Labels:text | font | letter | screenshot | black and white | document OCR: VIRGE Integrated 3D Accelerator 83 Incorporated Filtering of 8 bits/pixel palettized data produces uncertain results. Palettized texel colors can be used if the filter mode is MITPP or 1TPP Ionly one texel is used to generale the color'} and the texture blending mode (lightingl is specified a5 decal, This means the texel color replaces the source pixel color ino mixing). Because the color is now palettized, it cannot be texture lit, fogged or alpha blended. 15.4.8.2 Generation ViRGE provides several compact texture storage modes, called Blend4 lhigh and low nibble) and Alpha4/Blend4. Blend4 uses 4 bits to define the color for each texel. These bits can be in either the high or low nibble of each byte, allowing the programmer to locate texels from two different textures in a single byte. Alpha4/Blend4 has 4 bits of Alpha coding and 4 bits of RGB color coding in each byte. Blend4 is useful for textures with a narrow range of colors, such as grass. The 4-bit value is an interpolation factor between two RGB colors defined in the Color 0 (MMB4FB) and Color1 (MM84FC) registers. Alpha4/Blend4 is useful for textures with a limited range of colors and transparency, such as a cloudy sky. In this case, there are a few shades of blue white, with whiter clouds being more opaque than bluer sky. Alpha blending is explained below. Generation of colors for Blend4 modes occurs after the filter phase. Therefore it is possible to filter multiple Blend4 texels to produce a composite color interpolation factor to be used in the generate phase. The results of this might be hard to predict. The filter phase can be bypassed by selecting a 1TPP filter mode. 15.4.8.3 Lighting Lighting Is the blending of the texel color with the source pixel color. As seen in Figure 15-7, it is used only when a lit triangle is specified in bits 30 27 of the Command Set register. Bits 16-15 of the Command Set register specify the blending modes as follows: 00 = Complex reflection 01 = Modulate 10 - Decal 11 - Reserved Complex reflection adds the (normalized, 0 = black and 1 = whitel texel and pixel colors, with a maximum value of 1. This lightens the pixel. Modulate multiplies the normalized color values. This results in a smaller value [darker pixell. The programmer may need to compensate for this darkening effect. Decal replaces the source pixel color with the texel color, essentially overlaying the texture on the scene. This is the only mode that can be used with palettized data. If the texture map is smaller than the area to be textured, texture wrapping can be turned on via bit 26 of the Command Set register. This allows the texture lo be tiled across the scene. If texture wrapping is disabled and and the texture map is smaller than the area to be textured, the texel color is taken from the Texture Border Color register (MMB4FO) for all pixels beyond the texture. ENHANCED PROGRAMMING 15-29
(.png)
