Intel® 865G/865GV Chipset Datasheet - download.intel.nl - Intel

Functional DescriptionDepth-BiasThe GMCH supports source depth biasing in the setup engine, the depth bias value is specified inthe vertex command packet on a per primitive basis. The value ranges from -1 to 1. The depth biasvalue is added to the z or w value of the vertices. This is used for coplanar polygon priority. If twopolygons are to be rendered that are coplanar, due to the inherent precision differences induced byunique x, y and z values, there is no guarantee which polygon will be closer or farther. By usingdepth bias, it is possible to offset the destination z value (compare value) before comparing withthe new z value.Backface CullingAs part of the setup, the GMCH discards polygons from further processing, if they are facing awayfrom or towards the user’s viewpoint. This operation, referred to as “Back Face Culling” isaccomplished based on the “clockwise” or “counter-clockwise” orientation of the vertices on aprimitive. This can be enabled or disabled by the driver. This is referred to as “Back Face Culling.”5.4.1.2 Scan ConverterThe Scan Converter takes the vertex and edge information that is used to identify all pixels that areaffected by features being rendered. It works on a per-polygon basis.Pixel Rasterization RulesThe GMCH supports both OpenGL and D3D pixel rasterization rules to determine whether a pixelis filled by the triangle or line. For both D3D and OpenGL modes, a top-left filling convention forfilling geometry is used. Pixel rasterization rule on rectangle primitive is also supported using thetop-left fill convention.5.4.1.3 2D FunctionalityThe stretch BLT function can stretch source data in the X and Y directions to a destination larger orsmaller than the source. Stretch BLT functionality expands a region of memory into a larger orsmaller region using replication and interpolation. The stretch BLT function also provides formatconversion and data alignment.5.4.1.4 Texture EngineThe GMCH allows an image, pattern, or video to be placed on the surface of a 3D polygon. Thetexture processor receives the texture coordinate information from the setup engine and the textureblend information from the scan converter. The texture processor performs texture color orChromaKey matching, texture filtering (anisotropic, trilinear and bilinear interpolation), andYUV-to-RGB conversions.Perspective Correct Texture SupportA textured polygon is generated by mapping a 2D texture pattern onto each pixel of the polygon. Atexture map is like wallpaper pasted onto the polygon. Since polygons are rendered in perspective,it is important that texture be mapped in perspective as well. Without perspective correction,texture is distorted when an object recedes into the distance.166 Intel ® 82865G/82865GV GMCH Datasheet