ld2dms (sm4.1 - asm)

Reads individual samples out of 2-dimensional multi-sample textures.

ld2dms[_aoffimmi(u,v)] dest[.mask], srcAddress[.swizzle], srcResource[.swizzle], sampleIndex (scalar operand)

 

ItemDescription

dest

[in] The address of result of the operation.

srcAddress

[in] The texture coordinates needed to perform the sample.

srcResource

[in] A texture register (t#) which must have been declared identifying which Texture or Buffer to fetch from

sampleIndex

[in] Idendifies the samples to read from srcResource.

 

Remarks

This instruction is a simplified alternative to the sample instruction. It fetches data from the specified Texture without any filtering (e.g. point sampling) using the provided integer srcAddress and sampleIndex.

srcAddress provides the set of texture coordinates needed to perform the sample in the form of unsigned integers. If srcAddress is out of the range[0...(#texels in dimension -1)], ld2dms always returns 0 in all components present in the format of the resource, and defaults (0,0,0,1.0f/0x00000001) for missing components.

sampleIndex does not have to be a literal. The multi-sample count does not have to be specified on the texture resource, and it works with depth or stencil views.

An application wishing any more flexible control over out-of-range address behavior should use the sample instruction instead, as it honors address wrap/mirror/clamp/border behavior defined as sampler state.

srcAddress.b (post-swizzle) is ignored for Texture2Ds. If the value is out of the range of available array indices [0...(array size-1)], then ld2dms always returns 0 in all components present in the format of the resource, and defaults (0,0,0,1.0f/0x00000001) for missing components.

For Texture2D Arrays, srcAddress.b (post-swizzle) provides the array index. Oherwise it has the same behavior as Texture2D.

srcAddress.a (post-swizzle) is always ignored. The HLSL compiler will never output anything there.

srcResource is a texture register (t#) which must have been declared(22.3.11), identifying which Texture to fetch from.

Fetching from t# that has nothing bound to it returns 0 for all components.

Address Offset

The optional [_aoffimmi(u,v,w)] suffix (address offset by immediate integer) indicates that the texture coordinates for the ld2dms are to be offset by a set of provided immediate texel space integer constant values. The literal values are a set of 4 bit 2's complement numbers, having integer range [-8,7].

The offsets are added to the texture coordinates, in texel space.

Address offsets are not applied along the array axis of Texture1D/2D Arrays.

The _aoffimmi v,w components are ignored for Texture1Ds.

The _aoffimmi w component is ignored for Texture2Ds.

Because the texture coordinates for ld2dms are unsigned integers, if the offset causes the address to go below zero, it will wrap to a large address, and result in an out of bounds access, which like ld returns 0 in all components present in the format of the resource, and the defaults (0,0,0,1.0f/0x00000001) for missing components.

Sample Number

ld2dms is available for use on any resource. ld2dms operates identically to ld except on 2D multsample resources, by using the additional (0-based) sampleIndex operand to identify which sample to read from the resource.

The result of specifying a sampleIndex that exceeds the number of samples in the resource is undefined, but cannot return data outside of the address space of the device context.

Return Type Control

The data format returned by ld2dms to the destination register is determined in the same way as described for the sample instruction. It is based on the format bound to the srcResource parameter (t#).

As with the sample instruction, returned values for ld2dms are 4-vectors with format-specific defaults for components not present in the format. The swizzle on srcResource determines how to swizzle the 4-component result coming back from the texture load, after which .mask on dest determines which components in dest get updated.

When a 32-bit float value is read by ld2dms into a 32-bit register, the bits are untouched; that is, denormal values remain denormal. This is unlike the sample instruction.

Miscellaneous Details

As there is no filtering associated with this instruction, concepts like LOD bias do not apply. Accordingly there is no sampler s# parameter.

Restrictions

  • srcResource must be a t# register, and not a TextureCube, Texture1D or Texture1DArray. srcResource cannot be a ConstantBuffer, which cannot be bound to t# registers.
  • Relative addressing on srcResource is not permitted.
  • srcAddress and sampleIndex must be a temp (r#/x#), constant (cb#) or input (v#) register.
  • dest must be a temp (r#/x#) or output (o*#) register.

This instruction applies to the following shader stages:

Vertex ShaderGeometry ShaderPixel Shader
xxx

 

Minimum Shader Model

This function is supported in the following shader models.

Shader ModelSupported
Shader Model 5 yes
Shader Model 4.1 yes
Shader Model 4 no
Shader Model 3 (DirectX HLSL) no
Shader Model 2 (DirectX HLSL) no
Shader Model 1 (DirectX HLSL) no

 

 

 

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