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<!---======================= begin_copyright_notice ============================
Copyright (C) 2020-2021 Intel Corporation
SPDX-License-Identifier: MIT
============================= end_copyright_notice ==========================-->
## Opcode
3D_SAMPLE4 = 0x6f
## Format
### CONDITION
- Op.op=gather4
| | | | | | | |
| --- | --- | --- | --- | --- | --- | --- |
| 0x6f(3D_SAMPLE4) | Op | Exec_size | Pred | Src_channel | Aoffimmi | Sampler |
| | Surface | Dst | NumParams | U | V | R |
| | Ai\* | | | | | |
### CONDITION
- Op.op=gather4_c
| | | | | | | |
| --- | --- | --- | --- | --- | --- | --- |
| 0x6f(3D_SAMPLE4) | Op | Exec_size | Pred | Src_channel | Aoffimmi | Sampler |
| | Surface | Dst | NumParams | Ref\* | U | V |
| | R | Ai\* | | | | |
### CONDITION
- Op.op=gather4_po
| | | | | | | |
| --- | --- | --- | --- | --- | --- | --- |
| 0x6f(3D_SAMPLE4) | Op | Exec_size | Pred | Src_channel | Aoffimmi | Sampler |
| | Surface | Dst | NumParams | U | V | Offu\* |
| | Offv\* | R | | | | |
### CONDITION
- Op.op=gather4_po_c
| | | | | | | |
| --- | --- | --- | --- | --- | --- | --- |
| 0x6f(3D_SAMPLE4) | Op | Exec_size | Pred | Src_channel | Aoffimmi | Sampler |
| | Surface | Dst | NumParams | Ref\* | U | V |
| | Offu\* | Offv\* | R | | | |
## Semantics
Sample the surface using bilinear filtering, and return four samples.
## Description
Sample <surface> using bilinear filtering, and return four samples for each pixel in <dst>.
- **Op(ub):**
- Bit[4..0]: encodes the sampler operation
- 0b01000: gather4
- 0b10000: gather4_c
- 0b10001: gather4_po
- 0b10010: gather4_po_c
- Bit[5]: pixel null mask enable. Specifies whether the writeback message will include an extra phase indicating the pixel null mask.
- **Exec_size(ub):** Execution size
- Bit[2..0]: size of the region for source and destination operands
- 0b011: 8 elements
- 0b100: 16 elements
- Bit[7..4]: execution mask (explicit control over the enabled channels)
- 0b0000: M1
- 0b0001: M2
- 0b0010: M3
- 0b0011: M4
- 0b0100: M5
- 0b0101: M6
- 0b0110: M7
- 0b0111: M8
- 0b1000: M1_NM
- 0b1001: M2_NM
- 0b1010: M3_NM
- 0b1011: M4_NM
- 0b1100: M5_NM
- 0b1101: M6_NM
- 0b1110: M7_NM
- 0b1111: M8_NM
- **Pred(uw):** Predication control
- **Src_channel(ub):**
- Bit[1..0]: controls the source channel to be sampled
- 0b00: R
- 0b01: G
- 0b10: B
- 0b11: A
- **Aoffimmi(scalar):** A UW representing the _aoffimmi modifier with the following format:
- Bit[3..0]: stores the R offset. Valid values are [-8-7]
- Bit[7..4]: stores the V offset. Valid values are [-8-7]
- Bit[11..8]: stores the U offset. Valid values are [-8-7]
- Bit[15..12]: reserved. Must be zero
- **Sampler(ub):** Index of the sampler variable
- **Surface(ub):** Index of the surface variable
- **Dst(raw_operand):** The result of the sample. The four samples map to the RGBA channels as follows:. Must have type HF,F,W,UW,D,UD
+-------------------------+--------------------------+
| upper left sample = A | upper right sample = B |
+-------------------------+--------------------------+
| lower left sample = R | lower right sample = G |
+-------------------------+--------------------------+
- **NumParams(ub):** number of additional parameters for this instruction. Valid values are [1-15]
- **Ref(raw_operand):** The first <exec_size> elements contain the reference value that is compared against the red channel of the sampled surface
- **U(raw_operand):** The first <exec_size> elements contain the X pixel address
- **V(raw_operand):** The first <exec_size> elements contain for
- 1D_array surfaces: the unnormalized array index
- Other surface: the normalized y coordinate
- **Offu(raw_operand):** The first <exec_size> elements contain the pixel offset from U. Must have type D
- **Offv(raw_operand):** The first <exec_size> elements contain the pixel offset from V. Must have type D
- **R(raw_operand):** The first <exec_size> elements contain for
- 2D_array: the unnormalized array index.
- 3D and cube: the normalized z coordinate
- **Ai(raw_operand):** The first <exec_size> elements contain the array index for a cube surface
#### Properties
## Text
```
[(<P>)] SAMPLE4[.pixel_null_mask].<Src_channel> (Exec_size) <Aoffimmi> <Sampler> <Surface> <Dst> <u> <v> <r> <ai>
[(<P>)] SAMPLE4_C[.pixel_null_mask].<Src_channel> (Exec_size) <Aoffimmi> <Sampler> <Surface> <Dst> <ref> <u> <v> <r> <ai>
[(<P>)] SAMPLE4_PO[.pixel_null_mask].<Src_channel> (Exec_size) <Aoffimmi> <Sampler> <Surface> <Dst> <u> <v> <offu> <offv> <r>
[(<P>)] SAMPLE4_PO_C[.pixel_null_mask].<Src_channel> (Exec_size) <Aoffimmi> <Sampler> <Surface> <Dst> <ref> <u> <v> <offu> <offv> <r>
// instruction specific parameters may vary
```
## Notes
For each enabled channel <exec_size> elements are returned in RGBA order, with the disabled channels skipped in the results. Only the enabled pixels are returned in <dst>. Each channel's return data start in the next GRF; if <exec_size> * sizeof(dst_type) is smaller than the register size, the remaining portions of the register have undefined values.
For all operations, if <pixel_null_mask> is set, an additional GRF is returned after the sampler data, with <exec_size> bits in the first DWord containing the pixel null mask values. This field has the bit for all pixels set to 1 except those pixels in which a null page was source for at least one texel.
Extra parameters (after NumParams) for this instruction are required only for certain operations and surface types.
- **{pre-ICLLP}** All operands must have type F.
- **{ICLLP+}** All operands must have the same type, which can be either HF or F.
- It is permitted to skip the trailing parameters; the missing parameters will have the value of 0.
The table below summarizes the additional arguments for each of the sample4 operations.
+------------------+---------------------------------------------+
| Operation | Parameters |
| +------+-----+--------+--------+--------+-----+
| | 0 | 1 | 2 | 3 | 4 | 5 |
+------------------+------+-----+--------+--------+--------+-----+
| gather4 | u | v | r | ai | | |
+------------------+------+-----+--------+--------+--------+-----+
| gather4_c | ref | u | v | r | ai | |
+------------------+------+-----+--------+--------+--------+-----+
| gather4_po | u | v | offu | offv | r | |
+------------------+------+-----+--------+--------+--------+-----+
| gather4_po_c | ref | u | v | offu | offv | r |
+------------------+------+-----+--------+--------+--------+-----+
|
