Gnome::Cairo::Surface

Base class for surfaces

Description

cairo_surface_t is the abstract type representing all different drawing targets that cairo can render to. The actual drawings are performed using a cairo context.

Most surface types allow accessing the surface without using Cairo functions. If you do this, keep in mind that it is mandatory that you call flush() before reading from or writing to the surface and that you must use mark-dirty() after modifying it.

Synopsis

Declaration

unit class Gnome::Cairo::Surface;
also is Gnome::N::TopLevelClassSupport;

Methods

new

:similar

Create a new surface that is as compatible as possible with an existing surface. For example the new surface will have the same device scale, fallback resolution and font options as other. Generally, the new surface will also use the same backend as other, unless that is not possible for some reason. The type of the returned surface may be examined with get-type().

Initially the surface contents are all 0 (transparent if contents have transparency, black otherwise.) Use create-similar-image() if you need an image surface which can be painted quickly to the target surface. Return value: a pointer to the newly allocated surface. The caller owns the surface and should call clear-object() when done with it.

multi method new (
  cairo_surface_t :$similar!,
  cairo_content_t :$content = CAIRO_CONTENT_COLOR,
  Int :$width = 32, Int :$height = 32
)

$similar; the surface where the new surface is created from
$content; used to describe the content of a surface
$width; width of the image
$height; height of the image

:image

Create a new image surface that is as compatible as possible for uploading to and the use in conjunction with an existing surface. However, this surface can still be used like any normal image surface. Unlike new(:$similar) the new image surface won’t inherit the device scale from the $image surface.

Initially the surface contents are all 0 (transparent if contents have transparency, black otherwise.) Use new(:similar) if you don’t need an image surface.

multi method new (
  cairo_surface_t :image!, cairo_format_t :$format = CAIRO_FORMAT_RGB24,
  Int :$width = 32, Int :$height = 32
)

$image; the surface where the new surface is created from
$format; used to identify the memory format of image
$width; width of the image
$height; height of the image

:target

Create a new surface that is a rectangle within the target surface. All operations drawn to this surface are then clipped and translated onto the target surface. Nothing drawn via this sub-surface outside of its bounds is drawn onto the target surface, making this a useful method for passing constrained child surfaces to library routines that draw directly onto the parent surface, i.e. with no further backend allocations, double buffering or copies.

The semantics of subsurfaces have not been finalized yet unless the rectangle is in full device units, is contained within the extents of the target surface, and the target or subsurface’s device transforms are not changed.

multi method new (
  cairo_surface_t :$target,
  Num() :$x = 0e0, Num() :$y = 0e0,
  Num() :$width = 128e0, Num() :$height = 128e0
  --> cairo_surface_t
}

$target; the surface where the new surface is created from
$x, $y, $width and $height describe the rectangle from which a part of the image is copied.

:map, :rectangle

Creates an image surface that is the most efficient mechanism for modifying the backing store of the target surface. The region retrieved may be limited to the extents or Any for the whole surface.

Note, the use of the original surface as a target or source whilst it is mapped is undefined. The result of mapping the surface multiple times is also undefined. Calling clear-object() on the resulting image surface results in undefined behavior. Furthermore, changing the device transform of the image surface or of surface before the image surface is unmapped results in undefined behavior.

The caller must use unmap-image() to destroy this image surface. This function always creates a valid native object, but this class will become invalid if $map is already in an error state or any other error occurs. If the returned pointer does not have an error status, it is guaranteed to be an image surface whose format is not CAIRO_FORMAT_INVALID.

multi method new (
  cairo_surface_t :$map, cairo_rectangle_int_t :$rectangle
)

$map; the surface where the new surface is created from
$rectangle; an existing surface used to extract the image

:native-object

Create a Gnome::Cairo::Surface object using a native object from elsewhere. See also Gnome::N::TopLevelClassSupport.

multi method new ( N-GObject :$native-object! )

copy-page

Emits the current page for backends that support multiple pages, but doesn’t clear it, so that the contents of the current page will be retained for the next page. Use show-page() if you want to get an empty page after the emission. There is a convenience function for this that takes a cairo_t, namely copy-page().

method copy-page ( )

flush

Do any pending drawing for the surface and also restore any temporary modifications cairo has made to the surface’s state.

If the surface doesn’t support direct access, then this function does nothing.

method flush ( )

get-content

This function returns the content type of surface which indicates whether the surface contains color and/or alpha information. See cairo_content_t.

Return value: The content type of surface.

method get-content ( --> cairo_content_t )

get-device

This function returns the device for a surface. See cairo_device_t.

Return value: The device for surface or Any if the surface does not have an associated device.

method get-device ( --> cairo_device_t )

get-device-offset

This function returns the previous device offset set by set-device-offset().

method get-device-offset ( --> List )

List returns

Num; the offset in the X direction, in device units
Num; the offset in the Y direction, in device units

get-device-scale

This function returns the previous device offset set by set-device-scale().

method get-device-scale ( --> List )

List returns

Num; the scale in the X direction, in device units
Num; the scale in the Y direction, in device units

get-fallback-resolution

This function returns the previous fallback resolution set by set-fallback-resolution(), or default fallback resolution if never set.

method get-fallback-resolution ( --> List )

List returns

Num; horizontal pixels per inch
Num; vertical pixels per inch

get-font-options

Retrieves the default font rendering options for the surface. This allows display surfaces to report the correct subpixel order for rendering on them, print surfaces to disable hinting of metrics and so forth. The result can then be used with scaled-font-create().

method get-font-options ( --> Gnome::Cairo::FontOptions )

cairo_font_options_t $options; a cairo_surface_t

get-type

This function returns the type of the backend used to create a surface. See cairo_surface_type_t for available types. Return value: The type of surface.

method get-type ( --> cairo_surface_type_t )

has-show-text-glyphs

Returns whether the surface supports sophisticated show-text-glyphs() operations. That is, whether it actually uses the provided text and cluster data to a show-text-glyphs() call.

