blend.go

/*Package blend provides common image blending modes.*/
package blend

import (
	"image"
	"math"

	"github.com/anthonynsimon/bild/clone"
	"github.com/anthonynsimon/bild/fcolor"
	"github.com/anthonynsimon/bild/math/f64"
	"github.com/anthonynsimon/bild/parallel"
)

// Normal combines the foreground and background images by placing the foreground over the
// background using alpha compositing. The resulting image is then returned.
func Normal(bg image.Image, fg image.Image) *image.RGBA {
	dst := blend(bg, fg, func(c0, c1 fcolor.RGBAF64) fcolor.RGBAF64 {
		return alphaComp(c0, c1)
	})

	return dst
}

// Add combines the foreground and background images by adding their values and
// returns the resulting image.
func Add(bg image.Image, fg image.Image) *image.RGBA {
	dst := blend(bg, fg, func(c0, c1 fcolor.RGBAF64) fcolor.RGBAF64 {
		r := c0.R + c1.R
		g := c0.G + c1.G
		b := c0.B + c1.B

		c2 := fcolor.RGBAF64{R: r, G: g, B: b, A: c1.A}
		return alphaComp(c0, c2)
	})

	return dst
}

// Multiply combines the foreground and background images by multiplying their
// normalized values and returns the resulting image.
func Multiply(bg image.Image, fg image.Image) *image.RGBA {
	dst := blend(bg, fg, func(c0, c1 fcolor.RGBAF64) fcolor.RGBAF64 {
		r := c0.R * c1.R
		g := c0.G * c1.G
		b := c0.B * c1.B

		c2 := fcolor.RGBAF64{R: r, G: g, B: b, A: c1.A}
		return alphaComp(c0, c2)
	})

	return dst
}

// Overlay combines the foreground and background images by using Multiply when channel values < 0.5
// or using Screen otherwise and returns the resulting image.
func Overlay(bg image.Image, fg image.Image) *image.RGBA {
	dst := blend(bg, fg, func(c0, c1 fcolor.RGBAF64) fcolor.RGBAF64 {
		var r, g, b float64
		if c0.R > 0.5 {
			r = 1 - (1-2*(c0.R-0.5))*(1-c1.R)
		} else {
			r = 2 * c0.R * c1.R
		}
		if c0.G > 0.5 {
			g = 1 - (1-2*(c0.G-0.5))*(1-c1.G)
		} else {
			g = 2 * c0.G * c1.G
		}
		if c0.B > 0.5 {
			b = 1 - (1-2*(c0.B-0.5))*(1-c1.B)
		} else {
			b = 2 * c0.B * c1.B
		}

		c2 := fcolor.RGBAF64{R: r, G: g, B: b, A: c1.A}
		return alphaComp(c0, c2)
	})

	return dst
}

// SoftLight combines the foreground and background images by using Pegtop's Soft Light formula and
// returns the resulting image.
func SoftLight(bg image.Image, fg image.Image) *image.RGBA {
	dst := blend(bg, fg, func(c0, c1 fcolor.RGBAF64) fcolor.RGBAF64 {
		r := (1-2*c1.R)*c0.R*c0.R + 2*c0.R*c1.R
		g := (1-2*c1.G)*c0.G*c0.G + 2*c0.G*c1.G
		b := (1-2*c1.B)*c0.B*c0.B + 2*c0.B*c1.B

		c2 := fcolor.RGBAF64{R: r, G: g, B: b, A: c1.A}
		return alphaComp(c0, c2)
	})
	return dst
}

// Screen combines the foreground and background images by inverting, multiplying and inverting the output.
// The result is a brighter image which is then returned.
func Screen(bg image.Image, fg image.Image) *image.RGBA {
	dst := blend(bg, fg, func(c0, c1 fcolor.RGBAF64) fcolor.RGBAF64 {
		r := 1 - (1-c0.R)*(1-c1.R)
		g := 1 - (1-c0.G)*(1-c1.G)
		b := 1 - (1-c0.B)*(1-c1.B)

		c2 := fcolor.RGBAF64{R: r, G: g, B: b, A: c1.A}
		return alphaComp(c0, c2)
	})

	return dst
}

// Difference calculates the absolute difference between the foreground and background images and
// returns the resulting image.
func Difference(bg image.Image, fg image.Image) *image.RGBA {
	dst := blend(bg, fg, func(c0, c1 fcolor.RGBAF64) fcolor.RGBAF64 {
		r := math.Abs(c0.R - c1.R)
		g := math.Abs(c0.G - c1.G)
		b := math.Abs(c0.B - c1.B)

		c2 := fcolor.RGBAF64{R: r, G: g, B: b, A: c1.A}
		return alphaComp(c0, c2)
	})

