Name

eglSwapBuffers — post EGL surface color buffer to a native window

C Specification

EGLBoolean eglSwapBuffers( EGLDisplay display,
  EGLSurface surface);
 

Parameters

display

Specifies the EGL display connection.

surface

Specifies the EGL drawing surface whose buffers are to be swapped.

Description

If surface is a back-buffered window surface, eglSwapBuffers then the color buffer is copied (posted) native window associated with that surface. If surface is a single-buffered window, pixmap, or pixel buffer surface, eglSwapBuffers has no effect.

The contents of ancillary buffers are always undefined after calling eglSwapBuffers. The contents of the color buffer are undefined if the value of the EGL_SWAP_BEHAVIOR attribute of surface is not EGL_BUFFER_PRESERVED. The value of EGL_SWAP_BEHAVIOR can be set for some surfaces using eglSurfaceAttrib. EGL_SWAP_BEHAVIOR applies only to the color buffer. EGL has no way to specify or query whether or not ancillary buffers are preserved, and applications should not rely on this behavior.

eglSwapBuffers performs an implicit flush operation on the context (glFlush for an OpenGL ES or OpenGL context, vgFlush for an OpenVG context) bound to surface before swapping. Subsequent client API commands may be issued on that context immediately after calling eglSwapBuffers, but are not executed until the buffer exchange is completed.

Native Window Resizing

If the native window corresponding to surface has been resized prior to the swap, surface must be resized to match. surface will normally be resized by the EGL implementation at the time the native window is resized. If the implementation cannot do this transparently to the client, then eglSwapBuffers must detect the change and resize surface prior to copying its pixels to the native window. If surface shrinks as a result of resizing, some rendered pixels are lost. If surface grows, the newly allocated buffer contents are undefined. The resizing behavior described here only maintains consistency of EGL surfaces and native windows; clients are still responsible for detecting window size changes (using platform-specific means) and changing their viewport and scissor regions accordingly.

Notes

Attribute EGL_SWAP_BEHAVIOR is supported only if the EGL version is 1.2 or greater. In earlier versions, behavior is as though the attribute exists, and always has the value EGL_BUFFER_DESTROYED.

The EGL 1.4 specification was updated to acknowledge that ancillary buffers are not necessarily preserved after a swap, and that the EGL_SWAP_BEHAVIOR attribute applies only to the color buffer. This change in the specification acknowledged the behavior of many shipping implementations, and is not intended to result in behavior changes in any existing implementation.

Errors

EGL_FALSE is returned if swapping of the surface buffers fails, EGL_TRUE otherwise.

EGL_BAD_DISPLAY is generated if display is not an EGL display connection.

EGL_NOT_INITIALIZED is generated if display has not been initialized.

EGL_BAD_SURFACE is generated if surface is not an EGL drawing surface.

EGL_CONTEXT_LOST is generated if a power management event has occurred. The application must destroy all contexts and reinitialise OpenGL ES state and objects to continue rendering.

See Also

glFlush, eglCopyBuffers, vgFlush