texldl - ps

Sample a texture with a particular sampler. The particular mipmap level-of-detail being sampled has to be specified as the fourth component of the texture coordinate.

Syntax

Where:

• dst is a destination register.
• src0 is a source register that provides the texture coordinates for the texture sample. See Texture Coordinate Register.
• src1 identifies the source sampler register (s#), where # specifies which texture sampler number to sample. The sampler has associated with it a texture and a control state defined by the D3DSAMPLERSTATETYPE enumeration (for example, D3DSAMP_MINFILTER).

Remarks

texldl looks up the texture set at the sampler stage referenced by src1. The level-of-detail is selected from src0.w. This value can be negative in which case the level-of-detail selected is the zeroth one (biggest map) with the MAGFILTER. Since src0.w is a floating point value, the fractional value is used to interpolate (if MIPFILTER is LINEAR) between two mip levels. Sampler states MIPMAPLODBIAS and MAXMIPLEVEL are honored. For more information about sampler states, see D3DSAMPLERSTATETYPE.

If a shader program samples from a sampler that does not have a texture set, then 0001 is obtained in the destination register.

The following is a rough algorithm that the reference device follows:

LOD = src0.w + LODBIAS;
if (LOD <= 0 )
{
   LOD = 0;
   Filter = MagFilter;
   tex = Lookup( MAX(MAXMIPLEVEL, LOD), Filter );
}
else
{
   Filter = MinFilter;
   LOD = MAX( MAXMIPLEVEL, LOD );
   tex = Lookup( Floor(LOD), Filter );
   if( MipFilter == LINEAR )
   {
      tex1 = Lookup( Ceil(LOD), Filter );                        
      tex = (1 - frac(src0.w))*tex + frac(src0.w)*tex1;
   }
}

Restrictions:

• The texture coordinates should not be scaled by texture size.
• dst must be a Temporary Register (r#).
• dst can accept a writemask. See Destination Register Write Mask.
• Defaults for missing components are either 0 or 1, and depend on the texture format.
• src1 must be a Sampler (s#). src1 may not use a negate modifier (see Destination Register Write Mask). src1 may use swizzle (see Source Register Swizzling), which is applied after sampling, but before the write mask (see Destination Register Write Mask) is honored. The sampler must have been declared (using dcl_samplerType - ps) at the beginning of the shader.
• The number of coordinates required to perform the texture sample depends on how the sampler was declared. If it was declared as a cube, a three-component texture coordinate is required (.rgb). Validation enforces that coordinates provided to tex_ldl Are sufficient for the texture dimension declared for the sampler. However, it is not guaranteed that the application actually sets a texture (through the API) with dimensions equal to the dimension declared for the sampler. In such a case, the runtime will attempt to detect mismatches (possibly in debug only). Sampling a texture with fewer dimensions than are present in the texture coordinate will be allowed and assumed to ignore the extra texture coordinate components. Conversely, sampling a texture with more dimensions than are present in the texture coordinate is illegal.
• If the src0 (texture coordinate) is Temporary Register, the components required for the lookup (described above) must have been previously written.
• Sampling unsigned RGB textures will result in float values between 0.0 and 1.0.
• Sampling signed textures will result in float values between -1.0 to 1.0.
• When sampling floating-point textures, Float16 means that the data will range within MAX_FLOAT16. Float32 means the maximum range of the pipeline will be used. Sampling outside of either range is undefined.
• There is no dependent read limit.