EPISODE · Oct 31, 2025 · 28 MIN
Chromium Tile Raster Transform Propagation Audit
from Blink286 · host Free Debreuil
This detailed audit examines the complete code path within Chromium that determines the raster_transform_ property of a cc::Tile, which is an immutable scale and translation used during rasterization. The document clarifies that a Tile inherits this transform only once, during its construction, from its parent PictureLayerTiling. The tiling's transform, in turn, is set when the tiling is created by PictureLayerImpl, deriving its scale from content scale logic and an optional, usually fractional translation vector calculated only when necessary to align text to device pixels for clear rendering. The audit enumerates various scenarios that cause a tiling to be rebuilt with a new transform, such as scale changes or activation from a pending tree, ensuring that existing tiles remain transform-consistent until they are removed.
What this episode covers
This detailed audit examines the complete code path within Chromium that determines the raster_transform_ property of a cc::Tile, which is an immutable scale and translation used during rasterization. The document clarifies that a Tile inherits this transform only once, during its construction, from its parent PictureLayerTiling. The tiling's transform, in turn, is set when the tiling is created by PictureLayerImpl, deriving its scale from content scale logic and an optional, usually fractional translation vector calculated only when necessary to align text to device pixels for clear rendering. The audit enumerates various scenarios that cause a tiling to be rebuilt with a new transform, such as scale changes or activation from a pending tree, ensuring that existing tiles remain transform-consistent until they are removed.
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Chromium Tile Raster Transform Propagation Audit
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