ui: More accurate device scale factor

internal/ui/ui_glfw.go

@@ -147,16 +147,8 @@ func (u *userInterface) Start(width, height, scale int, title string) error {
 		m := glfw.GetPrimaryMonitor()
 		v := m.GetVideoMode()
 		mw, _ := m.GetPhysicalSize()
-		u.deviceScale = 1
+		u.deviceScale = deviceScale()
 		u.framebufferScale = 1
-		// mw can be 0 on some environment like Linux VM
-		if 0 < mw {
-			dpi := float64(v.Width) * 25.4 / float64(mw)
-			u.deviceScale = dpi / 96
-			if u.deviceScale < 1 {
-				u.deviceScale = 1
-			}
-		}
 
 		if !u.setScreenSize(width, height, scale) {
 			err = errors.New("ui: Fail to set the screen size")

internal/ui/ui_linux.go

@@ -0,0 +1,22 @@
+// 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 !js
+
+package ui
+
+func deviceScale() float64 {
+	// TODO: Implement this
+	return 1
+}

internal/ui/ui_mac.go

@@ -0,0 +1,25 @@
+// 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 darwin,!arm,!arm64
+// +build !js
+// +build !ios
+
+package ui
+
+func deviceScale() float64 {
+	// The device scale is always 1 on Mac OS.
+	// The frame buffer size is different from the window size.
+	return 1
+}

internal/ui/ui_windows.go

@@ -0,0 +1,32 @@
+// 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 !js
+
+package ui
+
+// #cgo LDFLAGS: -lgdi32
+//
+// #include <windows.h>
+//
+// static int getDPI() {
+//   HDC dc = GetWindowDC(0);
+//   return GetDeviceCaps(dc, LOGPIXELSX);
+// }
+import "C"
+
+func deviceScale() float64 {
+	dpi := int(C.getDPI())
+	return float64(dpi) / 96
+}