rhi: gl: Do not bother with glDrawBuffers(GL_BACK)

It's per framebuffer and the color target for the default fbo
is never altered. So no need for this call. This is useful because
it avoids having to deal with the controversy around GL_BACK (where
the GL, but not the ES, spec claims some quite nonsensical things
about GL_BACK not being accepted by glDrawBuffers (in the name of
stereo support?), nevermind GL_BACK being the default value...),
and while what we have in place now seems to be ok with many
implementations, it may generate a GL error with others - so
just remove the call in order not have to think about this
legacy nonsense)

Task-number: QTBUG-88070
Change-Id: I051c60a3041865a3434801b57da2b7acb518b8fe
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

1 files changed, 0 insertions, 4 deletions

diff --git a/src/gui/rhi/qrhigles2.cpp b/src/gui/rhi/qrhigles2.cpp
index 785c341a0f..3ebc0f9182 100644
--- a/src/gui/rhi/qrhigles2.cpp
+++ b/src/gui/rhi/qrhigles2.cpp
@@ -2399,10 +2399,6 @@ void QRhiGles2::executeCommandBuffer(QRhiCommandBuffer *cb)
                 }
             } else {
                 f->glBindFramebuffer(GL_FRAMEBUFFER, ctx->defaultFramebufferObject());
-                if (caps.maxDrawBuffers > 1) {
-                    GLenum bufs = GL_BACK;
-                    f->glDrawBuffers(1, &bufs);
-                }
             }
             if (caps.srgbCapableDefaultFramebuffer) {
                 if (cmd.args.bindFramebuffer.srgb)