Variable size scene encoding #152
Labels
architecture
Changes to the way it's put together
Comments
raphlinus
added a commit
that referenced
this issue
Mar 11, 2022
WIP - this passes the tests but rendering is still questionable. Closes #152
raphlinus
added a commit
that referenced
this issue
Mar 14, 2022
This patch switches to a variable size encoding of draw objects. In addition to the CPU-side scene encoding, it changes the representation of intermediate per draw object state from the `Annotated` struct to a variable "info" encoding. In addition, the bounding boxes are moved to a separate array (for a more "structure of "arrays" approach). Data that's unchanged from the scene encoding is not copied. Rather, downstream stages can access the data from the scene buffer (reducing allocation and copying). Prefix sums, computed in `DrawMonoid` track the offset of both scene and intermediate data. The tags for the CPU-side encoding have been split into their own stream (again a change from AoS to SoA style). This is not necessarily the final form. There's some stuff (including at least one piet-gpu-derive type) that can be deleted. In addition, the linewidth field should probably move from the info to path-specific. Also, the 1:1 correspondence between draw object and path has not yet been broken. Closes #152
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Right now, the main scene encoding is a sequence of fixed size draw objects. This has been the case for a while, but more recently path segments and a couple other things moved out of the scene encoding. In addition, there's a stream of
Annotatedobjects, also fixed size, with a 1:1 correspondence to theElementobjects in the scene encoding.It would be better for it to be fully variable size, I think. That would allow larger objects (gradients come to mind) without concern for bloating the encoding of other objects that may be more compact. Here's roughly what's involved.
The main step to unlock variable size encoding is to add two more prefix sums to the draw monoid: these count byte (or possibly u32) offsets within the element stream, and also a new variable size object to take the place of "annotated." Most of the functionality of Annotated moves to other places. The bounding box gets its own stream (this is generally a move towards SoA). anything currently just copied from Element is replaced by a read from the scene buffer (there's no value in copying it; this was originally seen as a simplification, so the memory read patterns were more uniform). The main thing that remains is the line equation for linear gradients (and a similar computation for radial gradients, when that's done).
There's nothing particularly deep about these changes. They follow the same general pattern as the element pipeline changes. Also there should be cleanup involved, the Rust-side encoding will I think no longer use piet-gpu-derive at all, and in general that could be removed.
The text was updated successfully, but these errors were encountered: