Change Details

This patch moves `Mesh` polygon material indices out of the `MPoly` struct to a generic attribute, with the goal of simplifying code, and eventually reducing memory usage and improving performance. Until 4.0, meshes are written to and read with the existing format, and backwards compatibility in DNA means we can't actually remove the field from the struct yet, but there may be ways around that in the future. Ref T95967 TODO: - Fix multires material evaluation: `ccgDM_copyFinalPolyArray` - Run tests, fix as needed Branch: `refactor-mesh-material-index-generic`

This patch moves material indices from the mesh `MPoly` struct to a generic integer attribute. The builtin material index was already exposed in geometry nodes, but this makes it a "proper" attribute accessible with Python and visible in the "Attributes" panel. The goals of the refactor are code simplification and memory and performance improvements, mainly because the attribute doesn't have to be stored and processed if there are no materials. However, until 4.0, material indices will still be read and written in the old format, meaning there may be a temporary increase in memory usage. Further notes: * Completely removing the `MPoly.mat_nr` after 4.0 may require changes to DNA or introducing a new `MPoly` type. * Access to material indices from the RNA `MeshPolygon` type is slower with this patch. The `material_index` attribute can be used instead. * Cycles is changed to read from the attribute instead. * BMesh isn't changed in this patch. Theoretically it could be though, to save 2 bytes per face when no materials are used. * Eventually we could use a 16 bit integer attribute type instead. Ref T95967 Branch: `refactor-mesh-material-index-generic`

This patch moves `Mesh` polygon material indices out of thefrom the mesh `MPoly` struct to a a generic attribute, with the goal of simplifying code,integer attribute. and eventually reducingThe builtin material index was already memory usageexposed in geometry nodes, but this makes it a "proper" attribute accessible with Python and improving performancevisible in the "Attributes" panel. Until 4.0, meshes are written to and read with the existing format,The goals of the refactor are code simplification and backwardsmemory and compatibility in DNA means we can't actually removperformance improvements, mainly because the field from the struct yet,attribute doesn't have but there may be ways around that in the future. Ref T95967to be stored and processed if there are no materials. However, until 4.0, material indices will still be read and written in the old format, meaning there may be a temporary increase in memory usage. TODO:Further notes: * Completely removing the `MPoly.mat_nr` after 4.0 may require changes to DNA or introducing a new `MPoly` type. - Fix multires* Access to material evaluation: `ccgDM_copyFinalPolyArray`indices from the RNA `MeshPolygon` type is slower - Run tests, with this patch. The `material_index` attribute can be used instead. * Cycles is changed to read from the attribute instead. * BMesh isn't changed in this patch. fix as neededTheoretically it could be though, to save 2 bytes per face when no materials are used. * Eventually we could use a 16 bit integer attribute type instead. Ref T95967 Branch: `refactor-mesh-material-index-generic`