short Escape(hdc, SET_SCREEN_ANGLE, sizeof(int),lpAngle, NULL)
The SET_SCREEN_ANGLE printer escape sets the current screen angle to the desired angle and enables an application to simulate the tilting of a photographic mask in producing a color separation for a particular primary.
hdc
HDC Identifies the device context.
lpAngle
LPINT Points to a short integer specifying the desired screen angle in tenths of a degree. The angle is measured counterclockwise.
The return value is the previous screen angle.
Four-color process separation is the process of separating the colors comprising an image into four component primaries: cyan, magenta, yellow, and black. The image is then reproduced by overprinting each primary.
In traditional four-color process printing, half-tone images for each of the four primaries are photographed against a mask tilted to a particular angle. Tilting the mask in this manner minimizes unwanted moir patterns caused by overprinting two or more colors.
The device driver defines the default screen angle.