backend/x/canvas/line.go

96 lines
1.6 KiB
Go

package xcanvas
import "image"
import "github.com/jezek/xgbutil/xgraphics"
// TODO: clip the line to the bounds
func (this *pen) line (
c xgraphics.BGRA,
min image.Point,
max image.Point,
) {
context := linePlottingContext {
plottingContext: plottingContext {
image: this.image,
color: c,
weight: this.weight,
},
min: min,
max: max,
}
if abs(max.Y - min.Y) < abs(max.X - min.X) {
if max.X < min.X { context.swap() }
context.lineLow()
} else {
if max.Y < min.Y { context.swap() }
context.lineHigh()
}
}
type linePlottingContext struct {
plottingContext
min image.Point
max image.Point
}
func (context *linePlottingContext) swap () {
temp := context.max
context.max = context.min
context.min = temp
}
func (context linePlottingContext) lineLow () {
deltaX := context.max.X - context.min.X
deltaY := context.max.Y - context.min.Y
yi := 1
if deltaY < 0 {
yi = -1
deltaY *= -1
}
D := (2 * deltaY) - deltaX
point := context.min
for ; point.X < context.max.X; point.X ++ {
context.plot(point)
if D > 0 {
D += 2 * (deltaY - deltaX)
point.Y += yi
} else {
D += 2 * deltaY
}
}
}
func (context linePlottingContext) lineHigh () {
deltaX := context.max.X - context.min.X
deltaY := context.max.Y - context.min.Y
xi := 1
if deltaX < 0 {
xi = -1
deltaX *= -1
}
D := (2 * deltaX) - deltaY
point := context.min
for ; point.Y < context.max.Y; point.Y ++ {
context.plot(point)
if D > 0 {
point.X += xi
D += 2 * (deltaX - deltaY)
} else {
D += 2 * deltaX
}
}
}
func abs (n int) int {
if n < 0 { n *= -1}
return n
}