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swipes.go
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/
swipes.go
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package main
import (
"image/color"
"github.com/faiface/pixel"
"github.com/faiface/pixel/imdraw"
)
const (
fadeRate float64 = 255 * 8
moveRate float64 = 16 * 2
)
var (
Swipes []*swipe
swipeIMD = imdraw.New(nil)
)
type swipe struct {
pos pixel.Vec
dir pixel.Vec
size float64
c color.RGBA
}
func NewSwipe(pos, dir pixel.Vec, size float64, c color.RGBA) {
s := swipe{
pos: pos,
dir: dir.Unit(),
size: size,
c: c,
}
Swipes = append(Swipes, &s)
}
func updateSwipes(dt float64) {
for i, s := range Swipes {
if s.update(dt) {
copy(Swipes[i:], Swipes[i+1:])
Swipes[len(Swipes)-1] = nil
Swipes = Swipes[:len(Swipes)-1]
}
}
}
func drawSwipes(target pixel.Target) {
swipeIMD.Clear()
for _, s := range Swipes {
s.draw(swipeIMD)
}
swipeIMD.Draw(target)
}
func (s *swipe) update(dt float64) bool {
if s == nil {
return false
}
nextFade := uint8(dt * fadeRate)
if s.c.A <= nextFade {
return true
}
if s.c.R < nextFade {
s.c.R = 0x00
}
if s.c.G < nextFade {
s.c.G = 0x00
}
if s.c.B < nextFade {
s.c.B = 0x00
}
s.c.A -= nextFade
s.pos = s.pos.Add(s.dir.Scaled(dt * moveRate))
return false
}
func (s *swipe) draw(imd *imdraw.IMDraw) {
if s == nil {
return
}
imd.Color = s.c
imd.Push(s.pos)
imd.Circle(s.size, 0)
}