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[Merged by Bors] - Use 3 bits of PipelineKey to store MSAA sample count #5826

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[Merged by Bors] - Use 3 bits of PipelineKey to store MSAA sample count #5826

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lain-dono
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Sample count always power of two. Thus, it is enough to store log2(sample_count).
This can be implemented using u32::trailing_zeros. Then we can restore sample count with the 1 << stored.
You get 3 bits instead of 6 and up to 128x MSAA. This is more than is supported by any common hardware.

Full table of possible variations:

    original MSAA sample count      stored    loaded
* 00000000000000000000000000000000 -> 000 -> 00000001  1
  00000000000000000000000000000001 -> 000 -> 00000001  1
  00000000000000000000000000000010 -> 001 -> 00000010  2
  00000000000000000000000000000100 -> 010 -> 00000100  4
  00000000000000000000000000001000 -> 011 -> 00001000  8
  00000000000000000000000000010000 -> 100 -> 00010000  16
  00000000000000000000000000100000 -> 101 -> 00100000  32
  00000000000000000000000001000000 -> 110 -> 01000000  64
  00000000000000000000000010000000 -> 111 -> 10000000  128
* 00000000000000000000000100000000 -> 000 -> 00000001  256
* 00000000000000000000001000000000 -> 001 -> 00000010  512
* 00000000000000000000010000000000 -> 010 -> 00000100  1024
* 00000000000000000000100000000000 -> 011 -> 00001000  2048
* 00000000000000000001000000000000 -> 100 -> 00010000  4096
* 00000000000000000010000000000000 -> 101 -> 00100000  8192
* 00000000000000000100000000000000 -> 110 -> 01000000  16384
* 00000000000000001000000000000000 -> 111 -> 10000000  32768
* 00000000000000010000000000000000 -> 000 -> 00000001  65536
* 00000000000000100000000000000000 -> 001 -> 00000010  131072
* 00000000000001000000000000000000 -> 010 -> 00000100  262144
* 00000000000010000000000000000000 -> 011 -> 00001000  524288
* 00000000000100000000000000000000 -> 100 -> 00010000  1048576
* 00000000001000000000000000000000 -> 101 -> 00100000  2097152
* 00000000010000000000000000000000 -> 110 -> 01000000  4194304
* 00000000100000000000000000000000 -> 111 -> 10000000  8388608
* 00000001000000000000000000000000 -> 000 -> 00000001  16777216
* 00000010000000000000000000000000 -> 001 -> 00000010  33554432
* 00000100000000000000000000000000 -> 010 -> 00000100  67108864
* 00001000000000000000000000000000 -> 011 -> 00001000  134217728
* 00010000000000000000000000000000 -> 100 -> 00010000  268435456
* 00100000000000000000000000000000 -> 101 -> 00100000  536870912
* 01000000000000000000000000000000 -> 110 -> 01000000  1073741824
* 10000000000000000000000000000000 -> 111 -> 10000000  2147483648

komadori
komadori reviewed Aug 29, 2022
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crates/bevy_pbr/src/render/mesh.rs
let msaa_bits = ((msaa_samples - 1) & Self::MSAA_MASK_BITS) << Self::MSAA_SHIFT_BITS;
MeshPipelineKey::from_bits(msaa_bits).unwrap()
let msaa_bits =
(msaa_samples.trailing_zeros() & Self::MSAA_MASK_BITS) << Self::MSAA_SHIFT_BITS;
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Should this report an error in some way if the MSAA sample number is not a power of two?

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These checks are already inside the wgpu-rs.
Sample count must not only be the power of two, but also match the values chosen for the RenderTarget's attachments.

@Weibye Weibye added A-Rendering Drawing game state to the screen C-Code-Quality A section of code that is hard to understand or change labels Aug 29, 2022
cart
cart approved these changes Aug 30, 2022
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Looks good to me. Always glad to have more space in the pipeline keys!

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cart commented Aug 30, 2022

bors r+

bors bot pushed a commit that referenced this pull request Aug 30, 2022
@lain-dono
Use 3 bits of PipelineKey to store MSAA sample count (#5826)
24e5e10 
Sample count always power of two. Thus, it is enough to store `log2(sample_count)`.
This can be implemented using [u32::trailing_zeros](https://doc.rust-lang.org/stable/std/primitive.u32.html#method.trailing_zeros). Then we can restore sample count with the `1 << stored`.
You get 3 bits instead of 6 and up to 128x MSAA. This is more than is supported by any common hardware.

