A rendering engine library for Go supporting both SDL2 and WebAssembly (HTML Canvas) targets.
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package render
import (
"math"
)
// IterLine is a generator that returns the X,Y coordinates to draw a line.
// https://en.wikipedia.org/wiki/Digital_differential_analyzer_(graphics_algorithm)
func IterLine(p1 Point, p2 Point) chan Point {
var (
x1 = p1.X
y1 = p1.Y
x2 = p2.X
y2 = p2.Y
)
generator := make(chan Point)
go func() {
var (
dx = float64(x2 - x1)
dy = float64(y2 - y1)
)
var step float64
if math.Abs(dx) >= math.Abs(dy) {
step = math.Abs(dx)
} else {
step = math.Abs(dy)
}
dx = dx / step
dy = dy / step
x := float64(x1)
y := float64(y1)
for i := 0; i <= int(step); i++ {
generator <- NewPoint(int(x), int(y))
x += dx
y += dy
}
close(generator)
}()
return generator
}
// IterRect loops through all the points forming a rectangle between the
// top-left point and the bottom-right point.
func IterRect(p1, p2 Point) chan Point {
generator := make(chan Point)
go func() {
var (
TopLeft = p1
BottomRight = p2
TopRight = Point{
X: BottomRight.X,
Y: TopLeft.Y,
}
BottomLeft = Point{
X: TopLeft.X,
Y: BottomRight.Y,
}
dedupe = map[Point]interface{}{}
)
// Trace all four edges and yield it.
var edges = []struct {
A Point
B Point
}{
{TopLeft, TopRight},
{TopLeft, BottomLeft},
{BottomLeft, BottomRight},
{TopRight, BottomRight},
}
for _, edge := range edges {
for pt := range IterLine(edge.A, edge.B) {
if _, ok := dedupe[pt]; !ok {
generator <- pt
dedupe[pt] = nil
}
}
}
close(generator)
}()
return generator
}
// IterEllipse iterates an Ellipse using two Points as the top-left and
// bottom-right corners of a rectangle that encompasses the ellipse.
func IterEllipse(A, B Point) chan Point {
var (
width = AbsInt(B.X - A.X)
height = AbsInt(B.Y - A.Y)
radius = NewPoint(width/2, height/2)
center = NewPoint(AbsInt(B.X-radius.X), AbsInt(B.Y-radius.Y))
)
return MidpointEllipse(center, radius)
}