Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

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

Closed
wants to merge 2 commits into from

Conversation

lain-dono
Copy link
Contributor

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

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;
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Should this report an error in some way if the MSAA sample number is not a power of two?

Copy link
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

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
Copy link
Member

@cart cart left a comment

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Looks good to me. Always glad to have more space in the pipeline keys!

@cart
Copy link
Member

cart commented Aug 30, 2022

bors r+

bors bot pushed a commit that referenced this pull request Aug 30, 2022
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
```
@bors
Copy link
Contributor

bors bot commented Aug 30, 2022

@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
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
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
```
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Labels
A-Rendering Drawing game state to the screen C-Code-Quality A section of code that is hard to understand or change
Projects
None yet
Development

Successfully merging this pull request may close these issues.

4 participants