func withCompatibleDC(f func(hdc win.HDC) error) error {
hdc := win.CreateCompatibleDC(0)
if hdc == 0 {
return newError("CreateCompatibleDC failed")
}
defer win.DeleteDC(hdc)
return f(hdc)
}
func (c *Canvas) Dispose() {
if !c.doNotDispose && c.hdc != 0 {
if c.hwnd == 0 {
win.DeleteDC(c.hdc)
} else {
win.ReleaseDC(c.hwnd, c.hdc)
}
c.hdc = 0
}
if c.recordingMetafile != nil {
c.recordingMetafile.ensureFinished()
c.recordingMetafile = nil
}
if c.measureTextMetafile != nil {
c.measureTextMetafile.Dispose()
c.measureTextMetafile = nil
}
}
func NewCanvasFromImage(image Image) (*Canvas, error) {
switch img := image.(type) {
case *Bitmap:
hdc := win.CreateCompatibleDC(0)
if hdc == 0 {
return nil, newError("CreateCompatibleDC failed")
}
succeeded := false
defer func() {
if !succeeded {
win.DeleteDC(hdc)
}
}()
if win.SelectObject(hdc, win.HGDIOBJ(img.hBmp)) == 0 {
return nil, newError("SelectObject failed")
}
succeeded = true
return (&Canvas{hdc: hdc}).init()
case *Metafile:
c, err := newCanvasFromHDC(img.hdc)
if err != nil {
return nil, err
}
c.recordingMetafile = img
return c, nil
}
return nil, newError("unsupported image type")
}