gdk-Visuals {RGtk2} | R Documentation

## Visuals

### Description

Low-level display hardware information

### Methods and Functions

`gdkQueryDepths()`
`gdkQueryVisualTypes()`
`gdkListVisuals()`
`gdkVisualGetBestDepth()`
`gdkVisualGetBestType()`
`gdkVisualGetSystem()`
`gdkVisualGetBest()`
`gdkVisualGetBestWithDepth(depth)`
`gdkVisualGetBestWithType(visual.type)`
`gdkVisualGetBestWithBoth(depth, visual.type)`
`gdkVisualGetScreen(object)`

### Detailed 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.

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 (`gdkColormapGetVisual`), so you won't have to provide a visual in addition.

There are several standard visuals. The visual returned by `gdkVisualGetSystem` is the system's default visual. `gdkRgbGetVisual` 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 `gdkRgbGetColormap`).

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`.

### Structures

`GdkVisual`

  The `GdkVisual` structure contains information about a particular visual.

  `type`

    [`GdkVisualType`] inherited portion from `GObject`

  `depth`

    [integer] The type of this visual.

  `byteOrder`

    [`GdkByteOrder`] The number of bits per pixel.

  `colormapSize`

    [integer] The byte-order for this visual.

  `bitsPerRgb`

    [integer] The number of entries in the colormap, for visuals of type `GDK_VISUAL_PSEUDO_COLOR` or `GDK_VISUAL_GRAY_SCALE`. For other visual types, it is the number of possible levels per color component. If the visual has different numbers of levels for different components, the value of this field is undefined.

  `redMask`

    [numeric] The number of significant bits per red, green, or blue when specifying colors for this visual. (For instance, for `gdkColormapAllocColor`)

  `redShift`

    [integer] A mask giving the bits in a pixel value that correspond to the red field. Significant only for `GDK_VISUAL_PSEUDOCOLOR` and `GDK_VISUAL_DIRECTCOLOR`.

  `redPrec`

    [integer] The `red_shift` and `red_prec` give an alternate presentation of the information in `red_mask`. `red_mask` is a contiguous sequence of `red_prec` bits starting at bit number `red_shift`. For example, shows constructing a pixel value out of three 16 bit color values.

  `greenMask`

    [numeric] See above.

  `greenShift`

    [integer] A mask giving the bits in a pixel value that correspond to the green field.

  `greenPrec`

    [integer] The `green_shift` and `green_prec` give an alternate presentation of the information in `green_mask`.

  `blueMask`

    [numeric] See above.

  `blueShift`

    [integer] A mask giving the bits in a pixel value that correspond to the blue field.

  `bluePrec`

    [integer] The `blue_shift` and `blue_prec` give an alternate presentation of the information in `blue_mask`.

### Enums and Flags

`GdkVisualType`

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

  `static-gray`

    Each pixel value indexes a grayscale value directly.

  `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.

  `static-color`

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

  `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.

  `true-color`

    Each pixel value directly contains red, green, and blue components. The `red_mask`, `green_mask`, and `blue_mask` fields of the `GdkVisual` structure describe how the components are assembled into a pixel value.

  `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.

`GdkByteOrder`

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

  `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.

  `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, 0xcc, 0xee, 0xff.

### Author(s)

Derived by RGtkGen from GTK+ documentation

### References

https://developer-old.gnome.org/gdk2/stable/gdk2-Visuals.html

### See Also

`GdkImage` `GdkColormap`

[Package RGtk2 version 2.20.40 Index]