// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only

#include <QtGui/qopengl.h>
#include <QtGui/private/qopenglcontext_p.h>
#include <QtCore/qatomic.h>
#include "qopenglbuffer.h"
#include <private/qopenglextensions_p.h>

#ifndef GL_CONTEXT_LOST
#define GL_CONTEXT_LOST                   0x0507
#endif

QT_BEGIN_NAMESPACE

/*!
    \class QOpenGLBuffer
    \brief The QOpenGLBuffer class provides functions for creating and managing OpenGL buffer objects.
    \since 5.0
    \ingroup painting-3D
    \inmodule QtOpenGL

    Buffer objects are created in the OpenGL server so that the
    client application can avoid uploading vertices, indices,
    texture image data, etc every time they are needed.

    QOpenGLBuffer objects can be copied around as a reference to the
    underlying OpenGL buffer object:

    \snippet code/src_gui_opengl_qopenglbuffer.cpp 0

    QOpenGLBuffer performs a shallow copy when objects are copied in this
    manner, but does not implement copy-on-write semantics.  The original
    object will be affected whenever the copy is modified.
*/

/*!
    \enum QOpenGLBuffer::Type
    This enum defines the type of OpenGL buffer object to create with QOpenGLBuffer.

    \value VertexBuffer Vertex buffer object for use when specifying
           vertex arrays.
    \value IndexBuffer Index buffer object for use with \c{glDrawElements()}.
    \value PixelPackBuffer Pixel pack buffer object for reading pixel
           data from the OpenGL server (for example, with \c{glReadPixels()}).
           Not supported under OpenGL/ES.
    \value PixelUnpackBuffer Pixel unpack buffer object for writing pixel
           data to the OpenGL server (for example, with \c{glTexImage2D()}).
           Not supported under OpenGL/ES.
*/

/*!
    \enum QOpenGLBuffer::UsagePattern
    This enum defines the usage pattern of a QOpenGLBuffer object.

    \value StreamDraw The data will be set once and used a few times
           for drawing operations.  Under OpenGL/ES 1.1 this is identical
           to StaticDraw.
    \value StreamRead The data will be set once and used a few times
           for reading data back from the OpenGL server.  Not supported
           under OpenGL/ES.
    \value StreamCopy The data will be set once and used a few times
           for reading data back from the OpenGL server for use in further
           drawing operations.  Not supported under OpenGL/ES.
    \value StaticDraw The data will be set once and used many times
           for drawing operations.
    \value StaticRead The data will be set once and used many times
           for reading data back from the OpenGL server.  Not supported
           under OpenGL/ES.
    \value StaticCopy The data will be set once and used many times
           for reading data back from the OpenGL server for use in further
           drawing operations.  Not supported under OpenGL/ES.
    \value DynamicDraw The data will be modified repeatedly and used
           many times for drawing operations.
    \value DynamicRead The data will be modified repeatedly and used
           many times for reading data back from the OpenGL server.
           Not supported under OpenGL/ES.
    \value DynamicCopy The data will be modified repeatedly and used
           many times for reading data back from the OpenGL server for
           use in further drawing operations.  Not supported under OpenGL/ES.
*/

/*!
    \enum QOpenGLBuffer::Access
    This enum defines the access mode for QOpenGLBuffer::map().

    \value ReadOnly The buffer will be mapped for reading only.
    \value WriteOnly The buffer will be mapped for writing only.
    \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:
    QOpenGLBufferPrivate(QOpenGLBuffer::Type t)
        : ref(1),
          type(t),
          guard(nullptr),
          usagePattern(QOpenGLBuffer::StaticDraw),
          actualUsagePattern(QOpenGLBuffer::StaticDraw),
          funcs(nullptr)
    {
    }

    QAtomicInt ref;
    QOpenGLBuffer::Type type;
    QOpenGLSharedResourceGuard *guard;
    QOpenGLBuffer::UsagePattern usagePattern;
    QOpenGLBuffer::UsagePattern actualUsagePattern;
    QOpenGLExtensions *funcs;
};

/*!
    Constructs a new buffer object of type QOpenGLBuffer::VertexBuffer.

    Note: this constructor just creates the QOpenGLBuffer instance.  The actual
    buffer object in the OpenGL server is not created until create() is called.

    \sa create()
*/
QOpenGLBuffer::QOpenGLBuffer()
    : d_ptr(new QOpenGLBufferPrivate(QOpenGLBuffer::VertexBuffer))
{
}

/*!
    Constructs a new buffer object of \a type.

    Note: this constructor just creates the QOpenGLBuffer instance.  The actual
    buffer object in the OpenGL server is not created until create() is called.

    \sa create()
*/
QOpenGLBuffer::QOpenGLBuffer(QOpenGLBuffer::Type type)
    : d_ptr(new QOpenGLBufferPrivate(type))
{
}

/*!
    Constructs a shallow copy of \a other.

    Note: QOpenGLBuffer does not implement copy-on-write semantics,
    so \a other will be affected whenever the copy is modified.
*/
QOpenGLBuffer::QOpenGLBuffer(const QOpenGLBuffer &other)
    : d_ptr(other.d_ptr)
{
    d_ptr->ref.ref();
}

/*!
    Destroys this buffer object, including the storage being
    used in the OpenGL server.
*/
QOpenGLBuffer::~QOpenGLBuffer()
{
    if (!d_ptr->ref.deref()) {
        destroy();
        delete d_ptr;
    }
}

/*!
    Assigns a shallow copy of \a other to this object.

    Note: QOpenGLBuffer does not implement copy-on-write semantics,
    so \a other will be affected whenever the copy is modified.
*/
QOpenGLBuffer &QOpenGLBuffer::operator=(const QOpenGLBuffer &other)
{
    if (d_ptr != other.d_ptr) {
        other.d_ptr->ref.ref();
        if (!d_ptr->ref.deref()) {
            destroy();
            delete d_ptr;
        }
        d_ptr = other.d_ptr;
    }
    return *this;
}

/*!
    Returns the type of buffer represented by this object.
*/
QOpenGLBuffer::Type QOpenGLBuffer::type() const
{
    Q_D(const QOpenGLBuffer);
    return d->type;
}

/*!
    Returns the usage pattern for this buffer object.
    The default value is StaticDraw.

    \sa setUsagePattern()
*/
QOpenGLBuffer::UsagePattern QOpenGLBuffer::usagePattern() const
{
    Q_D(const QOpenGLBuffer);
    return d->usagePattern;
}

/*!
    Sets the usage pattern for this buffer object to \a value.
    This function must be called before allocate() or write().

    \sa usagePattern(), allocate(), write()
*/
void QOpenGLBuffer::setUsagePattern(QOpenGLBuffer::UsagePattern value)
{
    Q_D(QOpenGLBuffer);
    d->usagePattern = d->actualUsagePattern = value;
}

namespace {
    void freeBufferFunc(QOpenGLFunctions *funcs, GLuint id)
    {
        funcs->glDeleteBuffers(1, &id);
    }
}

/*!
    Creates the buffer object in the OpenGL server.  Returns \c true if
    the object was created; false otherwise.

    This function must be called with a current QOpenGLContext.
    The buffer will be bound to and can only be used in
    that context (or any other context that is shared with it).

    This function will return false if the OpenGL implementation
    does not support buffers, or there is no current QOpenGLContext.

    \sa isCreated(), allocate(), write(), destroy()
*/
bool QOpenGLBuffer::create()
{
    Q_D(QOpenGLBuffer);
    if (d->guard && d->guard->id())
        return true;
    QOpenGLContext *ctx = QOpenGLContext::currentContext();
    if (ctx) {
        delete d->funcs;
        d->funcs = new QOpenGLExtensions(ctx);
        GLuint bufferId = 0;
        d->funcs->glGenBuffers(1, &bufferId);
        if (bufferId) {
            if (d->guard)
                d->guard->free();

            d->guard = new QOpenGLSharedResourceGuard(ctx, bufferId, freeBufferFunc);
            return true;
        }
    }
    return false;
}

/*!
    Returns \c true if this buffer has been created; false otherwise.

