Add support for glMapBufferRange in the wrappers and resolvers

QOpenGLBuffer::map() and related helpers are becoming useless in
OpenGL ES 3.0 and up: instead of the old GL_OES_map_buffer,
glMapBufferRange, but not glMapBuffer, is now part of the standard.
On desktop GL_ARB_map_buffer_range is present by default in OpenGL 3.0
and newer.

[ChangeLog][QtGui] Added QOpenGLBuffer::mapBufferRange().

Task-number: QTBUG-38168
Change-Id: I4e9bbe8ced9ee4d535ac32849a8c08c26d79cb49
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>

4 files changed, 122 insertions, 8 deletions

diff --git a/src/gui/opengl/qopenglbuffer.cpp b/src/gui/opengl/qopenglbuffer.cpp
index a8a2255104..3ae45abb11 100644
--- a/src/gui/opengl/qopenglbuffer.cpp
+++ b/src/gui/opengl/qopenglbuffer.cpp
@@ -128,6 +128,18 @@ QT_BEGIN_NAMESPACE
     \value ReadWrite The buffer will be mapped for reading and writing.
 */
 
+/*!
+    \enum QOpenGLBuffer::RangeAccessFlag
+    This enum defines the access mode bits for QOpenGLBuffer::mapRange().
+
+    \value RangeRead The buffer will be mapped for reading.
+    \value RangeWrite The buffer will be mapped for writing.
+    \value RangeInvalidate Discard the previous contents of the specified range.
+    \value RangeInvalidateBuffer Discard the previous contents of the entire buffer.
+    \value RangeFlushExplicit Indicates that modifications are to be flushed explicitly via \c glFlushMappedBufferRange.
+    \value RangeUnsynchronized Indicates that pending operations should not be synchronized before returning from mapRange().
+*/
+
 class QOpenGLBufferPrivate
 {
 public:
@@ -514,10 +526,14 @@ int QOpenGLBuffer::size() const
     It is assumed that create() has been called on this buffer and that
     it has been bound to the current context.
 
-    This function is only supported under OpenGL/ES if the
-    \c{GL_OES_mapbuffer} extension is present.
+    \note This function is only supported under OpenGL ES 2.0 or
+    earlier if the \c GL_OES_mapbuffer extension is present.
 
-    \sa unmap(), create(), bind()
+    \note On OpenGL ES 3.0 and newer, or, in case if desktop OpenGL,
+    if \c GL_ARB_map_buffer_range is supported, this function uses
+    \c glMapBufferRange instead of \c glMapBuffer.
+
+    \sa unmap(), create(), bind(), mapRange()
 */
 void *QOpenGLBuffer::map(QOpenGLBuffer::Access access)
 {
@@ -528,7 +544,48 @@ void *QOpenGLBuffer::map(QOpenGLBuffer::Access access)
 #endif
     if (!d->guard || !d->guard->id())
         return 0;
-    return d->funcs->glMapBuffer(d->type, access);
+    if (d->funcs->hasOpenGLExtension(QOpenGLExtensions::MapBufferRange)) {
+        QOpenGLBuffer::RangeAccessFlags rangeAccess = 0;
+        switch (access) {
+        case QOpenGLBuffer::ReadOnly:
+            rangeAccess = QOpenGLBuffer::RangeRead;
+            break;
+        case QOpenGLBuffer::WriteOnly:
+            rangeAccess = QOpenGLBuffer::RangeWrite;
+            break;
+        case QOpenGLBuffer::ReadWrite:
+            rangeAccess = QOpenGLBuffer::RangeRead | QOpenGLBuffer::RangeWrite;
+            break;
+        }
+        return d->funcs->glMapBufferRange(d->type, 0, size(), rangeAccess);
+    } else {
+        return d->funcs->glMapBuffer(d->type, access);
+    }
+}
+
+/*!
+    Maps the range specified by \a offset and \a count of the contents
+    of this buffer into the application's memory space and returns a
+    pointer to it.  Returns null if memory mapping is not possible.
+    The \a access parameter specifies a combination of access flags.
+
+    It is assumed that create() has been called on this buffer and that
+    it has been bound to the current context.
+
+    \note This function is not available on OpenGL ES 2.0 and earlier.
+
+    \sa unmap(), create(), bind()
+ */
+void *QOpenGLBuffer::mapRange(int offset, int count, QOpenGLBuffer::RangeAccessFlags access)
+{
+    Q_D(QOpenGLBuffer);
+#ifndef QT_NO_DEBUG
+    if (!isCreated())
+        qWarning("QOpenGLBuffer::mapRange(): buffer not created");
+#endif
+    if (!d->guard || !d->guard->id())
+        return 0;
+    return d->funcs->glMapBufferRange(d->type, offset, count, access);
 }
 
 /*!
@@ -539,8 +596,8 @@ void *QOpenGLBuffer::map(QOpenGLBuffer::Access access)
     It is assumed that this buffer has been bound to the current context,
     and that it was previously mapped with map().
 
