func (cw *CustomWidget) bufferedPaint(canvas *Canvas, updateBounds Rectangle) error {
hdc := win.CreateCompatibleDC(canvas.hdc)
if hdc == 0 {
return newError("CreateCompatibleDC failed")
}
defer win.DeleteDC(hdc)
buffered := Canvas{hdc: hdc, doNotDispose: true}
if _, err := buffered.init(); err != nil {
return err
}
w, h := int32(updateBounds.Width), int32(updateBounds.Height)
if w < 1 {
w = 1
}
if h < 1 {
h = 1
}
hbmp := win.CreateCompatibleBitmap(canvas.hdc, w, h)
if hbmp == 0 {
return lastError("CreateCompatibleBitmap failed")
}
defer win.DeleteObject(win.HGDIOBJ(hbmp))
oldbmp := win.SelectObject(buffered.hdc, win.HGDIOBJ(hbmp))
if oldbmp == 0 {
return newError("SelectObject failed")
}
defer win.SelectObject(buffered.hdc, oldbmp)
win.SetViewportOrgEx(buffered.hdc, -int32(updateBounds.X), -int32(updateBounds.Y), nil)
win.SetBrushOrgEx(buffered.hdc, -int32(updateBounds.X), -int32(updateBounds.Y), nil)
err := cw.paint(&buffered, updateBounds)
if !win.BitBlt(canvas.hdc,
int32(updateBounds.X), int32(updateBounds.Y), w, h,
buffered.hdc,
int32(updateBounds.X), int32(updateBounds.Y), win.SRCCOPY) {
return lastError("buffered BitBlt failed")
}
return err
}
func hBitmapFromWindow(window Window) (win.HBITMAP, error) {
hdcMem := win.CreateCompatibleDC(0)
if hdcMem == 0 {
return 0, newError("CreateCompatibleDC failed")
}
defer win.DeleteDC(hdcMem)
var r win.RECT
if !win.GetWindowRect(window.Handle(), &r) {
return 0, newError("GetWindowRect failed")
}
hdc := win.GetDC(window.Handle())
width, height := r.Right-r.Left, r.Bottom-r.Top
hBmp := win.CreateCompatibleBitmap(hdc, width, height)
win.ReleaseDC(window.Handle(), hdc)
hOld := win.SelectObject(hdcMem, win.HGDIOBJ(hBmp))
flags := win.PRF_CHILDREN | win.PRF_CLIENT | win.PRF_ERASEBKGND | win.PRF_NONCLIENT | win.PRF_OWNED
window.SendMessage(win.WM_PRINT, uintptr(hdcMem), uintptr(flags))
win.SelectObject(hdcMem, hOld)
return hBmp, nil
}