sprite_transform — GFX2D `sprite` op

• Data kinds: rgba → rgba

• Call: import gfx2d; gfx2d.sprite_transform(sprite, angle_deg=0.0, scale=1.0, interp='bilinear', out_shape=None) (or opsgfx2d.get("sprite_transform"))

Usage

Rotate and/or scale an `rgba` sprite about its centre.

A positive `angle_deg` turns the sprite clockwise on screen, because

the row axis points down. `interp is "nearest", "bilinear"` or

`"bicubic"` (a cubic spline; it overshoots, and the overshoot is clipped

back into the premultiplied range).

The resampling happens in premultiplied space and the result is

converted back. Interpolating straight colour instead mixes in the colour of

fully transparent pixels — usually black, and invisible in the alpha channel

— which shows up as a dark fringe. Measured on a white disc whose

transparent region is black, composited over mid-grey: the straight-space

result differs from this one by up to 0.203 and by 0.048 on average

over the pixels it changes (rotations of 13, 37 and 45 degrees; the maximum

was 0.197, 0.203, 0.156).

Exact where it can be: `angle_deg=0, scale=1` returns the input bit for

bit, and a multiple of 90 degrees with `interp="nearest"` permutes the

alpha channel exactly (colour matches to 1.2e-16, the cost of the

premultiply round trip). Everything else costs interpolation: the measured

round trip of `+37 then -37` degrees, bilinear, is a mean alpha error

of 0.0150 with a maximum of 0.8125 at the one pixel where the edge

crosses a sample.

`out_shape is (height, width)`; the default is the bounding box of the

transformed sprite, rounded up.

References (sample data, literature)

• Sample-data catalog (download URLs / licences) — 2-D uses skimage.data (BSD/public domain) plus synthetic images; 3-D lists download URLs for real data sources (Stanford, PDS, …).

• Operator provenance and references — the sources of the research/methods this op family came from.

• The canonical algorithm (author, year) and its uses are named in the family usage guide above.

Runnable examples (verified samples that actually call this op)

• gfx2d_scene — py -3.11 examples/gfx2d_scene.py

Ops the type connects to (they accept `rgba` as input)

premultiply · alpha_composite · sprite_blit · sprite_sheet_slice · nine_slice

Same category (`sprite`)

sprite_synthesize · sprite_blit · sprite_sheet_slice · nine_slice

*Provenance: gfx2d.py — GFX2D operator registry. This per-op note is generated by tools/opdocs.py md (do not hand-edit).*

sprite_transform — GFX2D sprite op