关于内存DC中绘图，我有问题，哪位给解决一下

[KissYou]

我们都知道，可以在OnDraw中创建一个内存 DC，然后产生一个与显示设备兼容的位图，当把这个位图选入这个内存DC中以后，我们可以在这个内存DC中用GDI函数绘图，最后把位图拷贝到显示设备中。
这样做有一个问题，当我设置我的原始场境(即OnDraw的pDC)映射模式为MM_LOMETRIC时，这样做就不行。结果位图并没有被拷贝。请问这是为什么？

[joke100]

位传送是设备点,也就是以像素为单位,改变成这种逻辑单位会影响???

[ShowMan]

帮你查了一下MSDN,MAP MODE 应当有影响. 拷贝MSDN原话,无暇翻译.
MM_LOMETRIC Each logical unit is converted to 0.1 millimeter. Positive x is to the right; positive y is up.
MM_TEXT Each logical unit is converted to 1 device pixel. Positive x is to the right; positive y is down.
Sets the mapping mode. The mapping mode defines the unit of measure used to convert logical units to device units; it also defines the orientation of the device抯 x- and y-axes. GDI uses the mapping mode to convert logical coordinates into the appropriate device coordinates. The MM_TEXT mode allows applications to work in device pixels, where 1 unit is equal to 1 pixel. The physical size of a pixel varies from device to device.

[weizhisheng]

只是MM_LOMETRIC模式不行吗，如果除了MM_TEXT其他的模式都不行，那就是你忘记了y坐标方向的问题。建议再用其他映射模式看看。