    \sa create(), destroy()
*/
bool QOpenGLBuffer::isCreated() const
{
    Q_D(const QOpenGLBuffer);
    return d->guard && d->guard->id();
}

/*!
    Destroys this buffer object, including the storage being
    used in the OpenGL server.  All references to the buffer will
    become invalid.
*/
void QOpenGLBuffer::destroy()
{
    Q_D(QOpenGLBuffer);
    if (d->guard) {
        d->guard->free();
        d->guard = nullptr;
    }
    delete d->funcs;
    d->funcs = nullptr;
}

/*!
    Reads the \a count bytes in this buffer starting at \a offset
    into \a data.  Returns \c true on success; false if reading from
    the buffer is not supported.  Buffer reading is not supported
    under OpenGL/ES.

    It is assumed that this buffer has been bound to the current context.

    \sa write(), bind()
*/
bool QOpenGLBuffer::read(int offset, void *data, int count)
{
#if !QT_CONFIG(opengles2)
    Q_D(QOpenGLBuffer);
    if (!d->funcs->hasOpenGLFeature(QOpenGLFunctions::Buffers) || !d->guard->id())
        return false;

    while (true) { // Clear error state.
        GLenum error = d->funcs->glGetError();
        if (error == GL_NO_ERROR)
            break;
        if (error == GL_CONTEXT_LOST)
            return false;
    };
    d->funcs->glGetBufferSubData(d->type, offset, count, data);
    return d->funcs->glGetError() == GL_NO_ERROR;
#else
    Q_UNUSED(offset);
    Q_UNUSED(data);
    Q_UNUSED(count);
    return false;
#endif
}

/*!
    Replaces the \a count bytes of this buffer starting at \a offset
    with the contents of \a data.  Any other bytes in the buffer
    will be left unmodified.

    It is assumed that create() has been called on this buffer and that
    it has been bound to the current context.

    \sa create(), read(), allocate()
*/
void QOpenGLBuffer::write(int offset, const void *data, int count)
{
#ifndef QT_NO_DEBUG
    if (!isCreated())
        qWarning("QOpenGLBuffer::write(): buffer not created");
#endif
    Q_D(QOpenGLBuffer);
    if (d->guard && d->guard->id())
        d->funcs->glBufferSubData(d->type, offset, count, data);
}

/*!
    Allocates \a count bytes of space to the buffer, initialized to
    the contents of \a data.  Any previous contents will be removed.

    It is assumed that create() has been called on this buffer and that
    it has been bound to the current context.

    \sa create(), read(), write()
*/
void QOpenGLBuffer::allocate(const void *data, int count)
{
#ifndef QT_NO_DEBUG
    if (!isCreated())
        qWarning("QOpenGLBuffer::allocate(): buffer not created");
#endif
    Q_D(QOpenGLBuffer);
    if (d->guard && d->guard->id())
        d->funcs->glBufferData(d->type, count, data, d->actualUsagePattern);
}

/*!
    \fn void QOpenGLBuffer::allocate(int count)
    \overload

    Allocates \a count bytes of space to the buffer.  Any previous
    contents will be removed.

    It is assumed that create() has been called on this buffer and that
    it has been bound to the current context.

    \sa create(), write()
*/

/*!
    Binds the buffer associated with this object to the current
    OpenGL context.  Returns \c false if binding was not possible, usually because
    type() is not supported on this OpenGL implementation.

    The buffer must be bound to the same QOpenGLContext current when create()
    was called, or to another QOpenGLContext that is sharing with it.
    Otherwise, false will be returned from this function.

