[Mesa3d-users] Mesa7.5.1, Win32, GDI, Rubberbanding/glFlush() Problem

[Randolf S. <ran...@gm...>]

Greetings,

my rubberbanding code fails with Mesa7.5.1/Win32/GDI.
The code draws with XOR directly to the front buffer,
an looks like this:
-snip-
glDrawBuffer(GL_FRONT);
glEnable(GL_COLOR_LOGIC_OP);
glLogicOp(GL_XOR);
glDisable(GL_DEPTH_TEST);

// actual drawing using glBegin() glVertex() and friends omitted

glEnable(GL_DEPTH_TEST);
glLogicOp(GL_COPY);
glDisable(GL_COLOR_LOGIC_OP);
glFlush();
glDrawBuffer(GL_BACK);
-snap-

The rubberband is drawn but immediately cleared.
This is because in
wmesa.c:write_rgba_span_front()
a BitBlt() occurs, that directly draws the rubberband,
and in the glFlush()
wmesa.c:wmesa_flush()
another BitBlt() is done, that erases everything.

Can we maybe check in wmesa_flush() whether
the current buffer is the front buffer and do not do
anything if this is the case (no idea whether this
would affect drawing to the front buffer _without_
logic op enabled, those functions must then also
BitBlt directly...)?
Or should write_rgba_span_front() draw to a different
place, that is later copied to the screen in
wmesa_flush()?

On my side, I can make my code work by omitting
the glFlush(), however, I am hesitant to do so, because
if the application runs over a network, a glFlush()
seems quite appropriate for the special use case of
rubberbanding.

kind regards,
Randolf