	return dst
}

// Divide combines the foreground and background images by diving the values from the background
// by the foreground and returns the resulting image.
func Divide(bg image.Image, fg image.Image) *image.RGBA {
	dst := blend(bg, fg, func(c0, c1 fcolor.RGBAF64) fcolor.RGBAF64 {
		var r, g, b float64
		if c1.R == 0 {
			r = 1
		} else {
			r = c0.R / c1.R
		}
		if c1.G == 0 {
			g = 1
		} else {
			g = c0.G / c1.G
		}
		if c1.B == 0 {
			b = 1
		} else {
			b = c0.B / c1.B
		}

		c2 := fcolor.RGBAF64{R: r, G: g, B: b, A: c1.A}
		return alphaComp(c0, c2)
	})

	return dst
}

// ColorBurn combines the foreground and background images by dividing the inverted
// background by the foreground image and then inverting the result which is then returned.
func ColorBurn(bg image.Image, fg image.Image) *image.RGBA {
	dst := blend(bg, fg, func(c0, c1 fcolor.RGBAF64) fcolor.RGBAF64 {
		var r, g, b float64
		if c1.R == 0 {
			r = 0
		} else {
			r = 1 - (1-c0.R)/c1.R
		}
		if c1.G == 0 {
			g = 0
		} else {
			g = 1 - (1-c0.G)/c1.G
		}
		if c1.B == 0 {
			b = 0
		} else {
			b = 1 - (1-c0.B)/c1.B
		}

		c2 := fcolor.RGBAF64{R: r, G: g, B: b, A: c1.A}
		return alphaComp(c0, c2)
	})

	return dst
}

// Exclusion combines the foreground and background images applying the Exclusion blend mode and
// returns the resulting image.
func Exclusion(bg image.Image, fg image.Image) *image.RGBA {
	dst := blend(bg, fg, func(c0, c1 fcolor.RGBAF64) fcolor.RGBAF64 {
		r := 0.5 - 2*(c0.R-0.5)*(c1.R-0.5)
		g := 0.5 - 2*(c0.G-0.5)*(c1.G-0.5)
		b := 0.5 - 2*(c0.B-0.5)*(c1.B-0.5)

		c2 := fcolor.RGBAF64{R: r, G: g, B: b, A: c1.A}
		return alphaComp(c0, c2)
	})

	return dst

}

// ColorDodge combines the foreground and background images by dividing background by the
// inverted foreground image and returns the result.
func ColorDodge(bg image.Image, fg image.Image) *image.RGBA {
	dst := blend(bg, fg, func(c0, c1 fcolor.RGBAF64) fcolor.RGBAF64 {
		var r, g, b float64
		if c1.R == 1 {
			r = 1
		} else {
			r = c0.R / (1 - c1.R)
		}
		if c1.G == 1 {
			g = 1
		} else {
			g = c0.G / (1 - c1.G)
		}
		if c1.B == 1 {
			b = 1
		} else {
			b = c0.B / (1 - c1.B)
		}

		c2 := fcolor.RGBAF64{R: r, G: g, B: b, A: c1.A}
		return alphaComp(c0, c2)
	})

	return dst
}

// LinearBurn combines the foreground and background images by adding them and
// then subtracting 255 (1.0 in normalized scale). The resulting image is then returned.
func LinearBurn(bg image.Image, fg image.Image) *image.RGBA {
	dst := blend(bg, fg, func(c0, c1 fcolor.RGBAF64) fcolor.RGBAF64 {
		r := c0.R + c1.R - 1
		g := c0.G + c1.G - 1
		b := c0.B + c1.B - 1

		c2 := fcolor.RGBAF64{R: r, G: g, B: b, A: c1.A}
		return alphaComp(c0, c2)
	})

	return dst
}

// LinearLight combines the foreground and background images by a mix of a Linear Dodge and
// Linear Burn operation. The resulting image is then returned.
func LinearLight(bg image.Image, fg image.Image) *image.RGBA {
	dst := blend(bg, fg, func(c0, c1 fcolor.RGBAF64) fcolor.RGBAF64 {
		var r, g, b float64
		if c1.R > 0.5 {
			r = c0.R + 2*c1.R - 0.5
		} else {
			r = c0.R + 2*c1.R - 1
		}
		if c1.G > 0.5 {
			g = c0.G + 2*c1.G - 0.5
		} else {
			g = c0.G + 2*c1.G - 1
		}
		if c1.B > 0.5 {
			b = c0.B + 2*c1.B - 0.5
		} else {
			b = c0.B + 2*c1.B - 1
		}

		c2 := fcolor.RGBAF64{R: r, G: g, B: b, A: c1.A}
		return alphaComp(c0, c2)
	})

	return dst
}

// Subtract combines the foreground and background images by Subtracting the background from the
// foreground. The result is then returned.
func Subtract(bg image.Image, fg image.Image) *image.RGBA {
	dst := blend(bg, fg, func(c0, c1 fcolor.RGBAF64) fcolor.RGBAF64 {
		r := c1.R - c0.R
		g := c1.G - c0.G
		b := c1.B - c0.B

