1 files changed, 98 insertions, 0 deletions
diff --git a/src/view/com/lightbox/ImageViewing/transforms.ts b/src/view/com/lightbox/ImageViewing/transforms.ts
new file mode 100644
index 000000000..05476678f
--- /dev/null
+++ b/src/view/com/lightbox/ImageViewing/transforms.ts
@@ -0,0 +1,98 @@
+import type {Position} from './@types'
+
+export type TransformMatrix = [
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+  number,
+]
+
+// These are affine transforms. See explanation of every cell here:
+// https://en.wikipedia.org/wiki/Transformation_matrix#/media/File:2D_affine_transformation_matrix.svg
+
+export function createTransform(): TransformMatrix {
+  'worklet'
+  return [1, 0, 0, 0, 1, 0, 0, 0, 1]
+}
+
+export function applyRounding(t: TransformMatrix) {
+  'worklet'
+  t[2] = Math.round(t[2])
+  t[5] = Math.round(t[5])
+  // For example: 0.985, 0.99, 0.995, then 1:
+  t[0] = Math.round(t[0] * 200) / 200
+  t[4] = Math.round(t[0] * 200) / 200
+}
+
+// We're using a limited subset (always scaling and translating while keeping aspect ratio) so
+// we can assume the transform doesn't encode have skew, rotation, or non-uniform stretching.
+
+// All write operations are applied in-place to avoid unnecessary allocations.
+
+export function readTransform(t: TransformMatrix): [number, number, number] {
+  'worklet'
+  const scale = t[0]
+  const translateX = t[2]
+  const translateY = t[5]
+  return [translateX, translateY, scale]
+}
+
+export function prependTranslate(t: TransformMatrix, x: number, y: number) {
+  'worklet'
+  t[2] += t[0] * x + t[1] * y
+  t[5] += t[3] * x + t[4] * y
+}
+
+export function prependScale(t: TransformMatrix, value: number) {
+  'worklet'
+  t[0] *= value
+  t[1] *= value
+  t[3] *= value
+  t[4] *= value
+}
+
+export function prependTransform(ta: TransformMatrix, tb: TransformMatrix) {
+  'worklet'
+  // In-place matrix multiplication.
+  const a00 = ta[0],
+    a01 = ta[1],
+    a02 = ta[2]
+  const a10 = ta[3],
+    a11 = ta[4],
+    a12 = ta[5]
+  const a20 = ta[6],
+    a21 = ta[7],
+    a22 = ta[8]
+  ta[0] = a00 * tb[0] + a01 * tb[3] + a02 * tb[6]
+  ta[1] = a00 * tb[1] + a01 * tb[4] + a02 * tb[7]
+  ta[2] = a00 * tb[2] + a01 * tb[5] + a02 * tb[8]
+  ta[3] = a10 * tb[0] + a11 * tb[3] + a12 * tb[6]
+  ta[4] = a10 * tb[1] + a11 * tb[4] + a12 * tb[7]
+  ta[5] = a10 * tb[2] + a11 * tb[5] + a12 * tb[8]
+  ta[6] = a20 * tb[0] + a21 * tb[3] + a22 * tb[6]
+  ta[7] = a20 * tb[1] + a21 * tb[4] + a22 * tb[7]
+  ta[8] = a20 * tb[2] + a21 * tb[5] + a22 * tb[8]
+}
+
+export function prependPan(t: TransformMatrix, translation: Position) {
+  'worklet'
+  prependTranslate(t, translation.x, translation.y)
+}
+
+export function prependPinch(
+  t: TransformMatrix,
+  scale: number,
+  origin: Position,
+  translation: Position,
+) {
+  'worklet'
+  prependTranslate(t, translation.x, translation.y)
+  prependTranslate(t, origin.x, origin.y)
+  prependScale(t, scale)
+  prependTranslate(t, -origin.x, -origin.y)
+}