Managing Graphics

Whenever possible be sure to use PolyTextOut, PolyPolyline, PolylineTo, PolyDraw, PolyBezier, and PolyBezierTo functions. These functions exploit the fact that many drawing calls use identical attributes, and so multiple items can be drawn in a single call once the brushes, pens, colors, and fonts have been selected. For example, the console window uses PolyTextOut. This change significantly reduces scrolling time in a console window.

If you are writing an application that draws on the display, then the CreateDIBSection function can improve performance. This function allows you to share a memory section directly with the system, and thus avoid having it copied from your process to the system each time there is a change. Previously, a common practice was to call the GetDIBits function, make the required changes, then call the SetDIBits function. These steps were often repeated on different scan lines of the bitmap before the image was ready for updating. Using CreateDIBSection is much simpler.

One word of caution if you decide to use CreateDIBSection. You need to be sure that any calls that might affect your bitmap have completed before you start to draw in it. This is because the batching of GDI calls may cause their delayed execution. For example, suppose you make a PatBlt call to clear your bitmap, then you start to change the bits in your DIB section. If the PatBlt call was batched, it might not actually execute until after you start to make the bitmap changes. So, before you make changes to your DIB section, be sure to call GdiFlush if you have made changes to the bitmap with earlier GDI calls.