		c2 := fcolor.RGBAF64{R: r, G: g, B: b, A: c1.A}
		return alphaComp(c0, c2)
	})

	return dst
}

// Opacity returns an image which blends the two input images by the percentage provided.
// Percent must be of range 0 <= percent <= 1.0
func Opacity(bg image.Image, fg image.Image, percent float64) *image.RGBA {
	percent = f64.Clamp(percent, 0, 1.0)

	dst := blend(bg, fg, func(c0, c1 fcolor.RGBAF64) fcolor.RGBAF64 {
		r := c1.R*percent + (1-percent)*c0.R
		g := c1.G*percent + (1-percent)*c0.G
		b := c1.B*percent + (1-percent)*c0.B

		c2 := fcolor.RGBAF64{R: r, G: g, B: b, A: c1.A}
		return alphaComp(c0, c2)
	})

	return dst
}

// Darken combines the foreground and background images by picking the darkest value per channel
// for each pixel. The result is then returned.
func Darken(bg image.Image, fg image.Image) *image.RGBA {
	dst := blend(bg, fg, func(c0, c1 fcolor.RGBAF64) fcolor.RGBAF64 {
		r := math.Min(c0.R, c1.R)
		g := math.Min(c0.G, c1.G)
		b := math.Min(c0.B, c1.B)

		c2 := fcolor.RGBAF64{R: r, G: g, B: b, A: c1.A}
		return alphaComp(c0, c2)
	})

	return dst
}

// Lighten combines the foreground and background images by picking the brightest value per channel
// for each pixel. The result is then returned.
func Lighten(bg image.Image, fg image.Image) *image.RGBA {
	dst := blend(bg, fg, func(c0, c1 fcolor.RGBAF64) fcolor.RGBAF64 {
		r := math.Max(c0.R, c1.R)
		g := math.Max(c0.G, c1.G)
		b := math.Max(c0.B, c1.B)

		c2 := fcolor.RGBAF64{R: r, G: g, B: b, A: c1.A}
		return alphaComp(c0, c2)
	})

	return dst
}

// Blend two images together by applying the provided function for each pixel.
// If images differ in size, the minimum width and height will be picked from each one
// when creating the resulting image.
func blend(bg image.Image, fg image.Image, fn func(fcolor.RGBAF64, fcolor.RGBAF64) fcolor.RGBAF64) *image.RGBA {
	bgBounds := bg.Bounds()
	fgBounds := fg.Bounds()

	var w, h int
	if bgBounds.Dx() < fgBounds.Dx() {
		w = bgBounds.Dx()
	} else {
		w = fgBounds.Dx()
	}
	if bgBounds.Dy() < fgBounds.Dy() {
		h = bgBounds.Dy()
	} else {
		h = fgBounds.Dy()
	}

	bgSrc := clone.AsRGBA(bg)
	fgSrc := clone.AsRGBA(fg)
	dst := image.NewRGBA(image.Rect(0, 0, w, h))

	parallel.Line(h, func(start, end int) {
		for y := start; y < end; y++ {
			for x := 0; x < w; x++ {
				bgPos := y*bgSrc.Stride + x*4
				fgPos := y*fgSrc.Stride + x*4
				result := fn(
					fcolor.NewRGBAF64(bgSrc.Pix[bgPos+0], bgSrc.Pix[bgPos+1], bgSrc.Pix[bgPos+2], bgSrc.Pix[bgPos+3]),
					fcolor.NewRGBAF64(fgSrc.Pix[fgPos+0], fgSrc.Pix[fgPos+1], fgSrc.Pix[fgPos+2], fgSrc.Pix[fgPos+3]))

				result.Clamp()
				dstPos := y*dst.Stride + x*4
				dst.Pix[dstPos+0] = uint8(result.R * 255)
				dst.Pix[dstPos+1] = uint8(result.G * 255)
				dst.Pix[dstPos+2] = uint8(result.B * 255)
				dst.Pix[dstPos+3] = uint8(result.A * 255)
			}

		}
	})

	return dst
}

// alphaComp returns a new color after compositing the two colors
// based on the foreground's alpha channel.
func alphaComp(bg, fg fcolor.RGBAF64) fcolor.RGBAF64 {
	fg.Clamp()
	fga := fg.A

	r := (fg.R * fga / 1) + ((1 - fga) * bg.R / 1)
	g := (fg.G * fga / 1) + ((1 - fga) * bg.G / 1)
	b := (fg.B * fga / 1) + ((1 - fga) * bg.B / 1)
	a := bg.A + fga

	return fcolor.RGBAF64{R: r, G: g, B: b, A: a}
}