2.2.2.4.10.1.15 BoundsData
The BoundsData structure describes a rectangular area. It encodes (x,y) values that are based on changes from the previous rectangular position. Each value can be either a 16-bit absolute value or an 8-bit delta value, depending on the amount of change that took place.
The first byte of the BoundsData structure represents a set of flags that specify the type of data that is contained in the BoundsData structure. The flag can represent either an absolute (16-bit) or delta (8-bit) value for each x or y value that is supplied. If the flag is not set, then that x or y value is not present in the BoundsData array. The possible flags are specified below.
For each boundary value, either an 8-bit delta or a 16-bit absolute value MAY be specified. The two possible forms of representation MUST NOT be specified at the same time for any particular boundary. For example, if X_DELTA_LEFT is present, X_ABSOLUTE_LEFT MUST NOT be present.
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flags |
X_ABSOLUTE_LEFT (optional) |
Y_ABSOLUTE_TOP (optional) |
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... |
X_ABSOLUTE_RIGHT (optional) |
Y_ABSOLUTE_BOTTOM (optional) |
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... |
X_DELTA_LEFT (optional) |
Y_DELTA_TOP (optional) |
X_DELTA_RIGHT (optional) |
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Y_DELTA_BOTTOM (optional) |
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flags (1 byte): A set of flags that has one or more of the following bits set. The flag can represent either an absolute (16-bit) or delta (8-bit) value for each x or y value that is supplied. If a flag is not set, that x or y value is not present in the BoundsData array.
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The two possible forms of representation MUST NOT be specified at the same time for any particular boundary. For example, if bit A is enabled, bit E MUST NOT be enabled.
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0
1
2
3
4
5
6
7H
G
F
E
D
C
B
A
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Where the bits are defined as:
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Value
Description
A
X_ABSOLUTE_LEFT
A 16-bit x (left) value is present.
B
Y_ABSOLUTE_TOP
A 16-bit y (top) value is present.
C
X_ABSOLUTE_RIGHT
A 16-bit x (right) value is present.
D
Y_ABSOLUTE_BOTTOM
A 16-bit y (bottom) value is present.
E
X_DELTA_LEFT
An 8-bit x (left) value is present.
F
Y_DELTA_TOP
An 8-bit y (top) value is present.
G
X_DELTA_RIGHT
An 8-bit x (right) value is present.
H
Y_DELTA_BOTTOM
An 8-bit y (bottom) value is present.
X_ABSOLUTE_LEFT (2 bytes): A 16-bit x (left) value. Present when bit A is set in the flags field.
Y_ABSOLUTE_TOP (2 bytes): A 16-bit y (top) value. Present when bit B is set in the flags field.
X_ABSOLUTE_RIGHT (2 bytes): A 16-bit x (right) value. Present when bit C is set in the flags field.
Y_ABSOLUTE_BOTTOM (2 bytes): A 16-bit y (bottom) value. Present when bit D is set in the flags field.
X_DELTA_LEFT (1 byte): An 8-bit x (left) value. Present when bit E is set in the flags field.
Y_DELTA_TOP (1 byte): An 8-bit y (top) value. Present when bit F is set in the flags field.
X_DELTA_RIGHT (1 byte): An 8-bit x (right) value. Present when bit G is set in the flags field.
Y_DELTA_BOTTOM (1 byte): An 8-bit y (bottom) value. Present when bit H is set in the flags field.