Image Surfaces

Image Surfaces — Rendering to memory buffers

Synopsis




enum        cairo_format_t;
cairo_surface_t* cairo_image_surface_create (cairo_format_t format,
                                             int width,
                                             int height);
cairo_surface_t* cairo_image_surface_create_for_data
                                            (unsigned char *data,
                                             cairo_format_t format,
                                             int width,
                                             int height,
                                             int stride);
unsigned char* cairo_image_surface_get_data (cairo_surface_t *surface);
cairo_format_t cairo_image_surface_get_format
                                            (cairo_surface_t *surface);
int         cairo_image_surface_get_width   (cairo_surface_t *surface);
int         cairo_image_surface_get_height  (cairo_surface_t *surface);
int         cairo_image_surface_get_stride  (cairo_surface_t *surface);

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.

Details

enum cairo_format_t

typedef enum _cairo_format {
    CAIRO_FORMAT_ARGB32,
    CAIRO_FORMAT_RGB24,
    CAIRO_FORMAT_A8,
    CAIRO_FORMAT_A1,
    CAIRO_FORMAT_RGB16_565
} cairo_format_t;

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

New entries may be added in future versions.

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.)
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.
CAIRO_FORMAT_A8 each pixel is a 8-bit quantity holding an alpha value.
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 endianess 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.
CAIRO_FORMAT_RGB16_565 This format value is deprecated. It has never been properly implemented in cairo and should not be used by applications. For example, any attempt to create an image surface with a format of CAIRO_FORMAT_RGB16_565 will fail. This format value was added as part of fixing cairo's xlib backend to work with X servers advertising a 16-bit, 565 visual. But as it turned out, adding this format to cairo_format_t was not necessary, and was a mistake, (cairo's xlib backend can work fine with 16-bit visuals in the same way it works with BGR visuals without any BGR formats in cairo_format_t). (Since 1.2)

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 all 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).

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.

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 buffer will be used as the inital image contents; you must explicitely clear the buffer, using, for example, cairo_rectangle() and cairo_fill() if you want it cleared.

data : a pointer to a buffer supplied by the application in which to write contents.
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. Having this be specified separate from width allows for padding at the end of rows, or for writing to a subportion of a larger image.
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. See cairo_surface_set_user_data() for a means of attaching a destroy-notification fallback to the surface if necessary.

cairo_image_surface_get_data ()

unsigned char* cairo_image_surface_get_data (cairo_surface_t *surface);

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

surface : a cairo_image_surface_t
Returns : a pointer to the image data of this surface or NULL if surface is not an image surface.

Since 1.2

cairo_image_surface_get_format ()

cairo_format_t cairo_image_surface_get_format
                                            (cairo_surface_t *surface);

Get the format of the surface.

surface : a cairo_image_surface_t
Returns : the format of the surface

Since 1.2

cairo_image_surface_get_width ()

int         cairo_image_surface_get_width   (cairo_surface_t *surface);

Get the width of the image surface in pixels.

surface : a cairo_image_surface_t
Returns : the width of the surface in pixels.

cairo_image_surface_get_height ()

int         cairo_image_surface_get_height  (cairo_surface_t *surface);

Get the height of the image surface in pixels.

surface : a cairo_image_surface_t
Returns : the height of the surface in pixels.

cairo_image_surface_get_stride ()

int         cairo_image_surface_get_stride  (cairo_surface_t *surface);

Get the stride of the image surface in bytes

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

Since 1.2