Full table of possible variations:

```
    original MSAA sample count      stored    loaded
* 00000000000000000000000000000000 -> 000 -> 00000001  1
  00000000000000000000000000000001 -> 000 -> 00000001  1
  00000000000000000000000000000010 -> 001 -> 00000010  2
  00000000000000000000000000000100 -> 010 -> 00000100  4
  00000000000000000000000000001000 -> 011 -> 00001000  8
  00000000000000000000000000010000 -> 100 -> 00010000  16
  00000000000000000000000000100000 -> 101 -> 00100000  32
  00000000000000000000000001000000 -> 110 -> 01000000  64
  00000000000000000000000010000000 -> 111 -> 10000000  128
* 00000000000000000000000100000000 -> 000 -> 00000001  256
* 00000000000000000000001000000000 -> 001 -> 00000010  512
* 00000000000000000000010000000000 -> 010 -> 00000100  1024
* 00000000000000000000100000000000 -> 011 -> 00001000  2048
* 00000000000000000001000000000000 -> 100 -> 00010000  4096
* 00000000000000000010000000000000 -> 101 -> 00100000  8192
* 00000000000000000100000000000000 -> 110 -> 01000000  16384
* 00000000000000001000000000000000 -> 111 -> 10000000  32768
* 00000000000000010000000000000000 -> 000 -> 00000001  65536
* 00000000000000100000000000000000 -> 001 -> 00000010  131072
* 00000000000001000000000000000000 -> 010 -> 00000100  262144
* 00000000000010000000000000000000 -> 011 -> 00001000  524288
* 00000000000100000000000000000000 -> 100 -> 00010000  1048576
* 00000000001000000000000000000000 -> 101 -> 00100000  2097152
* 00000000010000000000000000000000 -> 110 -> 01000000  4194304
* 00000000100000000000000000000000 -> 111 -> 10000000  8388608
* 00000001000000000000000000000000 -> 000 -> 00000001  16777216
* 00000010000000000000000000000000 -> 001 -> 00000010  33554432
* 00000100000000000000000000000000 -> 010 -> 00000100  67108864
* 00001000000000000000000000000000 -> 011 -> 00001000  134217728
* 00010000000000000000000000000000 -> 100 -> 00010000  268435456
* 00100000000000000000000000000000 -> 101 -> 00100000  536870912
* 01000000000000000000000000000000 -> 110 -> 01000000  1073741824
* 10000000000000000000000000000000 -> 111 -> 10000000  2147483648
```
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bors bot commented Aug 30, 2022

Pull request successfully merged into main.

Build succeeded:

@bors bors bot changed the title Use 3 bits of PipelineKey to store MSAA sample count [Merged by Bors] - Use 3 bits of PipelineKey to store MSAA sample count Aug 30, 2022
@bors bors bot closed this Aug 30, 2022
james7132 pushed a commit to james7132/bevy that referenced this pull request Oct 28, 2022
@lain-dono @james7132
Use 3 bits of PipelineKey to store MSAA sample count (bevyengine#5826)
701378f 
Sample count always power of two. Thus, it is enough to store `log2(sample_count)`.
This can be implemented using [u32::trailing_zeros](https://doc.rust-lang.org/stable/std/primitive.u32.html#method.trailing_zeros). Then we can restore sample count with the `1 << stored`.
You get 3 bits instead of 6 and up to 128x MSAA. This is more than is supported by any common hardware.