-    This function is only supported under OpenGL/ES if the
-    \c{GL_OES_mapbuffer} extension is present.
+    \note This function is only supported under OpenGL ES 2.0 and
+    earlier if the \c{GL_OES_mapbuffer} extension is present.
 
     \sa map()
 */
diff --git a/src/gui/opengl/qopenglbuffer.h b/src/gui/opengl/qopenglbuffer.h
index ab564e9001..45e872e9a6 100644
--- a/src/gui/opengl/qopenglbuffer.h
+++ b/src/gui/opengl/qopenglbuffer.h
@@ -92,6 +92,17 @@ public:
         ReadWrite           = 0x88BA  // GL_READ_WRITE
     };
 
+    enum RangeAccessFlag
+    {
+        RangeRead             = 0x0001, // GL_MAP_READ_BIT
+        RangeWrite            = 0x0002, // GL_MAP_WRITE_BIT
+        RangeInvalidate       = 0x0004, // GL_MAP_INVALIDATE_RANGE_BIT
+        RangeInvalidateBuffer = 0x0008, // GL_MAP_INVALIDATE_BUFFER_BIT
+        RangeFlushExplicit    = 0x0010, // GL_MAP_FLUSH_EXPLICIT_BIT
+        RangeUnsynchronized   = 0x0020  // GL_MAP_UNSYNCHRONIZED_BIT
+    };
+    Q_DECLARE_FLAGS(RangeAccessFlags, RangeAccessFlag)
+
     QOpenGLBuffer::Type type() const;
 
     QOpenGLBuffer::UsagePattern usagePattern() const;
@@ -118,6 +129,7 @@ public:
     inline void allocate(int count) { allocate(0, count); }
 
     void *map(QOpenGLBuffer::Access access);
+    void *mapRange(int offset, int count, QOpenGLBuffer::RangeAccessFlags access);
     bool unmap();
 
 private:
@@ -126,6 +138,8 @@ private:
     Q_DECLARE_PRIVATE(QOpenGLBuffer)
 };
 
+Q_DECLARE_OPERATORS_FOR_FLAGS(QOpenGLBuffer::RangeAccessFlags)
+
 QT_END_NAMESPACE
 
 #endif // QT_NO_OPENGL
diff --git a/src/gui/opengl/qopenglextensions_p.h b/src/gui/opengl/qopenglextensions_p.h
index 065cbb0e57..907e315e41 100644
--- a/src/gui/opengl/qopenglextensions_p.h
+++ b/src/gui/opengl/qopenglextensions_p.h
@@ -99,7 +99,8 @@ public:
         Depth24                 = 0x00010000,
         SRGBFrameBuffer         = 0x00020000,
         MapBuffer               = 0x00040000,
-        GeometryShaders         = 0x00080000
+        GeometryShaders         = 0x00080000,
+        MapBufferRange          = 0x00100000
     };
     Q_DECLARE_FLAGS(OpenGLExtensions, OpenGLExtension)
 
@@ -107,6 +108,7 @@ public:
     bool hasOpenGLExtension(QOpenGLExtensions::OpenGLExtension extension) const;
 
     GLvoid *glMapBuffer(GLenum target, GLenum access);
+    GLvoid *glMapBufferRange(GLenum target, qopengl_GLintptr offset, qopengl_GLsizeiptr length, GLbitfield access);
     GLboolean glUnmapBuffer(GLenum target);
 
     void glBlitFramebuffer(GLint srcX0, GLint srcY0, GLint srcX1, GLint srcY1,
@@ -131,6 +133,8 @@ public:
     explicit QOpenGLExtensionsPrivate(QOpenGLContext *ctx);
 
     GLvoid* (QOPENGLF_APIENTRYP MapBuffer)(GLenum target, GLenum access);
+    GLvoid* (QOPENGLF_APIENTRYP MapBufferRange)(GLenum target, qopengl_GLintptr offset,
+                                                qopengl_GLsizeiptr length, GLbitfield access);
     GLboolean (QOPENGLF_APIENTRYP UnmapBuffer)(GLenum target);
     void (QOPENGLF_APIENTRYP BlitFramebuffer)(GLint srcX0, GLint srcY0, GLint srcX1, GLint srcY1,
                            GLint dstX0, GLint dstY0, GLint dstX1, GLint dstY1,
@@ -150,6 +154,16 @@ inline GLvoid *QOpenGLExtensions::glMapBuffer(GLenum target, GLenum access)
     return result;
 }
 
