From b0b64e3610fbd421aa88dd5ce63fa73c875d0861 Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Sun, 2 Oct 2022 14:35:56 +0900
Subject: [PATCH] ebiten: use premultiplied-alpha format for ColorScale

Closes #2361
---
 colorscale.go  | 6 +-----
 shader_test.go | 2 +-
 2 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/colorscale.go b/colorscale.go
index 5e051879b..f800bb090 100644
--- a/colorscale.go
+++ b/colorscale.go
@@ -88,9 +88,5 @@ func (c *ColorScale) Scale(r, g, b, a float32) {
 // ScaleWithColor multiplies the given color values to the current scale.
 func (c *ColorScale) ScaleWithColor(clr color.Color) {
 	cr, cg, cb, ca := clr.RGBA()
-	if ca == 0 {
-		c.Scale(0, 0, 0, 0)
-		return
-	}
-	c.Scale(float32(cr)/float32(ca), float32(cg)/float32(ca), float32(cb)/float32(ca), float32(ca)/0xffff)
+	c.Scale(float32(cr)/0xffff, float32(cg)/0xffff, float32(cb)/0xffff, float32(ca)/0xffff)
 }
diff --git a/shader_test.go b/shader_test.go
index 174e116d4..ef6572ff0 100644
--- a/shader_test.go
+++ b/shader_test.go
@@ -1256,7 +1256,7 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 	op.ColorScale.SetG(5.0 / 8.0)
 	op.ColorScale.SetB(6.0 / 8.0)
 	op.ColorScale.SetA(7.0 / 8.0)
-	op.ColorScale.Scale(1.0/4.0, 2.0/4.0, 3.0/4.0, 4.0/4.0)
+	op.ColorScale.ScaleWithColor(color.RGBA{0x40, 0x80, 0xc0, 0xff})
 	dst.DrawRectShader(w, h, s, op)
 
 	for j := 0; j < h; j++ {