# PerspectiveTransform.fromTransformedSquare constructor

PerspectiveTransform.fromTransformedSquare(
1. List<> vertices
)

Creates a PerspectiveTransform that transforms a 1x1 square into the given quadrilateral, expressed as a list of its vertices.

## Implementation

``````factory PerspectiveTransform.fromTransformedSquare(
List<Position> vertices,
) {
assert(vertices.length == 4);
final p1 = vertices[0].toDouble(),
p2 = vertices[1].toDouble(),
p3 = vertices[2].toDouble(),
p4 = vertices[3].toDouble();

final dx3 = p1.x - p2.x + p3.x - p4.x;
final dy3 = p1.y - p2.y + p3.y - p4.y;
if (dx3 == 0 && dy3 == 0) {
// Affine
return PerspectiveTransform([
p2.x - p1.x, p2.y - p1.y, 0, //
p3.x - p2.x, p3.y - p2.y, 0, //
p1.x, p1.y, 1, //
]);
} else {
final dx1 = p2.x - p3.x;
final dx2 = p4.x - p3.x;
final dy1 = p2.y - p3.y;
final dy2 = p4.y - p3.y;
final denominator = dx1 * dy2 - dx2 * dy1;
final a13 = (dx3 * dy2 - dx2 * dy3) / denominator;
final a23 = (dx1 * dy3 - dx3 * dy1) / denominator;
return PerspectiveTransform([
p2.x - p1.x + a13 * p2.x, p2.y - p1.y + a13 * p2.y, a13, //
p4.x - p1.x + a23 * p4.x, p4.y - p1.y + a23 * p4.y, a23, //
p1.x, p1.y, 1 //
]);
}
}``````