qcustemplot使用opengl加速

网上有很多讲qCustomPlot启动OpenGL的文章，有些是很有用的，但也好像没有完全说清楚，现在把我觉得有用的收集起来，并加上一些自己的理解。

1. 下载qCustomPlot

   https://www.qcustomplot.com/

2. 下载freeglut库

   由于qCustomPlot需要调用glut库里的函数，但是glut库比较老旧，而且在实际测试中，也发现一旦new了多个图表控件，当鼠标在几个窗口之间点击的时候，会互相影响，错乱，甚至崩溃的现象。freeglut库是glut的最佳替代版本，更换之后，果然解决了这个问题。

   http://freeglut.sourceforge.net/index.php
   我使用的是qt的mingw编译器，所以参考下面的文档
   https://www.transmissionzero.co.uk/computing/using-glut-with-mingw/

3. 将"qcustomplot.h和qcustomplot.cpp"添加到自己的工程中，在qcustomplot.cpp最前面加一条头文件引用

	#include "qcustomplot.h"
	#include 
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4. 在qcustomplot.cpp文件中搜索 “QCPPaintBufferGlFbo::draw”，在“drawImage”之前一行加入如下代码以修复上下文错误

/* inherits documentation from base class */
void QCPPaintBufferGlFbo::draw(QCPPainter *painter) const
{
  if (!painter || !painter->isActive())
  {
    qDebug() << Q_FUNC_INFO << "invalid or inactive painter passed";
    return;
  }
  if (!mGlFrameBuffer)
  {
    qDebug() << Q_FUNC_INFO << "OpenGL frame buffer object doesn't exist, reallocateBuffer was not called?";
    return;
  }
 //增加下面的代码
  if (QOpenGLContext::currentContext() != mGlContext.data()) {
        mGlContext.data()->makeCurrent(mGlContext.data()->surface());
  }
 
  painter->drawImage(0, 0, mGlFrameBuffer->toImage());
}
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如果不加该行代码，运行会显示下面的问题。

QOpenGLFramebufferObject::bind() called from incompatible context
QOpenGLFramebufferObject::bind() called from incompatible context
QOpenGLFramebufferObject::bind() called from incompatible context
QOpenGLFramebufferObject::bind() called from incompatible context
QOpenGLFramebufferObject::bind() called from incompatible context
QOpenGLFramebufferObject::bind() called from incompatible context
QOpenGLFramebufferObject::bind() called from incompatible context
QOpenGLFramebufferObject::bind() called from incompatible context
QOpenGLFramebufferObject::bind() called from incompatible context
QOpenGLFramebufferObject::bind() called from incompatible context
QOpenGLFramebufferObject::bind() called from incompatible context
QOpenGLFramebufferObject::bind() called from incompatible context
QOpenGLFramebufferObject::bind() called from incompatible context
QOpenGLFramebufferObject::bind() called from incompatible context
QOpenGLFramebufferObject::bind() called from incompatible context
QOpenGLFramebufferObject::bind() called from incompatible context
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5. 在工程.pro中添加以下内容:

    在工程右键"添加库"，找到libfreeglut.a库文件和头文件
    **把freeglut.dll文件拷贝到exe所在目录下**，注意32位和64位库的目录有区别。
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在库引用目录中添加 -lopengl32 -lglu32 否则会报如下的错误。

debug/qcustomplot.o: In function `ZN19QCPPaintBufferGlFbo5clearERK6QColor':
F:\mrzhang\Works\RecordWave\build-QtRecordWave-Desktop_Qt_5_12_4_MinGW_32_bit-Debug/../QtRecordWave/qcustomplot.cpp:937: undefined reference to `_imp__glClearColor@16'
F:\mrzhang\Works\RecordWave\build-QtRecordWave-Desktop_Qt_5_12_4_MinGW_32_bit-Debug/../QtRecordWave/qcustomplot.cpp:938: undefined reference to `_imp__glClear@4'
collect2.exe: error: ld returned 1 exit status
mingw32-make[1]: *** [Makefile.Debug:105: debug/QtRecordWave.exe] Error 1
mingw32-make: *** [Makefile:38: debug] Error 2
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贴下我的pro文件。
注意下面的中文注释

#-------------------------------------------------
#
# Project created by QtCreator 2022-10-15T09:59:54
#
#-------------------------------------------------

QT       += core gui network opengl
#添加 opengl
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets printsupport

TARGET = QtRecordWave
TEMPLATE = app

# The following define makes your compiler emit warnings if you use
# any feature of Qt which has been marked as deprecated (the exact warnings
# depend on your compiler). Please consult the documentation of the
# deprecated API in order to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS QCUSTOMPLOT_USE_OPENGL
#添加QCUSTOMPLOT_USE_OPENGL
# You can also make your code fail to compile if you use deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

CONFIG += c++11

SOURCES += \
        dialog.cpp \
        main.cpp \
        mainwindow.cpp \
        procthread.cpp \
        qcustomplot.cpp \
        tcpserver.cpp \
        tcpsocket.cpp \
        waveplot.cpp

HEADERS += \
        dialog.h \
        mainwindow.h \
        procthread.h \
        qcustomplot.h \
        tcpserver.h \
        tcpsocket.h \
        waveplot.h

FORMS += \
        dialog.ui \
        mainwindow.ui

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

win32:LIBS += -L$$PWD/freeglut-MinGW-3.0.0-1.mp/freeglut/lib/ -lfreeglut -lopengl32 -lglu32
else:unix: LIBS += -L$$PWD/freeglut-MinGW-3.0.0-1.mp/freeglut/lib/ -lfreeglut -lopengl32 -lglu32

INCLUDEPATH += $$PWD/freeglut-MinGW-3.0.0-1.mp/freeglut/include
DEPENDPATH += $$PWD/freeglut-MinGW-3.0.0-1.mp/freeglut/include

INCLUDEPATH += $$PWD/freeglut-MinGW-3.0.0-1.mp/freeglut/include
DEPENDPATH += $$PWD/freeglut-MinGW-3.0.0-1.mp/freeglut/include
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6. 在你代码中设置qCustomPlot开启OpenGl功能，在运行时，看到“应用程序输出”窗口有opengl = true字样，说明启动成功。

ui->customPlot->setOpenGl(true);
qDebug()<<“opengle=”openGl();

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