The Logical Screen Descriptor component of a Graphics Interchange Format
stream.
See http://www.w3.org/Graphics/GIF/spec-gif89a.txt section 18.
Declaration Syntax| C# | Visual Basic | Visual C++ |
public class LogicalScreenDescriptor : GifComponent
Public Class LogicalScreenDescriptor _ Inherits GifComponent
public ref class LogicalScreenDescriptor : public GifComponent
Members| All Members | Constructors | Methods | Properties | ||
| Icon | Member | Description |
|---|---|---|
 | LogicalScreenDescriptor(Size, Boolean, Int32, Boolean, Int32, Int32, Int32) |
Constructor.
|
 | BackgroundColourIndex |
Gets the index into the Global Color Table for the Background Color.
The Background Color is the color used for those pixels on the
screen that are not covered by an image.
If the Global Color Table Flag is set to (zero), this field should
be zero and should be ignored.
|
| ColourResolution |
Gets the number of bits per primary color available to the original
image, minus 1. This value represents the size of the entire palette
from which the colors in the graphic were selected, not the number
of colors actually used in the graphic.
For example, if the value in this field is 3, then the palette of
the original image had 4 bits per primary color available to create
the image. This value should be set to indicate the richness of
the original palette, even if not every color from the whole
palette is available on the source machine.
|
| ComponentStatus |
Gets the status of this component, consisting of its error state
and any associated error message.
(Inherited from GifComponent.) |
| ConsolidatedState |
Gets the combined error states of this component and all its child
components.
(Inherited from GifComponent.) |
| Equals(Object) | (Inherited from Object.) |
| ErrorMessage |
Gets any error message associated with the component's error state.
(Inherited from GifComponent.) |
| ErrorState |
Gets the member of the Gif.Components.ErrorState enumeration held
within the ComponentStatus property.
(Inherited from GifComponent.) |
 | Finalize()()() | Allows an Object to attempt to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.) |
 | FromStream(Stream) |
Reads and returns a logical screen descriptor from the supplied
input stream.
|
| GetHashCode()()() | Serves as a hash function for a particular type. GetHashCode()()() is suitable for use in hashing algorithms and data structures like a hash table. (Inherited from Object.) |
| GetType()()() | Gets the Type of the current instance. (Inherited from Object.) |
| GlobalColourTableIsSorted |
Indicates whether the Global Color Table is sorted.
If the flag is set, the Global Color Table is sorted, in order of
decreasing importance. Typically, the order would be decreasing
frequency, with most frequent color first. This assists a decoder,
with fewer available colors, in choosing the best subset of colors;
the decoder may use an initial segment of the table to render the
graphic.
|
| GlobalColourTableSize |
Gets the number of colours in the global colour table.
|
| GlobalColourTableSizeBits |
If the Global Color Table Flag is set to 1, the value in this field
is used to calculate the number of bytes contained in the Global
Color Table. To determine that actual size of the color table,
raise 2 to [the value of the field + 1].
Even if there is no Global Color Table specified, set this field
according to the above formula so that decoders can choose the best
graphics mode to display the stream in.
|
| HasGlobalColourTable |
Gets a flag indicating the presence of a Global Color Table; if the
flag is set, the Global Color Table will immediately follow the
Logical Screen Descriptor. This flag also selects the interpretation
of the Background Color Index; if the flag is set, the value of the
Background Color Index field should be used as the table index of
the background color.
|
| LogicalScreenSize |
Gets the width and height, in pixels, of the logical screen where
the images will be rendered in the displaying device.
|
| MemberwiseClone()()() | Creates a shallow copy of the current Object. (Inherited from Object.) |
| PixelAspectRatio |
Gets the factor used to compute an approximation of the aspect ratio
of the pixel in the original image. If the value of the field is
not 0, this approximation of the aspect ratio is computed based on
the formula:
Aspect Ratio = (Pixel Aspect Ratio + 15) / 64
The Pixel Aspect Ratio is defined to be the quotient of the pixel's
width over its height. The value range in this field allows
specification of the widest pixel of 4:1 to the tallest pixel of
1:4 in increments of 1/64th.
|
| SetStatus(ErrorState, String) |
Sets the ComponentStatus property of thie GifComponent.
(Inherited from GifComponent.) |
| TestState(ErrorState) |
Tests whether the error state of this component or any of its member
components contains the supplied member of the ErrorState
enumeration.
(Inherited from GifComponent.) |
| ToString()()() |
Gets a string representation of the error status of this component
and its subcomponents.
(Inherited from GifComponent.) |
| WriteToStream(Stream) |
Writes this component to the supplied output stream.
(Overrides GifComponent.WriteToStream(Stream).) |
Remarks
The Logical Screen Descriptor contains the parameters necessary to
define the area of the display device within which the images will be
rendered. The coordinates in this block are given with respect to the
top-left corner of the virtual screen; they do not necessarily refer to
absolute coordinates on the display device. This implies that they
could refer to window coordinates in a window-based environment or
printer coordinates when a printer is used.
This block is REQUIRED; exactly one Logical Screen Descriptor must be
present per Data Stream.
Inheritance Hierarchy| Object | ||
 | GifComponent | |
| LogicalScreenDescriptor | |