opengl: Cache a composition mode

internal/graphics/opengl/context_desktop.go

@@ -49,6 +49,7 @@ func (p Program) id() programID {
 type context struct {
 	locationCache       *locationCache
 	funcs               chan func()
+	lastCompositionMode CompositionMode
 }
 
 func NewContext() *Context {
@@ -72,6 +73,7 @@ func NewContext() *Context {
 	}
 	c.locationCache = newLocationCache()
 	c.funcs = make(chan func())
+	c.lastCompositionMode = CompositionModeUnknown
 	return c
 }
 
@@ -110,8 +112,11 @@ func (c *Context) Init() {
 
 func (c *Context) BlendFunc(mode CompositionMode) {
 	c.RunOnContextThread(func() {
+		if c.lastCompositionMode == mode {
+			return
+		}
+		c.lastCompositionMode = mode
 		s, d := c.operations(mode)
-		// TODO: Cache and don't call this often
 		gl.BlendFunc(uint32(s), uint32(d))
 	})
 }

internal/graphics/opengl/context_js.go

@@ -67,6 +67,7 @@ type context struct {
 	lastFramebuffer     Framebuffer
 	locationCache       *locationCache
 	lastProgramID       programID
+	lastCompositionMode CompositionMode
 }
 
 func NewContext() *Context {
@@ -114,6 +115,7 @@ func NewContext() *Context {
 	}
 	c.gl = gl
 	c.locationCache = newLocationCache()
+	c.lastCompositionMode = CompositionModeUnknown
 	c.init()
 	return c
 }
@@ -127,8 +129,11 @@ func (c *Context) init() {
 }
 
 func (c *Context) BlendFunc(mode CompositionMode) {
+	if c.lastCompositionMode == mode {
+		return
+	}
+	c.lastCompositionMode = mode
 	s, d := c.operations(mode)
-	// TODO: Cache and don't call this often
 	gl := c.gl
 	gl.BlendFunc(int(s), int(d))
 }

internal/graphics/opengl/types.go

@@ -44,7 +44,7 @@ type Context struct {
 type CompositionMode int
 
 const (
-	CompositionModeSourceOver CompositionMode = iota
+	CompositionModeSourceOver CompositionMode = iota // This value must be 0 (= initial value)
 	CompositionModeClear
 	CompositionModeCopy
 	CompositionModeDesination
@@ -57,6 +57,7 @@ const (
 	CompositionModeDestinationAtop
 	CompositionModeXor
 	CompositionModeLighter
+	CompositionModeUnknown
 )
 
 func (c *Context) operations(mode CompositionMode) (src operation, dst operation) {