Merge pull request #81 from BluePsyduck/export-blend

Make blend() exported to allow for custom blending implementations.

blend/blend.go

@@ -14,7 +14,7 @@ import (
 // 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 {
+	dst := Blend(bg, fg, func(c0, c1 fcolor.RGBAF64) fcolor.RGBAF64 {
 		return alphaComp(c0, c1)
 	})
 
@@ -24,7 +24,7 @@ func Normal(bg image.Image, fg image.Image) *image.RGBA {
 // 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 {
+	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
@@ -39,7 +39,7 @@ func Add(bg image.Image, fg image.Image) *image.RGBA {
 // 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 {
+	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
@@ -54,7 +54,7 @@ func Multiply(bg image.Image, fg image.Image) *image.RGBA {
 // 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 {
+	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)
@@ -82,7 +82,7 @@ func Overlay(bg image.Image, fg image.Image) *image.RGBA {
 // 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 {
+	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
@@ -96,7 +96,7 @@ func SoftLight(bg image.Image, fg image.Image) *image.RGBA {
 // 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 {
+	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)
@@ -111,7 +111,7 @@ func Screen(bg image.Image, fg image.Image) *image.RGBA {
 // 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 {
+	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)
@@ -126,7 +126,7 @@ func Difference(bg image.Image, fg image.Image) *image.RGBA {
 // 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 {
+	dst := Blend(bg, fg, func(c0, c1 fcolor.RGBAF64) fcolor.RGBAF64 {
 		var r, g, b float64
 		if c1.R == 0 {
 			r = 1
@@ -154,7 +154,7 @@ func Divide(bg image.Image, fg image.Image) *image.RGBA {
 // 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 {
+	dst := Blend(bg, fg, func(c0, c1 fcolor.RGBAF64) fcolor.RGBAF64 {
 		var r, g, b float64
 		if c1.R == 0 {
 			r = 0
@@ -182,7 +182,7 @@ func ColorBurn(bg image.Image, fg image.Image) *image.RGBA {
 // 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 {
+	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)
@@ -198,7 +198,7 @@ func Exclusion(bg image.Image, fg image.Image) *image.RGBA {
 // 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 {
+	dst := Blend(bg, fg, func(c0, c1 fcolor.RGBAF64) fcolor.RGBAF64 {
 		var r, g, b float64
 		if c1.R == 1 {
 			r = 1
@@ -226,7 +226,7 @@ func ColorDodge(bg image.Image, fg image.Image) *image.RGBA {
 // 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 {
+	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
@@ -241,7 +241,7 @@ func LinearBurn(bg image.Image, fg image.Image) *image.RGBA {
 // 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 {
+	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
@@ -269,7 +269,7 @@ func LinearLight(bg image.Image, fg image.Image) *image.RGBA {
 // 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 {
+	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
@@ -286,7 +286,7 @@ func Subtract(bg image.Image, fg image.Image) *image.RGBA {
 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 {
+	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
@@ -301,7 +301,7 @@ func Opacity(bg image.Image, fg image.Image, percent float64) *image.RGBA {
 // 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 {
+	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)
@@ -316,7 +316,7 @@ func Darken(bg image.Image, fg image.Image) *image.RGBA {
 // 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 {
+	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)
@@ -331,7 +331,7 @@ func Lighten(bg image.Image, fg image.Image) *image.RGBA {
 // 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 {
+func Blend(bg image.Image, fg image.Image, fn func(fcolor.RGBAF64, fcolor.RGBAF64) fcolor.RGBAF64) *image.RGBA {
 	bgBounds := bg.Bounds()
 	fgBounds := fg.Bounds()