Struct Quad 

pub struct Quad {
    pub corners: [Point; 4],
}

Four corners, in order: top-left, top-right, bottom-right, bottom-left.

The order is the contract. It matches the unit square’s (0,0), (1,0), (1,1), (0,1), which is how a texture is indexed, so “top-left” means the corner the picture’s top-left goes to — whatever that does to the geometry on screen.

Fields

corners: [Point; 4]

The corners, clockwise from the picture’s top-left.

Implementations

impl Quad

pub const fn new(corners: [Point; 4]) -> Self

A quad from four corners, in the documented order.

pub fn from_rect(rect: Rect) -> Self

The rectangle as a quad — the case with no keystone at all.

pub fn keystone(rect: Rect, inset: f64) -> Self

A symmetric keystone: the top edge narrowed by inset at each end.

The shape a projector makes when it is aimed upwards, and the one most people want when they reach for “trapezoid”.

pub fn signed_area(self) -> f64

Twice the signed area, by the shoelace formula. Positive is clockwise in a y-down coordinate system.

pub fn is_convex(self) -> bool

Whether the quad is convex and non-degenerate.

A concave or self-intersecting quad has no single projective map onto it, so this is not a style preference — it is the precondition for homography meaning anything.

pub fn bounds(self) -> Rect

The axis-aligned box around the quad.

pub fn contains(self, point: Point) -> bool

Whether a point is inside the quad.

pub fn homography(self) -> Result<Mat3>

The projective map from the unit square onto this quad.

(0,0) lands on the first corner, (1,0) on the second, and so on, so feeding it texture coordinates maps the picture into the quad. The bottom row is the perspective part: it is zero exactly when the quad is a parallelogram, which is the only case where linear interpolation would have been right.

This is Heckbert’s unit-square-to-quadrilateral construction; it is closed-form, so there is no solve and no iteration.

Errors

Error::Placement if the quad is concave, self-intersecting, or has three corners in a line.

pub fn inverse_homography(self) -> Result<Mat3>

The map the other way: from this quad back to the unit square.

This is what a fragment shader uses. It starts at a screen pixel and has to find the texel, which is the inverse direction from the one that is natural to write down.

Errors

As homography.

pub fn is_affine(self) -> bool

Whether this quad needs the perspective divide at all.

A parallelogram does not: its map is affine, linear interpolation is exact, and a renderer may take a cheaper path.

Trait Implementations

impl Clone for Quad

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for Quad

impl Debug for Quad

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl PartialEq for Quad

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for Quad