Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0

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13.29.Programming Hints/Rules

The following provides programming hints/rules for 3D, Motion Compensation, and Stretch Blitter operations.

Drawing and Scissor Rectangles

Must declare a Drawing Rectangle packet first before Scissor Rectangle packet

Coordinates of Drawing Rectangle must be Xmax > Xmin and Ymax > Ymin

Drawing Rectangle width and height must be greater than 1pixel for Rectangle primitives.

Drawing Rectangle X & Y coordinates must be within the screen size. The drawing rectangle must be clipped to screen coordinates before send to hardware. However, the origin of the drawing rectangle can be negative since it is need not be clipped. It is the reference point (origin) of all the primitives and scissor rectangle that belong to the drawing rectangle.

Xmin, Ymin

0,0

Origin of

Scissor

Screen

Xmax, Ymax

scissor.vsd

Small Triangle Filter

Small Triangle Filter can only be enabled if the horizontal and vertical bias values (defined in Dest Buffer variable packet) are programmed to (0000,0000) or (1000,1000). This is corresponds to the pixel center of (0,0) and (0.5,0.5), respectively.

Mapping Engine Cache (MEC)

A Texture palette load must contain all 256 entries. Even if only one entry needs to be updated, all 256 entries in the Texture palette must be loaded using the texture palette load packet.

Color Key and Chroma Key cannot be enabled at the same time.

In mult-texture, Colorkey and Chromkey only compare with Map 0 texels and not on Map 1 texels.

Any programming change made to the Mapping Engine Cache Enable state variable must be followed by a 3D pipeline flush, otherwise pixel corruption will occur. For example, software changes the state of the Mapping Engine cache by flipping the bit Mapping Cache Enable using the

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Intel 815 manual Programming Hints/Rules, Drawing and Scissor Rectangles