Add a raw bind() function to QGLBuffer.

It is awkward for a Qt application to do the equivalent of
glBindBuffer(GL_ARRAY_BUFFER, 0) without knowing the QGLBuffer
that was previously bound, or to bind a raw id obtained elsewhere.
Resolving the extension is annoying.

This change provides a raw low-level version of bind() for directly
resolving and calling glBindBuffer() to assist such applications.

Reviewed-by: Sarah Smith

2 files changed, 34 insertions, 0 deletions

diff --git a/src/opengl/qglbuffer.cpp b/src/opengl/qglbuffer.cpp
index 7022a53..2ab7c32 100644
--- a/src/opengl/qglbuffer.cpp
+++ b/src/opengl/qglbuffer.cpp
@@ -369,6 +369,38 @@ void QGLBuffer::release() const
         glBindBuffer(d->type, 0);
 }
 
+#undef ctx
+
+/*!
+    Binds a raw \a bufferId to the specified buffer \a type
+    in the current QGLContext.  Returns false if there is
+    no context current or the GL buffer extension could
+    not be resolved.
+
+    This function is a direct call to \c{glBindBuffer()} for
+    use when the caller does not have a QGLBuffer but does
+    have a raw \a bufferId.  It can also be used to release
+    the current buffer when the caller does not know which
+    QGLBuffer object is currently bound:
+
+    \code
+    QGLBuffer::bind(QGLBuffer::VertexBuffer, 0);
+    \endcode
+*/
+bool QGLBuffer::bind(QGLBuffer::Type type, uint bufferId)
+{
+    const QGLContext *ctx = QGLContext::currentContext();
+    if (ctx) {
+        if (qt_resolve_buffer_extensions(const_cast<QGLContext *>(ctx))) {
+            glBindBuffer(GLenum(type), GLuint(bufferId));
+            return true;
+        }
+    }
+    return false;
+}
+
+#define ctx d->guard.context()
+
 /*!
     Returns the GL identifier associated with this buffer; zero if
     the buffer has not been created.
diff --git a/src/opengl/qglbuffer.h b/src/opengl/qglbuffer.h
index ecb86e2..a060733 100644
--- a/src/opengl/qglbuffer.h
+++ b/src/opengl/qglbuffer.h
@@ -97,6 +97,8 @@ public:
     bool bind() const;
     void release() const;
 
+    static bool bind(QGLBuffer::Type type, uint bufferId);
+
     uint bufferId() const;
 
     int size() const;