    \sa release(), create()
*/
bool QOpenGLBuffer::bind()
{
#ifndef QT_NO_DEBUG
    if (!isCreated())
        qWarning("QOpenGLBuffer::bind(): buffer not created");
#endif
    Q_D(const QOpenGLBuffer);
    GLuint bufferId = d->guard ? d->guard->id() : 0;
    if (bufferId) {
        if (d->guard->group() != QOpenGLContextGroup::currentContextGroup()) {
#ifndef QT_NO_DEBUG
            qWarning("QOpenGLBuffer::bind: buffer is not valid in the current context");
#endif
            return false;
        }
        d->funcs->glBindBuffer(d->type, bufferId);
        return true;
    } else {
        return false;
    }
}

/*!
    Releases the buffer associated with this object from the
    current OpenGL context.

    This function must be called with the same QOpenGLContext current
    as when bind() was called on the buffer.

    \sa bind()
*/
void QOpenGLBuffer::release()
{
#ifndef QT_NO_DEBUG
    if (!isCreated())
        qWarning("QOpenGLBuffer::release(): buffer not created");
#endif
    Q_D(const QOpenGLBuffer);
    if (d->guard && d->guard->id())
        d->funcs->glBindBuffer(d->type, 0);
}

/*!
    Releases the buffer associated with \a type in the current
    QOpenGLContext.

    This function is a direct call to \c{glBindBuffer(type, 0)}
    for use when the caller does not know which QOpenGLBuffer has
    been bound to the context but wants to make sure that it
    is released.

    \snippet code/src_gui_opengl_qopenglbuffer.cpp 1
*/
void QOpenGLBuffer::release(QOpenGLBuffer::Type type)
{
    QOpenGLContext *ctx = QOpenGLContext::currentContext();
    if (ctx)
        ctx->functions()->glBindBuffer(GLenum(type), 0);
}

/*!
    Returns the OpenGL identifier associated with this buffer; zero if
    the buffer has not been created.

    \sa isCreated()
*/
GLuint QOpenGLBuffer::bufferId() const
{
    Q_D(const QOpenGLBuffer);
    return d->guard ? d->guard->id() : 0;
}

/*!
    Returns the size of the data in this buffer, for reading operations.
    Returns -1 if fetching the buffer size is not supported, or the
    buffer has not been created.

    It is assumed that this buffer has been bound to the current context.

    \sa isCreated(), bind()
*/
int QOpenGLBuffer::size() const
{
    Q_D(const QOpenGLBuffer);
    if (!d->guard || !d->guard->id())
        return -1;
    GLint value = -1;
    d->funcs->glGetBufferParameteriv(d->type, GL_BUFFER_SIZE, &value);
    return value;
}

/*!
    Maps 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 indicates the
    type of access to be performed.

    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 only supported under OpenGL ES 2.0 or
    earlier if the \c GL_OES_mapbuffer extension is present.

    \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)
{
    Q_D(QOpenGLBuffer);
#ifndef QT_NO_DEBUG
    if (!isCreated())
        qWarning("QOpenGLBuffer::map(): buffer not created");
#endif
    if (!d->guard || !d->guard->id())
        return nullptr;
    if (d->funcs->hasOpenGLExtension(QOpenGLExtensions::MapBufferRange)) {
        QOpenGLBuffer::RangeAccessFlags rangeAccess;
        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 nullptr;
    return d->funcs->glMapBufferRange(d->type, offset, count, access);
}

/*!
    Unmaps the buffer after it was mapped into the application's
    memory space with a previous call to map().  Returns \c true if
    the unmap succeeded; false otherwise.

    It is assumed that this buffer has been bound to the current context,
    and that it was previously mapped with map().

    \note This function is only supported under OpenGL ES 2.0 and
    earlier if the \c{GL_OES_mapbuffer} extension is present.

    \sa map()
*/
bool QOpenGLBuffer::unmap()
{
    Q_D(QOpenGLBuffer);
#ifndef QT_NO_DEBUG
    if (!isCreated())
        qWarning("QOpenGLBuffer::unmap(): buffer not created");
#endif
    if (!d->guard || !d->guard->id())
        return false;
    return d->funcs->glUnmapBuffer(d->type) == GL_TRUE;
}

QT_END_NAMESPACE