Full table of possible variations:

```
    original MSAA sample count      stored    loaded
* 00000000000000000000000000000000 -> 000 -> 00000001  1
  00000000000000000000000000000001 -> 000 -> 00000001  1
  00000000000000000000000000000010 -> 001 -> 00000010  2
  00000000000000000000000000000100 -> 010 -> 00000100  4
  00000000000000000000000000001000 -> 011 -> 00001000  8
  00000000000000000000000000010000 -> 100 -> 00010000  16
  00000000000000000000000000100000 -> 101 -> 00100000  32
  00000000000000000000000001000000 -> 110 -> 01000000  64
  00000000000000000000000010000000 -> 111 -> 10000000  128
* 00000000000000000000000100000000 -> 000 -> 00000001  256
* 00000000000000000000001000000000 -> 001 -> 00000010  512
* 00000000000000000000010000000000 -> 010 -> 00000100  1024
* 00000000000000000000100000000000 -> 011 -> 00001000  2048
* 00000000000000000001000000000000 -> 100 -> 00010000  4096
* 00000000000000000010000000000000 -> 101 -> 00100000  8192
* 00000000000000000100000000000000 -> 110 -> 01000000  16384
* 00000000000000001000000000000000 -> 111 -> 10000000  32768
* 00000000000000010000000000000000 -> 000 -> 00000001  65536
* 00000000000000100000000000000000 -> 001 -> 00000010  131072
* 00000000000001000000000000000000 -> 010 -> 00000100  262144
* 00000000000010000000000000000000 -> 011 -> 00001000  524288
* 00000000000100000000000000000000 -> 100 -> 00010000  1048576
* 00000000001000000000000000000000 -> 101 -> 00100000  2097152
* 00000000010000000000000000000000 -> 110 -> 01000000  4194304
* 00000000100000000000000000000000 -> 111 -> 10000000  8388608
* 00000001000000000000000000000000 -> 000 -> 00000001  16777216
* 00000010000000000000000000000000 -> 001 -> 00000010  33554432
* 00000100000000000000000000000000 -> 010 -> 00000100  67108864
* 00001000000000000000000000000000 -> 011 -> 00001000  134217728
* 00010000000000000000000000000000 -> 100 -> 00010000  268435456
* 00100000000000000000000000000000 -> 101 -> 00100000  536870912
* 01000000000000000000000000000000 -> 110 -> 01000000  1073741824
* 10000000000000000000000000000000 -> 111 -> 10000000  2147483648
```
ItsDoot pushed a commit to ItsDoot/bevy that referenced this pull request Feb 1, 2023
@lain-dono @ItsDoot
Use 3 bits of PipelineKey to store MSAA sample count (bevyengine#5826)
dbcb0d4 
Sample count always power of two. Thus, it is enough to store `log2(sample_count)`.
This can be implemented using [u32::trailing_zeros](https://doc.rust-lang.org/stable/std/primitive.u32.html#method.trailing_zeros). Then we can restore sample count with the `1 << stored`.
You get 3 bits instead of 6 and up to 128x MSAA. This is more than is supported by any common hardware.

Full table of possible variations:

```
    original MSAA sample count      stored    loaded
* 00000000000000000000000000000000 -> 000 -> 00000001  1
  00000000000000000000000000000001 -> 000 -> 00000001  1
  00000000000000000000000000000010 -> 001 -> 00000010  2
  00000000000000000000000000000100 -> 010 -> 00000100  4
  00000000000000000000000000001000 -> 011 -> 00001000  8
  00000000000000000000000000010000 -> 100 -> 00010000  16
  00000000000000000000000000100000 -> 101 -> 00100000  32
  00000000000000000000000001000000 -> 110 -> 01000000  64
  00000000000000000000000010000000 -> 111 -> 10000000  128
* 00000000000000000000000100000000 -> 000 -> 00000001  256
* 00000000000000000000001000000000 -> 001 -> 00000010  512
* 00000000000000000000010000000000 -> 010 -> 00000100  1024
* 00000000000000000000100000000000 -> 011 -> 00001000  2048
* 00000000000000000001000000000000 -> 100 -> 00010000  4096
* 00000000000000000010000000000000 -> 101 -> 00100000  8192
* 00000000000000000100000000000000 -> 110 -> 01000000  16384
* 00000000000000001000000000000000 -> 111 -> 10000000  32768
* 00000000000000010000000000000000 -> 000 -> 00000001  65536
* 00000000000000100000000000000000 -> 001 -> 00000010  131072
* 00000000000001000000000000000000 -> 010 -> 00000100  262144
* 00000000000010000000000000000000 -> 011 -> 00001000  524288
* 00000000000100000000000000000000 -> 100 -> 00010000  1048576
* 00000000001000000000000000000000 -> 101 -> 00100000  2097152
* 00000000010000000000000000000000 -> 110 -> 01000000  4194304
* 00000000100000000000000000000000 -> 111 -> 10000000  8388608
* 00000001000000000000000000000000 -> 000 -> 00000001  16777216
* 00000010000000000000000000000000 -> 001 -> 00000010  33554432
* 00000100000000000000000000000000 -> 010 -> 00000100  67108864
* 00001000000000000000000000000000 -> 011 -> 00001000  134217728
* 00010000000000000000000000000000 -> 100 -> 00010000  268435456
* 00100000000000000000000000000000 -> 101 -> 00100000  536870912
* 01000000000000000000000000000000 -> 110 -> 01000000  1073741824
* 10000000000000000000000000000000 -> 111 -> 10000000  2147483648
```
@lain-dono lain-dono mentioned this pull request Dec 18, 2023
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