301 lines
8.4 KiB
Go
301 lines
8.4 KiB
Go
package pixel
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import (
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"fmt"
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"math"
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"math/cmplx"
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"github.com/go-gl/mathgl/mgl64"
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)
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// Vec is a 2D vector type. It is unusually implemented as complex128 for convenience. Since
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// Go does not allow operator overloading, implementing vector as a struct leads to a bunch of
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// methods for addition, subtraction and multiplication of vectors. With complex128, much of
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// this functionality is given through operators.
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//
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// Create vectors with the V constructor:
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//
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// u := pixel.V(1, 2)
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// v := pixel.V(8, -3)
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//
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// Add and subtract them using the standard + and - operators:
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//
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// w := u + v
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// fmt.Println(w) // Vec(9, -1)
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// fmt.Println(u - v) // Vec(-7, 5)
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//
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// Additional standard vector operations can be obtained with methods:
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//
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// u := pixel.V(2, 3)
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// v := pixel.V(8, 1)
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// if u.X() < 0 {
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// fmt.Println("this won't happen")
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// }
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// x := u.Unit().Dot(v.Unit())
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type Vec complex128
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// V returns a new 2D vector with the given coordinates.
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func V(x, y float64) Vec {
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return Vec(complex(x, y))
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}
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// X returns a 2D vector with coordinates (x, 0).
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func X(x float64) Vec {
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return V(x, 0)
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}
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// Y returns a 2D vector with coordinates (0, y).
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func Y(y float64) Vec {
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return V(0, y)
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}
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// String returns the string representation of the vector u.
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//
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// u := pixel.V(4.5, -1.3)
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// u.String() // returns "Vec(4.5, -1.3)"
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// fmt.Println(u) // Vec(4.5, -1.3)
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func (u Vec) String() string {
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return fmt.Sprintf("Vec(%v, %v)", u.X(), u.Y())
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}
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// X returns the x coordinate of the vector u.
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func (u Vec) X() float64 {
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return real(u)
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}
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// Y returns the y coordinate of the vector u.
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func (u Vec) Y() float64 {
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return imag(u)
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}
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// XY returns the components of the vector in two return values.
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func (u Vec) XY() (x, y float64) {
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return real(u), imag(u)
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}
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// Len returns the length of the vector u.
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func (u Vec) Len() float64 {
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return cmplx.Abs(complex128(u))
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}
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// Angle returns the angle between the vector u and the x-axis. The result is in the range [-Pi, Pi].
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func (u Vec) Angle() float64 {
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return cmplx.Phase(complex128(u))
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}
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// Unit returns a vector of length 1 with the same angle as u.
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func (u Vec) Unit() Vec {
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return u / V(u.Len(), 0)
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}
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// Scaled returns the vector u multiplied by c.
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func (u Vec) Scaled(c float64) Vec {
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return u * V(c, 0)
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}
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// ScaledXY returns the vector u multiplied by vector v component-wise.
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func (u Vec) ScaledXY(v Vec) Vec {
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return V(u.X()*v.X(), u.Y()*v.Y())
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}
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// Rotated returns the vector u rotated by the given angle in radians.
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func (u Vec) Rotated(angle float64) Vec {
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sin, cos := math.Sincos(angle)
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return u * V(cos, sin)
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}
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// Dot returns the dot product of vectors u and v.
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func (u Vec) Dot(v Vec) float64 {
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return u.X()*v.X() + u.Y()*v.Y()
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}
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// Cross return the cross product of vectors u and v.
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func (u Vec) Cross(v Vec) float64 {
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return u.X()*v.Y() - v.X()*u.Y()
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}
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// Map applies the function f to both x and y components of the vector u and returns the modified
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// vector.
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func (u Vec) Map(f func(float64) float64) Vec {
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return V(
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f(u.X()),
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f(u.Y()),
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)
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}
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// Lerp returns a linear interpolation between vectors a and b.
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//
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// This function basically returns a point along the line between a and b and t chooses which point.
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// If t is 0, then a will be returned, if t is 1, b will be returned. Anything between 0 and 1 will
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// return the appropriate point between a and b and so on.
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func Lerp(a, b Vec, t float64) Vec {
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return a.Scaled(1-t) + b.Scaled(t)
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}
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// Rect is a 2D rectangle aligned with the axes of the coordinate system. It is defined by two
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// points, Min and Max.
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//
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// The invariant should hold, that Max's components are greater or equal than Min's components
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// respectively.
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type Rect struct {
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Min, Max Vec
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}
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// R returns a new Rect with given the Min and Max coordinates.
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func R(minX, minY, maxX, maxY float64) Rect {
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return Rect{
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Min: V(minX, minY),
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Max: V(maxX, maxY),
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}.Norm()
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}
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// Norm returns the Rect in normal form, such that Max is component-wise greater or equal than Min.
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func (r Rect) Norm() Rect {
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return Rect{
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Min: V(
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math.Min(r.Min.X(), r.Max.X()),
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math.Min(r.Min.Y(), r.Max.Y()),
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),
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Max: V(
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math.Max(r.Min.X(), r.Max.X()),
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math.Max(r.Min.Y(), r.Max.Y()),
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),
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}
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}
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// String returns the string representation of the rectangle.
