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 (bmp *Bitmap) draw(hdc win.HDC, location Point) error {
return bmp.withSelectedIntoMemDC(func(hdcMem win.HDC) error {
size := bmp.Size()
if !win.BitBlt(
hdc,
int32(location.X),
int32(location.Y),
int32(size.Width),
int32(size.Height),
hdcMem,
0,
0,
win.SRCCOPY) {
return lastError("BitBlt")
}
return nil
})
}