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shadows.go
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/
shadows.go
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package canvas
import (
"image"
"math"
"github.com/tfriedel6/canvas/backend/backendbase"
)
func (cv *Canvas) drawShadow(pts [][2]float64, mask *image.Alpha, canOverlap bool) {
if cv.state.shadowColor.A == 0 {
return
}
if cv.state.shadowOffsetX == 0 && cv.state.shadowOffsetY == 0 {
return
}
if cv.shadowBuf == nil || cap(cv.shadowBuf) < len(pts) {
cv.shadowBuf = make([][2]float64, 0, len(pts)+1000)
}
cv.shadowBuf = cv.shadowBuf[:0]
for _, pt := range pts {
cv.shadowBuf = append(cv.shadowBuf, [2]float64{
pt[0] + cv.state.shadowOffsetX,
pt[1] + cv.state.shadowOffsetY,
})
}
color := cv.state.shadowColor
color.A = uint8(math.Round(((float64(color.A) / 255.0) * cv.state.globalAlpha) * 255.0))
style := backendbase.FillStyle{Color: color, Blur: cv.state.shadowBlur}
if mask != nil {
if len(cv.shadowBuf) != 4 {
panic("invalid number of points to fill with mask, must be 4")
}
var quad [4][2]float64
copy(quad[:], cv.shadowBuf)
cv.b.FillImageMask(&style, mask, quad)
} else {
cv.b.Fill(&style, cv.shadowBuf, canOverlap)
}
}