Support glfw.TransparentFramebuffer window hint

CHANGELOG.md

@@ -5,6 +5,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 ## [Unreleased]
 - Gamepad API?
+- Add `WindowConfig.TransparentFramebuffer` option to support window transparency onto the background
 
 ## [v0.10.0-alpha] 2020-05-08
 - Upgrade to GLFW 3.3! :tada:

pixelgl/window.go

@@ -56,6 +56,12 @@ type WindowConfig struct {
 	// implement proper full screen windows.
 	AlwaysOnTop bool
 
+	// TransparentFramebuffer specifies whether the window framebuffer will be
+	// transparent. If enabled and supported by the system, the window
+	// framebuffer alpha channel will be used to combine the framebuffer with
+	// the background. This does not affect window decorations.
+	TransparentFramebuffer bool
+
 	// VSync (vertical synchronization) synchronizes Window's framerate with the framerate of
 	// the monitor.
 	VSync bool
@@ -112,6 +118,7 @@ func NewWindow(cfg WindowConfig) (*Window, error) {
 		glfw.WindowHint(glfw.Decorated, bool2int[!cfg.Undecorated])
 		glfw.WindowHint(glfw.Floating, bool2int[cfg.AlwaysOnTop])
 		glfw.WindowHint(glfw.AutoIconify, bool2int[!cfg.NoIconify])
+		glfw.WindowHint(glfw.TransparentFramebuffer, bool2int[cfg.TransparentFramebuffer])
 
 		var share *glfw.Window
 		if currWin != nil {