sprite_transform — GFX2D sprite op

• データ種: rgba → rgba

• 呼び出し: import gfx2d; gfx2d.sprite_transform(sprite, angle_deg=0.0, scale=1.0, interp='bilinear', out_shape=None) (または opsgfx2d.get("sprite_transform"))

使い方

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.

参考(サンプルデータ・文献)

• サンプルデータ カタログ(DL URL / ライセンス) — 2-D は skimage.data(BSD/public)+ 合成、3-D は実データ源(Stanford/PDS 等)の DL URL。

• 演算子の来歴・参考文献 — この op 族の元になった研究/手法の出典。

• アルゴリズムの正典(著者・年)と用途は上記ファミリ使い方ガイドに記載。

実行できる例(この op を実際に呼ぶ検証済みサンプル)

• gfx2d_scene — py -3.11 examples/gfx2d_scene.py

型が繋がる次の op(rgba を入力に取れる)

premultiply · alpha_composite · sprite_blit · sprite_sheet_slice · nine_slice

同カテゴリ(sprite)

sprite_synthesize · sprite_blit · sprite_sheet_slice · nine_slice

*Provenance: gfx2d.py — GFX2D operator registry. この per-op ノートは tools/opdocs.py md が自動生成(手編集しない)。*

© 2026 Kazufumi Furuse — Fullseye operator documentation. Licensed under Apache-2.0.