ui: Bug fix: Adjust scaling factor on Linux (#157)

internal/ui/scaling.go

@@ -0,0 +1,23 @@
+// Copyright 2016 Hajime Hoshi
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build !linux
+
+package ui
+
+func adjustScaleForGLFW(scale int) int {
+	// On Windows and OSX, GLFW already considers High-DPI scaling
+	// and scale doesn't have to be adjusted.
+	return scale
+}

internal/ui/scaling_linux.go

@@ -0,0 +1,49 @@
+// Copyright 2016 Hajime Hoshi
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package ui
+
+import (
+	"fmt"
+	"os/exec"
+	"regexp"
+	"strconv"
+)
+
+var scalingFactorSyntax = regexp.MustCompile(`\Auint32\s+(\d+)\s*\z`)
+var deviceScaleFactor = 0
+
+// adjustScaleForGLFW adjusts the given scale which is passed to the GLFW API.
+func adjustScaleForGLFW(scale int) int {
+	if 0 < deviceScaleFactor {
+		return scale * deviceScaleFactor
+	}
+	// Execute gsettings command instead of calling gtk functions so as not to depend on
+	// gobject-2.0 library.
+	c := exec.Command("gsettings", "get", "org.gnome.desktop.interface", "scaling-factor")
+	o, err := c.Output()
+	if err != nil {
+		panic(fmt.Sprintf("graphics: executing gsettings error %v", err))
+	}
+	m := scalingFactorSyntax.FindStringSubmatch(string(o))
+	if m == nil {
+		panic("graphics: gsettings result syntax is not expected")
+	}
+	s, err := strconv.Atoi(m[1])
+	if err != nil {
+		panic(fmt.Sprintf("graphics: %v", err))
+	}
+	deviceScaleFactor = s
+	return scale * deviceScaleFactor
+}

internal/ui/ui_glfw.go

@@ -108,13 +108,13 @@ type userInterface struct {
 }
 
 func (u *userInterface) start(width, height, scale int, title string) (actualScale int, err error) {
-	videoMode := glfw.GetPrimaryMonitor().GetVideoMode()
-	x := (videoMode.Width - width*scale) / 2
-	y := (videoMode.Height - height*scale) / 3
-
 	u.setScreenSize(width, height, scale)
 	u.window.SetTitle(title)
 	u.window.Show()
+
+	videoMode := glfw.GetPrimaryMonitor().GetVideoMode()
+	x := (videoMode.Width - width*adjustScaleForGLFW(scale)) / 2
+	y := (videoMode.Height - height*adjustScaleForGLFW(scale)) / 3
 	u.window.SetPos(x, y)
 
 	return u.actualScale, nil
@@ -158,7 +158,7 @@ func (u *userInterface) setScreenSize(width, height, scale int) bool {
 	}
 
 	// To make sure the current existing framebuffers are rendered,
-	// swap buffers here.
+	// swap buffers here before SetSize is called.
 	u.context.BindZeroFramebuffer()
 	u.swapBuffers()
 
@@ -168,7 +168,7 @@ func (u *userInterface) setScreenSize(width, height, scale int) bool {
 		window.SetFramebufferSizeCallback(nil)
 		close(ch)
 	})
-	window.SetSize(width*scale, height*scale)
+	window.SetSize(width*adjustScaleForGLFW(scale), height*adjustScaleForGLFW(scale))
 
 event:
 	for {