最近在做一個繪圖應用，經常會在除錯的時候看到QPainter::begin: Paint device returned engine == 0, type:1/2/3之類的警告。一直對type代表的具體內容不解，前幾天看了看QPainter的原始碼，恍然大悟~

d->engine = pd->paintEngine();

    if (!d->engine) {
        qWarning("QPainter::begin: Paint device returned engine == 0, type: %d", pd->devType());
        return false;
    }
 

    在這裡找到了這個警告的原型，然後跟蹤pd->devType()

int QImage::devType() const
{
    return QInternal::Image;
}

class Q_CORE_EXPORT QInternal {
public:
    enum PaintDeviceFlags {
        UnknownDevice = 0x00,
        Widget        = 0x01,
        Pixmap        = 0x02,
        Image         = 0x03,
        Printer       = 0x04,
        Picture       = 0x05,
        Pbuffer       = 0x06,    // GL pbuffer
        FramebufferObject = 0x07, // GL framebuffer object
        CustomRaster  = 0x08,
        MacQuartz     = 0x09,
        PaintBuffer   = 0x0a,
        OpenGL        = 0x0b
    };