We want to only rasterize blobs during scene building. This would simplify a whole lot of error-prone code and ensure we never do blob rasterization on the render backend.

To do this we have to ensure that blob blob visible areas are not too big.

SVG uses:
const nsRect& untransformedPaintRect =
aWrappingItem->GetUntransformedPaintRect();

Fallback uses:
auto visibleRect = LayerIntRect::FromUnknownRect(
ScaleToOutsidePixelsOffset(
aItem->GetBuildingRect(), scale.width,
scale.height, appUnitsPerDevPixel, residualOffset))
.Intersect(dtRect);

Both of those should have reasonable bounds. Any situation where this isn't true can be considered a bug so I think we can proceed here.

If this change lands without making waves, a lot of complicated blob infrastructure will be removed as a followup.

Depends on D49185

When blobs were lazily rasterized it was relatively cheap to create very large blob layers. Now that we move to pre-rasetrizing all blob tiles during scene building, large blob layers cause excessive memory allocation and CPU usage.

https://hg.mozilla.org/mozilla-central/rev/99c2a028927d
https://hg.mozilla.org/mozilla-central/rev/218965aab2d5
https://hg.mozilla.org/mozilla-central/rev/f32d7f9eb04f

I haven't landed the late blob rasterization removal yet. Before this can happen we need to cache the rasterized content (we currently throw it away after upload), otherwise we get missing tiles after device resets and memory pressure events which we currently rasterize using the late blob rasterization path.

(In reply to Nicolas Silva [:nical] from comment #8)

I haven't landed the late blob rasterization removal yet. Before this can happen we need to cache the rasterized content (we currently throw it away after upload), otherwise we get missing tiles after device resets and memory pressure events which we currently rasterize using the late blob rasterization path.

Can we continue to throw it away and rely on needing a new scene when a device reset/memory pressure happens?

Probably yes, I'll try that.

https://hg.mozilla.org/mozilla-central/rev/aff8eef07d07