_DXVA_Highlight structure

Description

The DXVA_Highlight structure is sent by the host decoder to the accelerator to specify a highlighted rectangular area of a subpicture, and to create an alpha-blending surface with DCCMD data and a DPXD surface.

Members

wHighlightActive

Indicates whether a rectangular highlight area is active. Zero indicates inactive and 1 indicates active. If inactive, the highlight data must have no effect on the content of the blended picture.

wHighlightIndices

Contains four palette indexes. Each palette index consists of 4 bits. Each 2-bit index in the highlighted rectangular area of the DXPD is used to select among these four palette indexes. The 4 most significant bits are for index 3, the next 4 bits are for index 2, the next 4 bits are for index 1, and the 4 least significant bits are for index 0.

wHighlightAlphas

Contains four opacity values. Each opacity value consists of 4 bits. Each 2-bit index in the highlighted rectangular area of the DXPD is used to select among these four opacity values. The 4 most significant bits are for index 3, the next 4 bits are for index 2, the next 4 bits are for index 1, and the 4 least significant bits are for index 0.

These 4-bit opacity values are each referred to as a SampleAlpha4 variable and are interpreted as follows:

• The value zero indicates that the graphic content at the corresponding location is transparent (so that the palette entry indexed by the corresponding bits of wHighlightIndices has no effect on the resulting blended picture). For a zero value, the blend specified is to use the video picture content without alteration.
• The value 15 indicates that the graphic content at the corresponding location is opaque (so that the palette entry indexed by the corresponding bits of wHighlightIndices completely determines the resulting blended picture).
• For nonzero values, the specified blend is found using the following expression:
• ( ( ( (SampleAlpha4 + 1) x (graphic value) ) + ( ( (15 - SampleAlpha4) x (picture value) ) + 8 ) >> 4

HighlightRect

Specifies a RECT structure that defines the area of the highlight rectangle.

The following restrictions apply to the RECT dimensions:

• left and top must be greater than or equal to zero.
• right and bottom must be greater than left and top, respectively.
• right must not exceed 720, and bottom must not exceed 576.

Remarks

The DXVA_Highlight structure is formulated in a manner compatible with the DVD video specification as specified by the DVD Forum.

Note There is a difference between the way the DVD specification defines a subpicture rectangular area and the convention used by Microsoft. This section follows the Microsoft convention so a rectangle of width 10 and height 10 in the upper-left corner of the picture is defined by top = 0, left = 0, right = 10, bottom = 10. The DVD specification defines right = 9 and bottom = 9.

See also

RECT