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devicescale: Use NewLazyDLL on Windows

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This commit is contained in:
Hajime Hoshi 2018-01-03 16:24:53 +09:00
parent 7b759faf36
commit 0f450fb1e2
1 changed files with 48 additions and 19 deletions
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67
internal/devicescale/devicescale_windows.go
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@ -16,33 +16,23 @@
package devicescale
// TODO: Use golang.org/x/sys/windows (NewLazyDLL) instead of cgo.
// #cgo LDFLAGS: -lgdi32
//
// #include <windows.h>
//
// static char* getDPI(int* dpi) {
// HDC dc = GetWindowDC(0);
// *dpi = GetDeviceCaps(dc, LOGPIXELSX);
// if (!ReleaseDC(0, dc)) {
// return "ReleaseDC failed";
// }
// return "";
// }
import "C"
import (
"fmt"
"syscall"
)
const logPixelSx = 88
var (
user32 = syscall.NewLazyDLL("user32")
gdi32 = syscall.NewLazyDLL("gdi32")
)
var (
procSetProcessDPIAware = user32.NewProc("SetProcessDPIAware")
procGetWindowDC = user32.NewProc("GetWindowDC")
procReleaseDC = user32.NewProc("ReleaseDC")
procGetDeviceCaps = gdi32.NewProc("GetDeviceCaps")
)
func setProcessDPIAware() error {
@ -56,13 +46,52 @@ func setProcessDPIAware() error {
return nil
}
func getWindowDC(hwnd uintptr) (uintptr, error) {
r, _, e := syscall.Syscall(procGetWindowDC.Addr(), 1, hwnd, 0, 0)
if e != 0 {
return 0, fmt.Errorf("devicescale: GetWindowDC failed: error code: %d", e)
}
if r == 0 {
return 0, fmt.Errorf("devicescale: GetWindowDC failed: returned value: %d", r)
}
return r, nil
}
func releaseDC(hwnd, hdc uintptr) error {
r, _, e := syscall.Syscall(procReleaseDC.Addr(), 2, hwnd, hdc, 0)
if e != 0 {
return fmt.Errorf("devicescale: ReleaseDC failed: error code: %d", e)
}
if r == 0 {
return fmt.Errorf("devicescale: ReleaseDC failed: returned value: %d", r)
}
return nil
}
func getDeviceCaps(hdc uintptr, nindex int) (int, error) {
r, _, e := syscall.Syscall(procGetDeviceCaps.Addr(), 2, hdc, uintptr(nindex), 0)
if e != 0 {
return 0, fmt.Errorf("devicescale: GetDeviceCaps failed: error code: %d", e)
}
return int(r), nil
}
func impl() float64 {
if err := setProcessDPIAware(); err != nil {
panic(err)
}
dpi := C.int(0)
if errmsg := C.GoString(C.getDPI(&dpi)); errmsg != "" {
panic(errmsg)
dc, err := getWindowDC(0)
if err != nil {
panic(err)
}
dpi, err := getDeviceCaps(dc, logPixelSx)
if err != nil {
panic(err)
}
if err := releaseDC(0, dc); err != nil {
panic(err)
}
return float64(dpi) / 96
}