wglMakeCurrent

The wglMakeCurrent function makes a specified OpenGL rendering context the calling thread's current rendering context. All subsequent OpenGL calls made by the thread are drawn on the device identified by hdc. You can also use wglMakeCurrent to change the calling thread's current rendering context so it's no longer current.

BOOL wglMakeCurrent(
  HDC  hdc,      // device context of device that OpenGL calls are 
                 // to be drawn on
  HGLRC  hglrc   // OpenGL rendering context to be made the calling 
                 // thread's current rendering context
);

Parameters

• hdc
  Handle to a device context. Subsequent OpenGL calls made by the calling thread are drawn on the device identified by hdc.

• hglrc
  Handle to an OpenGL rendering context that the function sets as the calling thread's rendering context.

  If hglrc is NULL, the function makes the calling thread's current rendering context no longer current, and releases the device context that is used by the rendering context. In this case, hdc is ignored.

Return Values

When the wglMakeCurrent function succeeds, the return value is TRUE; otherwise the return value is FALSE. To get extended error information, call GetLastError.

Remarks

The hdc parameter must refer to a drawing surface supported by OpenGL. It need not be the same hdc that was passed to wglCreateContext when hglrc was created, but it must be on the same device and have the same pixel format. GDI transformation and clipping in hdc are not supported by the rendering context. The current rendering context uses the hdc device context until the rendering context is no longer current.

Before switching to the new rendering context, OpenGL flushes any previous rendering context that was current to the calling thread.

A thread can have one current rendering context. A process can have multiple rendering contexts by means of multithreading. A thread must set a current rendering context before calling any OpenGL functions. Otherwise, all OpenGL calls are ignored.

A rendering context can be current to only one thread at a time. You cannot make a rendering context current to multiple threads.

An application can perform multithread drawing by making different rendering contexts current to different threads, supplying each thread with its own rendering context and device context.

If an error occurs, the wglMakeCurrent function makes the thread's current rendering context not current before returning.

Requirements

**  Windows NT/2000:** Requires Windows NT 3.5 or later.
**  Windows 95/98:** Requires Windows 95 or later. Available as a redistributable for Windows 95.
**  Header:** Declared in wingdi.h.
**  Import Library:** Use opengl32.lib.

See Also

OpenGL on Windows NT, Windows 2000, and Windows 95/98, WGL Functions, wglCreateContext, wglDeleteContext, wglGetCurrentContext, wglGetCurrentDC