graphics: Refactoring: Move adjustment logic for glClearColor to opengl package

internal/graphics/command.go

@@ -205,28 +205,6 @@ func (c *fillCommand) Exec(indexOffsetInBytes int) error {
 	g := float32(cg) / max
 	b := float32(cb) / max
 	a := float32(ca) / max
-
-	// On some machines like MacBook Pro, exact 0 and exact 1 might cause problems
-	// at glClear() (#452).
-	if r == 0 {
-		r = math.Nextafter32(r, 1)
-	}
-	if g == 0 {
-		g = math.Nextafter32(g, 1)
-	}
-	if b == 0 {
-		b = math.Nextafter32(b, 1)
-	}
-	if r == 1 {
-		r = math.Nextafter32(r, 0)
-	}
-	if g == 1 {
-		g = math.Nextafter32(g, 0)
-	}
-	if b == 1 {
-		b = math.Nextafter32(b, 0)
-	}
-
 	if err := opengl.GetContext().FillFramebuffer(r, g, b, a); err != nil {
 		return err
 	}

internal/math/math.go

@@ -14,6 +14,7 @@
 
 package math
 
+// NextPowerOf2Int returns a nearest power of 2 to x.
 func NextPowerOf2Int(x int) int {
 	if x <= 0 {
 		panic("x must be positive")

internal/opengl/context.go

@@ -14,6 +14,34 @@
 
 package opengl
 
+import (
+	"math"
+)
+
+var (
+	zeroPlus float32
+	oneMinus float32
+)
+
+func init() {
+	zeroPlus = math.Nextafter32(0, 1)
+	oneMinus = math.Nextafter32(1, 0)
+}
+
+// adjustForClearColor adjust the value x for glClearColor function.
+//
+// On some machines like MacBook Pro, exact 0 and exact 1 might cause problems
+// at glClear() (#452).
+func adjustForClearColor(x float32) float32 {
+	if x <= 0 {
+		return zeroPlus
+	}
+	if x >= 1 {
+		return oneMinus
+	}
+	return x
+}
+
 var (
 	Nearest            Filter
 	Linear             Filter

internal/opengl/context_desktop.go

@@ -283,7 +283,10 @@ func (c *Context) setViewportImpl(width, height int) {
 
 func (c *Context) FillFramebuffer(r, g, b, a float32) error {
 	return c.runOnContextThread(func() error {
-		gl.ClearColor(r, g, b, a)
+		gl.ClearColor(adjustForClearColor(r),
+			adjustForClearColor(g),
+			adjustForClearColor(b),
+			adjustForClearColor(a))
 		gl.Clear(gl.COLOR_BUFFER_BIT)
 		return nil
 	})

internal/opengl/context_js.go

@@ -255,7 +255,10 @@ func (c *Context) setViewportImpl(width, height int) {
 func (c *Context) FillFramebuffer(r, g, b, a float32) error {
 	// TODO: Use f?
 	gl := c.gl
-	gl.ClearColor(r, g, b, a)
+	gl.ClearColor(adjustForClearColor(r),
+		adjustForClearColor(g),
+		adjustForClearColor(b),
+		adjustForClearColor(a))
 	gl.Clear(gl.COLOR_BUFFER_BIT)
 	return nil
 }

internal/opengl/context_mobile.go

@@ -222,7 +222,10 @@ func (c *Context) setViewportImpl(width, height int) {
 
 func (c *Context) FillFramebuffer(r, g, b, a float32) error {
 	gl := c.gl
-	gl.ClearColor(r, g, b, a)
+	gl.ClearColor(adjustForClearColor(r),
+		adjustForClearColor(g),
+		adjustForClearColor(b),
+		adjustForClearColor(a))
 	gl.Clear(mgl.COLOR_BUFFER_BIT)
 	return nil
 }