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//
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// r := pixel.R(100, 50, 200, 300)
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// r.String() // returns "Rect(100, 50, 200, 300)"
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// fmt.Println(r) // Rect(100, 50, 200, 300)
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func (r Rect) String() string {
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return fmt.Sprintf("Rect(%v, %v, %v, %v)", r.Min.X(), r.Min.Y(), r.Max.X(), r.Max.Y())
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}
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// W returns the width of the rectangle.
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func (r Rect) W() float64 {
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return r.Max.X() - r.Min.X()
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}
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// H returns the height of the rectangle.
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func (r Rect) H() float64 {
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return r.Max.Y() - r.Min.Y()
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}
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// Size returns the vector of width and height as components respectively.
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func (r Rect) Size() Vec {
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return V(r.W(), r.H())
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}
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// Center returns the position of the center of the rectangle.
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func (r Rect) Center() Vec {
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return (r.Min + r.Max) / 2
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}
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// Moved returns the Rect moved (both Min and Max) by the given vector delta.
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func (r Rect) Moved(delta Vec) Rect {
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return Rect{
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Min: r.Min + delta,
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Max: r.Max + delta,
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}
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}
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// Resized returns the Rect resized to the given size while keeping the position of the given anchor.
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//
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// r.Resized(r.Min, size) // resizes while keeping the position of the lower-left corner
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// r.Resized(r.Max, size) // same with the top-right corner
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// r.Resized(r.Center(), size) // resizes around the center
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//
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// This function does not make sense for size of zero area and will panic. Use ResizeMin in the case
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// of zero area.
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func (r Rect) Resized(anchor, size Vec) Rect {
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if r.W()*r.H() == 0 || size.X()*size.Y() == 0 {
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panic(fmt.Errorf("(%T).Resize: zero area", r))
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}
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fraction := size.ScaledXY(V(1/r.W(), 1/r.H()))
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return Rect{
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Min: anchor + (r.Min - anchor).ScaledXY(fraction),
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Max: anchor + (r.Max - anchor).ScaledXY(fraction),
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}
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}
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// ResizedMin returns the Rect resized to the given size while keeping the position of the Rect's
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// Min.
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//
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// Sizes of zero area are safe here.
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func (r Rect) ResizedMin(size Vec) Rect {
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return Rect{
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Min: r.Min,
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Max: r.Min + size,
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}
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}
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// Contains checks whether a vector u is contained within this Rect (including it's borders).
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func (r Rect) Contains(u Vec) bool {
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return r.Min.X() <= u.X() && u.X() <= r.Max.X() && r.Min.Y() <= u.Y() && u.Y() <= r.Max.Y()
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}
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// Matrix is a 3x3 transformation matrix that can be used for all kinds of spacial transforms, such
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// as movement, scaling and rotations.
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//
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// Matrix has a handful of useful methods, each of which adds a transformation to the matrix. For
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// example:
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//
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// pixel.IM.Moved(pixel.V(100, 200)).Rotated(0, math.Pi/2)
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//
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// This code creates a Matrix that first moves everything by 100 units horizontaly and 200 units
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// vertically and then rotates everything by 90 degrees around the origin.
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type Matrix [9]float64
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// IM stands for identity matrix. Does nothing, no transformation.
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var IM = Matrix(mgl64.Ident3())
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// Moved moves everything by the delta vector.
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func (m Matrix) Moved(delta Vec) Matrix {
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m3 := mgl64.Mat3(m)
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m3 = mgl64.Translate2D(delta.XY()).Mul3(m3)
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return Matrix(m3)
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}
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// ScaledXY scales everything around a given point by the scale factor in each axis respectively.
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func (m Matrix) ScaledXY(around Vec, scale Vec) Matrix {
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m3 := mgl64.Mat3(m)
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m3 = mgl64.Translate2D((-around).XY()).Mul3(m3)
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m3 = mgl64.Scale2D(scale.XY()).Mul3(m3)
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m3 = mgl64.Translate2D(around.XY()).Mul3(m3)
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return Matrix(m3)
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}
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// Scaled scales everything around a given point by the scale factor.
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func (m Matrix) Scaled(around Vec, scale float64) Matrix {
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return m.ScaledXY(around, V(scale, scale))
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}
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// Rotated rotates everything around a given point by the given angle in radians.
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func (m Matrix) Rotated(around Vec, angle float64) Matrix {
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m3 := mgl64.Mat3(m)
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m3 = mgl64.Translate2D((-around).XY()).Mul3(m3)
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m3 = mgl64.Rotate3DZ(angle).Mul3(m3)
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m3 = mgl64.Translate2D(around.XY()).Mul3(m3)
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return Matrix(m3)
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}
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// Project applies all transformations added to the Matrix to a vector u and returns the result.
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//
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// Time complexity is O(1).
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func (m Matrix) Project(u Vec) Vec {
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m3 := mgl64.Mat3(m)
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proj := m3.Mul3x1(mgl64.Vec3{u.X(), u.Y(), 1})
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return V(proj.X(), proj.Y())
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}
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// Unproject does the inverse operation to Project.
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//
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// Time complexity is O(1).
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func (m Matrix) Unproject(u Vec) Vec {
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m3 := mgl64.Mat3(m)
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inv := m3.Inv()
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unproj := inv.Mul3x1(mgl64.Vec3{u.X(), u.Y(), 1})
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return V(unproj.X(), unproj.Y())
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}
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