_image_surface_get_data ()

Parameters

Returns

cairo_image_surface_get_format ()

Parameters

Returns

cairo_image_surface_get_width ()

Parameters

Returns

cairo_image_surface_get_height ()

Parameters

Returns

cairo_image_surface_get_stride ()

Parameters

Returns

Types and Values

CAIRO_HAS_IMAGE_SURFACE

enum cairo_format_t

Members

See Also