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Visuals

Visuals — Low-level display hardware information

Types and Values

Object Hierarchy

    GObject
    ╰── GdkVisual

Includes

#include <gdk/gdk.h>

Description

A GdkVisual describes a particular video hardware display format. It includes information about the number of bits used for each color, the way the bits are translated into an RGB value for display, and the way the bits are stored in memory. For example, a piece of display hardware might support 24-bit color, 16-bit color, or 8-bit color; meaning 24/16/8-bit pixel sizes. For a given pixel size, pixels can be in different formats; for example the “red” element of an RGB pixel may be in the top 8 bits of the pixel, or may be in the lower 4 bits.

There are several standard visuals. The visual returned by gdk_screen_get_system_visual() is the system’s default visual, and the visual returned by gdk_screen_get_rgba_visual() should be used for creating windows with an alpha channel.

A number of functions are provided for determining the “best” available visual. For the purposes of making this determination, higher bit depths are considered better, and for visuals of the same bit depth, GDK_VISUAL_PSEUDO_COLOR is preferred at 8bpp, otherwise, the visual types are ranked in the order of(highest to lowest) GDK_VISUAL_DIRECT_COLOR, GDK_VISUAL_TRUE_COLOR, GDK_VISUAL_PSEUDO_COLOR, GDK_VISUAL_STATIC_COLOR, GDK_VISUAL_GRAYSCALE, then GDK_VISUAL_STATIC_GRAY.

Functions

gdk_query_depths ()

void
gdk_query_depths (gint **depths,
                  gint *count);

This function returns the available bit depths for the default screen. It’s equivalent to listing the visuals (gdk_list_visuals()) and then looking at the depth field in each visual, removing duplicates.

The array returned by this function should not be freed.

Parameters

depths

return location for available depths.

[out][array length=count][transfer none]

count

return location for number of available depths

 

gdk_query_visual_types ()

void
gdk_query_visual_types (GdkVisualType **visual_types,
                        gint *count);

This function returns the available visual types for the default screen. It’s equivalent to listing the visuals (gdk_list_visuals()) and then looking at the type field in each visual, removing duplicates.

The array returned by this function should not be freed.

Parameters

visual_types

return location for the available visual types.

[out][array length=count][transfer none]

count

return location for the number of available visual types

 

gdk_list_visuals ()

GList *
gdk_list_visuals (void);

Lists the available visuals for the default screen. (See gdk_screen_list_visuals()) A visual describes a hardware image data format. For example, a visual might support 24-bit color, or 8-bit color, and might expect pixels to be in a certain format.

Call g_list_free() on the return value when you’re finished with it.

Returns

a list of visuals; the list must be freed, but not its contents.

[transfer container][element-type GdkVisual]


gdk_visual_get_bits_per_rgb ()

gint
gdk_visual_get_bits_per_rgb (GdkVisual *visual);

gdk_visual_get_bits_per_rgb has been deprecated since version 3.22. and should not be used in newly-written code.

Use gdk_visual_get_red_pixel_details() and its variants to learn about the pixel layout of TrueColor and DirectColor visuals

Returns the number of significant bits per red, green and blue value.

Not all GDK backend provide a meaningful value for this function.

Parameters

visual

a GdkVisual

 

Returns

The number of significant bits per color value for visual .

Since: 2.22


gdk_visual_get_blue_pixel_details ()

void
gdk_visual_get_blue_pixel_details (GdkVisual *visual,
                                   guint32 *mask,
                                   gint *shift,
                                   gint *precision);

Obtains values that are needed to calculate blue pixel values in TrueColor and DirectColor. The “mask” is the significant bits within the pixel. The “shift” is the number of bits left we must shift a primary for it to be in position (according to the "mask"). Finally, "precision" refers to how much precision the pixel value contains for a particular primary.

Parameters

visual

a GdkVisual

 

mask

A pointer to a guint32 to be filled in, or NULL.

[out][allow-none]

shift

A pointer to a gint to be filled in, or NULL.

[out][allow-none]

precision

A pointer to a gint to be filled in, or NULL.

[out][allow-none]

Since: 2.22


gdk_visual_get_byte_order ()

GdkByteOrder
gdk_visual_get_byte_order (GdkVisual *visual);

gdk_visual_get_byte_order has been deprecated since version 3.22 and should not be used in newly-written code.

This information is not useful

Returns the byte order of this visual.

The information returned by this function is only relevant when working with XImages, and not all backends return meaningful information for this.

Parameters

visual

A GdkVisual.

 

Returns

A GdkByteOrder stating the byte order of visual .

Since: 2.22


gdk_visual_get_colormap_size ()

gint
gdk_visual_get_colormap_size (GdkVisual *visual);

gdk_visual_get_colormap_size has been deprecated since version 3.22 and should not be used in newly-written code.

This information is not useful, since GDK does not provide APIs to operate on colormaps.

Returns the size of a colormap for this visual.

You have to use platform-specific APIs to manipulate colormaps.

Parameters

visual

A GdkVisual.

 

Returns

The size of a colormap that is suitable for visual .

Since: 2.22


gdk_visual_get_depth ()

gint
gdk_visual_get_depth (GdkVisual *visual);

Returns the bit depth of this visual.

Parameters

visual

A GdkVisual.

 

Returns

The bit depth of this visual.

Since: 2.22


gdk_visual_get_green_pixel_details ()

void
gdk_visual_get_green_pixel_details (GdkVisual *visual,
                                    guint32 *mask,
                                    gint *shift,
                                    gint *precision);

Obtains values that are needed to calculate green pixel values in TrueColor and DirectColor. The “mask” is the significant bits within the pixel. The “shift” is the number of bits left we must shift a primary for it to be in position (according to the "mask"). Finally, "precision" refers to how much precision the pixel value contains for a particular primary.

