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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.
Usually you can avoid thinking about visuals in GTK+. Visuals are useful to
interpret the contents of a GdkImage, but you should avoid GdkImage precisely
because its contents depend on the display hardware; use GdkPixbuf instead, for
all but the most low-level purposes. Also, anytime you provide a GdkColormap,
the visual is implied as part of the colormap (gdk_colormap_get_visual()), so
you won't have to provide a visual in addition.
There are several standard visuals. The visual returned
by gdk_visual_get_system() is the system's default
visual. gdk_rgb_get_visual() return the visual most
suited to displaying full-color image data. If you
use the calls in GdkRGB, you should create your windows
using this visual (and the colormap returned by
gdk_rgb_get_colormap()).
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.
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.
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.
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.
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.
GdkVisualType
gdk_visual_get_best_type (void);
Return the best available visual type for the default GDK screen.
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.
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.
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
.
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
.
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().
#define gdk_visual_ref(v) g_object_ref(v)
gdk_visual_ref is deprecated and should not be used in newly-written code.
Deprecated equivalent of g_object_ref().
#define gdk_visual_unref(v) g_object_unref(v)
gdk_visual_unref is deprecated and should not be used in newly-written code.
Deprecated equivalent of g_object_unref().
GdkScreen *
gdk_visual_get_screen (GdkVisual *visual);
Gets the screen to which this visual belongs
Since 2.2
gint
gdk_visual_get_bits_per_rgb (GdkVisual *visual);
Returns the number of significant bits per red, green and blue value.
Since 2.22
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.
Since 2.22
GdkByteOrder
gdk_visual_get_byte_order (GdkVisual *visual);
Returns the byte order of this visual.
Since 2.22
gint
gdk_visual_get_colormap_size (GdkVisual *visual);
Returns the size of a colormap for this visual.
Since 2.22
gint
gdk_visual_get_depth (GdkVisual *visual);
Returns the bit depth of this visual.
Since 2.22
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.
Since 2.22
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.
Since 2.22
GdkVisualType
gdk_visual_get_visual_type (GdkVisual *visual);
Returns the type of visual this is (PseudoColor, TrueColor, etc).
Since 2.22
typedef struct {
GObject parent_instance;
GdkVisualType GSEAL (type);
gint GSEAL (depth);
GdkByteOrder GSEAL (byte_order);
gint GSEAL (colormap_size);
gint GSEAL (bits_per_rgb);
guint32 GSEAL (red_mask);
gint GSEAL (red_shift);
gint GSEAL (red_prec);
guint32 GSEAL (green_mask);
gint GSEAL (green_shift);
gint GSEAL (green_prec);
guint32 GSEAL (blue_mask);
gint GSEAL (blue_shift);
gint GSEAL (blue_prec);
} GdkVisual;
The GdkVisual structure contains information about a particular visual.
Example 5. Constructing a pixel value from components
1 2 3 4 5 6 7 8 |
guint pixel_from_rgb (GdkVisual *visual, guchar r, guchar b, guchar g) { return ((r >> (16 - visual->red_prec)) << visual->red_shift) | ((g >> (16 - visual->green_prec)) << visual->green_shift) | ((r >> (16 - visual->blue_prec)) << visual->blue_shift); } |
A set of values that describe the manner in which the pixel values for a visual are converted into RGB values for display.
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Each pixel value indexes a grayscale value directly. |
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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. |
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Each pixel value is an index into a predefined, unmodifiable color map that maps pixel values into RGB values. |
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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. |
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Each pixel value directly contains red, green,
and blue components. The green_mask, and
blue_mask fields of the GdkVisual
structure describe how the components are assembled into a pixel value. |
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Each pixel value contains red, green, and blue
components as for |
A set of values describing the possible byte-orders for storing pixel values in memory.
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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. |
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The values are stored with the most-significant byte first. For instance, the 32-bit value 0xffeecc would be stored in memory as 0x00, 0xcc, 0xee, 0xff. |