Note: Even if this function returns False, a show-text-glyphs() operation targeted at surface will still succeed. It just will act like a show-glyphs() operation.

Users can use this function to avoid computing UTF-8 text and cluster mapping if the target surface does not use it.

Return value: True if surface supports show-text-glyphs(), False otherwise.

method has-show-text-glyphs ( --> Bool )

mark-dirty

Tells cairo that drawing has been done to surface using means other than cairo, and that cairo should reread any cached areas. Note that you must call flush() before doing such drawing.

method mark-dirty ( )

mark-dirty-rectangle

Like mark-dirty(), but drawing has been done only to the specified rectangle, so that cairo can retain cached contents for other parts of the surface. Any cached clip set on the surface will be reset by this function, to make sure that future cairo calls have the clip set that they expect.

method mark-dirty-rectangle (
  Int $x, Int $y, Int $width, Int $height
)

$x; X coordinate of dirty rectangle
$y; Y coordinate of dirty rectangle
$width; width of dirty rectangle
$height; height of dirty rectangle

set-device-offset

Sets an offset that is added to the device coordinates determined by the CTM when drawing to surface. One use case for this function is when we want to create a cairo_surface_t that redirects drawing for a portion of an onscreen surface to an offscreen surface in a way that is completely invisible to the user of the cairo API. Setting a transformation via translate() isn’t sufficient to do this, since functions like device-to-user() will expose the hidden offset. Note that the offset affects drawing to the surface as well as using the surface in a source pattern.

method set-device-offset ( Num() $x_offset, Num() $y_offset )

$x_offset; the offset in the X direction, in device units
$y_offset; the offset in the Y direction, in device units

set-device-scale

Sets a scale that is multiplied to the device coordinates determined by the CTM when drawing to surface. One common use for this is to render to very high resolution display devices at a scale factor, so that code that assumes 1 pixel will be a certain size will still work. Setting a transformation via translate() isn’t sufficient to do this, since functions like device-to-user() will expose the hidden scale. Note that the scale affects drawing to the surface as well as using the surface in a source pattern.

method set-device-scale ( Num() $x_scale, Num() $y_scale )

$x_scale; a scale factor in the X direction
$y_scale; a scale factor in the Y direction

set-fallback-resolution

Set the horizontal and vertical resolution for image fallbacks. When certain operations aren’t supported natively by a backend, cairo will fallback by rendering operations to an image and then overlaying that image onto the output. For backends that are natively vector-oriented, this function can be used to set the resolution used for these image fallbacks, (larger values will result in more detailed images, but also larger file sizes). Some examples of natively vector-oriented backends are the ps, pdf, and svg backends. For backends that are natively raster-oriented, image fallbacks are still possible, but they are always performed at the native device resolution. So this function has no effect on those backends. Note: The fallback resolution only takes effect at the time of completing a page (with show-page() or copy-page()) so there is currently no way to have more than one fallback resolution in effect on a single page. The default fallback resoultion is 300 pixels per inch in both dimensions.

method set-fallback-resolution (
  Num() $x_pixels_per_inch, Num() $y_pixels_per_inch
)

$x_pixels_per_inch; horizontal setting for pixels per inch
$y_pixels_per_inch; vertical setting for pixels per inch

show-page

Emits and clears the current page for backends that support multiple pages. Use copy-page() if you don’t want to clear the page. There is a convenience function for this that takes a cairo_t, namely show-page().

method show-page ( )

status

Checks whether an error has previously occurred for this surface. Return value can be one of: CAIRO_STATUS_SUCCESS, CAIRO_STATUS_NULL_POINTER, CAIRO_STATUS_NO_MEMORY, CAIRO_STATUS_READ_ERROR, CAIRO_STATUS_INVALID_CONTENT, CAIRO_STATUS_INVALID_FORMAT, or CAIRO_STATUS_INVALID_VISUAL.

method status ( --> cairo_status_t )

unmap-image

Unmaps the image surface as returned from map-to-image()>. The content of the image will be uploaded to the target surface. Afterwards, the image is destroyed. Using an image surface which wasn’t returned by map-to-image() results in undefined behavior.

method unmap-image ( cairo_surface_t $image )

$image; the currently mapped image

write-to-png

Writes the contents of surface to a new file filename as a PNG image.

method write-to-png ( Str $filename --> cairo_status_t )

$filename; PNG Support

Gnome::Cairo::Surface

Description

See Also

Synopsis

Declaration

Methods

new

:similar

:image

:target

:map, :rectangle

:native-object

copy-page

flush

get-content

get-device

get-device-offset

get-device-scale

get-fallback-resolution

get-font-options

get-type

has-show-text-glyphs

mark-dirty

mark-dirty-rectangle

set-device-offset

set-device-scale

set-fallback-resolution

show-page

status

unmap-image

write-to-png