Vello CPU: Add public API to render with offset/stride#1597
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Signed-off-by: Nico Burns <nico@nicoburns.com>
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nicoburns
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Apr 25, 2026
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| let mut regions = | ||
| Regions::new(bbox_width, bbox_height, pixmap.data_as_u8_slice_mut()); |
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I did not update this instance of Regions::new, as I think it's rendering into an intermediate layer and not the output buffer. Does that seems correct?
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I think I might have a better idea now how to implement this and consolidate it with exsting APIs. Need to try it out, but if it works out I will open a PR soon. |
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Supersedes linebender#1597, closes linebender#1382. # Motivation Right now, we have two rendering APIs: `render_to_pixmap` and `composite_to_pixmap_at_offset`. We are about to add a third one in linebender#1597. Having this many APIs is very confusing, and after thinking about this more closely I realized that really, what we have been doing is adding methods that do similar things but just with different knobs enabled/disabled. I think it would be much cleaner if we had _one single_ API entry point for rendering to a pixmap, and instead expose the available knobs as a simple settings struct. # Implementation Therefore, this PR proposes to: 1) Expose **one single** `render` method that can be used to render the contents of a `RenderContext` into `Pixmap`-like struct. 2) Introduce a `PixmapMut` struct to allow constructing a render target from a mutable borrowed byte slice. Let `render` always take a ` PixmapMut`, allowing to pass both, a custom buffer or an owned pixmap as the render target. 3) Introduce a `CompositeMode` enum that defines whether the contents of a pixmap should be completely replaced (by default), or whether source-over compositing should be used. 4) Also introduce a `PixelFormat` struct, to possibly allow `Bgra8` in the future, which is useful for MacOS. 5) `RenderMode` has been moved from being stored in `RenderContext` to instead being a setting during rasterization. I initially stored this in `RenderContext` because I thought it might happen that the setting will also be needed during scene construction, but this turned out to not be the case in the end. 5) Previously, the implicit assumption was that `RenderContext` and `Pixmap` always need to have the same size, although it "accidentally" was possible for them to _not_ have the same size, and some people have made use of that. This PR relaxes the conditions imposed on the size, explicitly allowing size mismatches and also documents what the intended semantics are for each. # Testing I've added some new tests for the expected behavior. Existing tests pass. I've also ran `vello_cpu_winit` with the different scenes and didn't notice any regressions. **TODO: I still want to run this version against my PDF test suite, but this shouldn't block a review.**
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PixmapMut<'_>and stride invello_cpu? #1382This PR is pretty simple as the logic for doing this already existed (I think added for
RenderContext::composite_to_pixmap_at_offset, and this just plumbing through 4 extrau16parameters in a bunch of places.Todo
The logic in this PR is unfortunately not quite right as things stand. Testing shows the stride not being accounted for even when using the new method)(looks like I'd just missed a method that needed to be updated)