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9-patch metadata records the four border widths — top, right, bottom, left — of a stretchable UI sprite. The atlas packer does not alter how the sprite is packed; it only stores the border values in the data file. Your runtime reads those values to know which regions of the sprite can stretch and which must stay fixed.

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Usage

9-patch borders are set per sprite via the project file. There is no CLI flag.

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Project file configuration

Add a [[sprite_overrides]] entry for each sprite that needs 9-patch metadata: 
[[sprite_overrides]]
id         = "ui/button"
nine_patch = { top = 8, right = 8, bottom = 8, left = 8 }

[[sprite_overrides]]
id         = "ui/panel"
nine_patch = { top = 12, right = 20, bottom = 12, left = 20 }
Border values are in source pixels before any scale variant is applied. When a scale variant is used, FastPack scales the border values proportionally in that variant’s data file.

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Example output

A ui/button sprite with nine_patch = { top=8, right=8, bottom=8, left=8 }: JSON Hash output: 
"ui/button": {
  "frame": { "x": 2, "y": 2, "w": 64, "h": 32 },
  "rotated": false,
  "trimmed": false,
  "spriteSourceSize": { "x": 0, "y": 0, "w": 64, "h": 32 },
  "sourceSize": { "w": 64, "h": 32 },
  "ninePatch": { "top": 8, "right": 8, "bottom": 8, "left": 8 }
}
The ninePatch field is omitted for sprites that have no override.

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Technical details

ninePatch is written in camelCase in the JSON output, consistent with the other camelCase fields (spriteSourceSize, sourceSize).
Border values in the data file are in the variant’s pixel space. A @0.5x scale variant writes borders that are half the project-file values.

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TexturePacker compatibility

TexturePacker stores 9-patch borders in a slices array. FastPack uses a flat ninePatch object, which is more compact and widely used in game engines. If your engine expects the slices format, a small post-processing step is needed to remap the field.

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