改变映射模式就可以了SetMapMode
MM_ANISOTROPIC Logical units are converted to arbitrary units with arbitrarily scaled axes. Setting the mapping mode to MM_ANISOTROPIC does not change the current window or viewport settings. To change the units, orientation, and scaling, call the SetWindowExt and SetViewportExt member functions.
MM_HIENGLISH Each logical unit is converted to 0.001 inch. Positive x is to the right; positive y is up.
MM_HIMETRIC Each logical unit is converted to 0.01 millimeter. Positive x is to the right; positive y is up.
MM_ISOTROPIC Logical units are converted to arbitrary units with equally scaled axes; that is, 1 unit along the x-axis is equal to 1 unit along the y-axis. Use the SetWindowExt and SetViewportExt member functions to specify the desired units and the orientation of the axes. GDI makes adjustments as necessary to ensure that the x and y units remain the same size.
MM_LOENGLISH Each logical unit is converted to 0.01 inch. Positive x is to the right; positive y is up.
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.
MM_TWIPS Each logical unit is converted to 1/20 of a point. (Because a point is 1/72 inch, a twip is 1/1440 inch.) Positive x is to the right; positive y is up.