Parameters

visual

a GdkVisual

 

mask

A pointer to a guint32 to be filled in, or NULL.

[out][allow-none]

shift

A pointer to a gint to be filled in, or NULL.

[out][allow-none]

precision

A pointer to a gint to be filled in, or NULL.

[out][allow-none]

Since: 2.22


gdk_visual_get_red_pixel_details ()

void
gdk_visual_get_red_pixel_details (GdkVisual *visual,
                                  guint32 *mask,
                                  gint *shift,
                                  gint *precision);

Obtains values that are needed to calculate red pixel values in TrueColor and DirectColor. The “mask” is the significant bits within the pixel. The “shift” is the number of bits left we must shift a primary for it to be in position (according to the "mask"). Finally, "precision" refers to how much precision the pixel value contains for a particular primary.

Parameters

visual

A GdkVisual

 

mask

A pointer to a guint32 to be filled in, or NULL.

[out][allow-none]

shift

A pointer to a gint to be filled in, or NULL.

[out][allow-none]

precision

A pointer to a gint to be filled in, or NULL.

[out][allow-none]

Since: 2.22


gdk_visual_get_visual_type ()

GdkVisualType
gdk_visual_get_visual_type (GdkVisual *visual);

Returns the type of visual this is (PseudoColor, TrueColor, etc).

Parameters

visual

A GdkVisual.

 

Returns

A GdkVisualType stating the type of visual .

Since: 2.22


gdk_visual_get_best_depth ()

gint
gdk_visual_get_best_depth (void);

Get the best available depth for the default GDK screen. “Best” means “largest,” i.e. 32 preferred over 24 preferred over 8 bits per pixel.

Returns

best available depth


gdk_visual_get_best_type ()

GdkVisualType
gdk_visual_get_best_type (void);

Return the best available visual type for the default GDK screen.

Returns

best visual type


gdk_visual_get_system ()

GdkVisual *
gdk_visual_get_system (void);

Get the system’s default visual for the default GDK screen. This is the visual for the root window of the display. The return value should not be freed.

Returns

system visual.

[transfer none]


gdk_visual_get_best ()

GdkVisual *
gdk_visual_get_best (void);

Get the visual with the most available colors for the default GDK screen. The return value should not be freed.

Returns

best visual.

[transfer none]


gdk_visual_get_best_with_depth ()

GdkVisual *
gdk_visual_get_best_with_depth (gint depth);

Get the best visual with depth depth for the default GDK screen. Color visuals and visuals with mutable colormaps are preferred over grayscale or fixed-colormap visuals. The return value should not be freed. NULL may be returned if no visual supports depth .

Parameters

depth

a bit depth

 

Returns

best visual for the given depth.

[transfer none]


gdk_visual_get_best_with_type ()

GdkVisual *
gdk_visual_get_best_with_type (GdkVisualType visual_type);

Get the best visual of the given visual_type for the default GDK screen. Visuals with higher color depths are considered better. The return value should not be freed. NULL may be returned if no visual has type visual_type .

Parameters

visual_type

a visual type

 

Returns

best visual of the given type.

[transfer none]


gdk_visual_get_best_with_both ()

GdkVisual *
gdk_visual_get_best_with_both (gint depth,
                               GdkVisualType visual_type);

Combines gdk_visual_get_best_with_depth() and gdk_visual_get_best_with_type().

Parameters

depth

a bit depth

 

visual_type

a visual type

 

Returns

best visual with both depth and visual_type , or NULL if none.

[nullable][transfer none]


gdk_visual_get_screen ()

GdkScreen *
gdk_visual_get_screen (GdkVisual *visual);

Gets the screen to which this visual belongs

Parameters

visual

a GdkVisual

 

Returns

the screen to which this visual belongs.

[transfer none]

Since: 2.2

Types and Values

GdkVisual

typedef struct _GdkVisual GdkVisual;

A GdkVisual contains information about a particular visual.


enum GdkVisualType

A set of values that describe the manner in which the pixel values for a visual are converted into RGB values for display.

Members

GDK_VISUAL_STATIC_GRAY

Each pixel value indexes a grayscale value directly.

 

GDK_VISUAL_GRAYSCALE

Each pixel is an index into a color map that maps pixel values into grayscale values. The color map can be changed by an application.

 

GDK_VISUAL_STATIC_COLOR

Each pixel value is an index into a predefined, unmodifiable color map that maps pixel values into RGB values.

 

GDK_VISUAL_PSEUDO_COLOR

Each pixel is an index into a color map that maps pixel values into rgb values. The color map can be changed by an application.

 

GDK_VISUAL_TRUE_COLOR

Each pixel value directly contains red, green, and blue components. Use gdk_visual_get_red_pixel_details(), etc, to obtain information about how the components are assembled into a pixel value.

 

GDK_VISUAL_DIRECT_COLOR

Each pixel value contains red, green, and blue components as for GDK_VISUAL_TRUE_COLOR, but the components are mapped via a color table into the final output table instead of being converted directly.

 

enum GdkByteOrder

A set of values describing the possible byte-orders for storing pixel values in memory.

Members

GDK_LSB_FIRST

The values are stored with the least-significant byte first. For instance, the 32-bit value 0xffeecc would be stored in memory as 0xcc, 0xee, 0xff, 0x00.

 

GDK_MSB_FIRST

The values are stored with the most-significant byte first. For instance, the 32-bit value 0xffeecc would be stored in memory as 0x00, 0xff, 0xee, 0xcc.

 
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