+inline GLvoid *QOpenGLExtensions::glMapBufferRange(GLenum target, qopengl_GLintptr offset,
+                                                   qopengl_GLsizeiptr length, GLbitfield access)
+{
+    Q_D(QOpenGLExtensions);
+    Q_ASSERT(QOpenGLExtensions::isInitialized(d));
+    GLvoid *result = d->MapBufferRange(target, offset, length, access);
+    Q_OPENGL_FUNCTIONS_DEBUG
+    return result;
+}
+
 inline GLboolean QOpenGLExtensions::glUnmapBuffer(GLenum target)
 {
     Q_D(QOpenGLExtensions);
diff --git a/src/gui/opengl/qopenglfunctions.cpp b/src/gui/opengl/qopenglfunctions.cpp
index 877cc6864d..43fff1c65a 100644
--- a/src/gui/opengl/qopenglfunctions.cpp
+++ b/src/gui/opengl/qopenglfunctions.cpp
@@ -388,7 +388,8 @@ static int qt_gl_resolve_extensions()
         if (format.majorVersion() >= 3)
             extensions |= QOpenGLExtensions::PackedDepthStencil
                 | QOpenGLExtensions::Depth24
-                | QOpenGLExtensions::ElementIndexUint;
+                | QOpenGLExtensions::ElementIndexUint
+                | QOpenGLExtensions::MapBufferRange;
 
         if (extensionMatcher.match("GL_OES_mapbuffer"))
             extensions |= QOpenGLExtensions::MapBuffer;
@@ -429,6 +430,8 @@ static int qt_gl_resolve_extensions()
             if (extensionMatcher.match("GL_EXT_packed_depth_stencil"))
                 extensions |= QOpenGLExtensions::PackedDepthStencil;
         }
+        if (extensionMatcher.match("GL_ARB_map_buffer_range"))
+            extensions |= QOpenGLExtensions::MapBufferRange;
     }
 
     if (format.renderableType() == QSurfaceFormat::OpenGL && format.version() >= qMakePair(3, 2))
@@ -3182,11 +3185,36 @@ static void QOPENGLF_APIENTRY qopenglfResolveVertexAttribPointer(GLuint indx, GL
 
 static GLvoid *QOPENGLF_APIENTRY qopenglfResolveMapBuffer(GLenum target, GLenum access)
 {
+#ifdef QT_OPENGL_ES_3
+    // It is possible that GL_OES_map_buffer is present, but then having to
+    // differentiate between glUnmapBufferOES and glUnmapBuffer causes extra
+    // headache. QOpenGLBuffer::map() will handle this automatically, while direct
+    // calls are better off with migrating to the standard glMapBufferRange.
+    if (QOpenGLContext::currentContext()->format().majorVersion() >= 3) {
+        qWarning("QOpenGLFunctions: glMapBuffer is not available in OpenGL ES 3.0 and up. Use glMapBufferRange instead.");
+        return 0;
+    } else
+#endif
     RESOLVE_FUNC(GLvoid *, ResolveOES, MapBuffer)(target, access);
 }
 
+static GLvoid *QOPENGLF_APIENTRY qopenglfResolveMapBufferRange(GLenum target, qopengl_GLintptr offset, qopengl_GLsizeiptr length, GLbitfield access)
+{
+#ifdef QT_OPENGL_ES_3
+    if (QOpenGLContext::currentContext()->format().majorVersion() >= 3)
+        return ::glMapBufferRange(target, offset, length, access);
+    else
+#endif
+    RESOLVE_FUNC(GLvoid *, 0, MapBufferRange)(target, offset, length, access);
+}
+
 static GLboolean QOPENGLF_APIENTRY qopenglfResolveUnmapBuffer(GLenum target)
 {
+#ifdef QT_OPENGL_ES_3
+    if (QOpenGLContext::currentContext()->format().majorVersion() >= 3)
+        return ::glUnmapBuffer(target);
+    else
+#endif
     RESOLVE_FUNC(GLboolean, ResolveOES, UnmapBuffer)(target);
 }
 
@@ -3455,6 +3483,7 @@ QOpenGLExtensionsPrivate::QOpenGLExtensionsPrivate(QOpenGLContext *ctx)
     : QOpenGLFunctionsPrivate(ctx)
 {
     MapBuffer = qopenglfResolveMapBuffer;
+    MapBufferRange = qopenglfResolveMapBufferRange;
     UnmapBuffer = qopenglfResolveUnmapBuffer;
     BlitFramebuffer = qopenglfResolveBlitFramebuffer;
     RenderbufferStorageMultisample = qopenglfResolveRenderbufferStorageMultisample;