QtOpenGL示例openglwindow

基於qt5.7.1示例程式openglwindow的解讀1

• 程式流程

    show()-->exposeEvent()-->run()-->postEvent()
    -->event()-->run()-->postEvent()
    -->event()-->run()-->postEvent()
    -->event()-->run()-->postEvent()
    -->event()-->run()-->postEvent()
 


    註釋： 每次視窗大小改變是都會產生exposeEvent訊號，
          繪畫結束後通過postEvent產生一個event訊號。

• pro檔案

QT -= core
QT += gui

CONFIG += c++11
CONFIG += console

SOURCES += main.cpp \
    openglwindow.cpp

HEADERS += \
    openglwindowain.cpp

• main.cpp檔案

#include "openglwindow.h"
#include <QtGui/QGuiApplication>
 


int main(int argc, char *argv[])
{
    QGuiApplication a(argc, argv);

    OpenGLWindow window;
    window.resize(640, 480);
    window.show();
    // window.run();      // 不需要run,show()自動進入
    return a.exec()
}

• openglwindow.h檔案

#ifndef OPENGLWINDOW_H
#define OPENGLWINDOW_H

#include <QtGui/QWindow>
 

#include <QtGui/QOpenGLFunctions>

QT_BEGIN_NAMESPACE
class QPainter;
class QOpenGLContext;
class QOpenGLPaintDevice;
class QOpenGLShaderProgram;
QT_END_NAMESPACE

class OpenGLWindow : public QWindow, protected QOpenGLFunctions
{
    Q_OBJECT
public:
    explicit OpenGLWindow(QWindow *parent = 0);
     ~OpenGLWindow();
      void TestFunction();                  // Test繪圖
      void InitShader();                    // 初始化著色器(畫刷)
      void DrawImage();                     // 執行繪圖動作
private:
    QOpenGLContext *m_context;              // 畫板物件
    QOpenGLShaderProgram *m_program;        // 著色器(畫刷)物件

    GLuint m_posAttr;                       // 著色器引數：屬性
    GLuint m_colAttr;                       // 著色器引數：紋理
    GLuint m_matrixUniform;                 // 著色器引數：uniform

    int  m_frame;                           // 迴圈變數，只要到一次
    bool m_update_pending;                  // 繪圖完成標誌(視窗更新標誌)

public slots:
    void run();                             // 動畫效果實現

protected:                                  // 訊息發生器(過載而來)
    bool event(QEvent *event) Q_DECL_OVERRIDE;
    void exposeEvent(QExposeEvent *event) Q_DECL_OVERRIDE;
};

#endif // OPENGLWINDOW_H

• openglwindow.cpp檔案

#include "openglwindow.h"
#include <QtCore/QCoreApplication>
#include <QtGui/QOpenGLShaderProgram>
#include <QtGui/QOpenGLContext>
#include <QtGui/QScreen>

static const char *vertexShaderSource =     // 著色器語言
    "attribute highp vec4 posAttr;\n"
    "attribute lowp vec4 colAttr;\n"
    "varying lowp vec4 col;\n"
    "uniform highp mat4 matrix;\n"
    "void main() {\n"
    "   col = colAttr;\n"
    "   gl_Position = matrix * posAttr;\n"
    "}\n";

static const char *fragmentShaderSource =   // 著色器語言
    "varying lowp vec4 col;\n"
    "void main() {\n"
    "   gl_FragColor = col;\n"
    "}\n";

OpenGLWindow::OpenGLWindow(QWindow *parent)
    : QWindow(parent)
    , m_context(0)
    , m_frame(0)
    , m_update_pending(false)
{
    setSurfaceType(QWindow::OpenGLSurface);
}

OpenGLWindow::~OpenGLWindow()
{
    if(m_context)
     delete m_context;
}

void OpenGLWindow::TestFunction()
{
    if(m_context)
    {
        m_context->makeCurrent(this);
        DrawImage();
        m_context->swapBuffers(this);
        return;
    }

    m_context = new QOpenGLContext(this);
    m_context->create();

    m_context->makeCurrent(this);
    initializeOpenGLFunctions();
    InitShader();
    DrawImage();
    m_context->swapBuffers(this);
}

void OpenGLWindow::InitShader()
{
    m_program = new QOpenGLShaderProgram(this);
    m_program->addShaderFromSourceCode(QOpenGLShader::Vertex, vertexShaderSource);
    m_program->addShaderFromSourceCode(QOpenGLShader::Fragment, fragmentShaderSource);
    m_program->link();
    m_posAttr = m_program->attributeLocation("posAttr");
    m_colAttr = m_program->attributeLocation("colAttr");
    m_matrixUniform = m_program->uniformLocation("matrix");
}

void OpenGLWindow::DrawImage()
{
    const qreal retinaScale = devicePixelRatio();
    glViewport(0, 0, width() * retinaScale, height() * retinaScale);
    glClear(GL_COLOR_BUFFER_BIT);
    m_program->bind();

    QMatrix4x4 matrix;
    matrix.perspective(60.0f, 4.0f/3.0f, 0.1f, 100.0f);
    matrix.translate(0, 0, -2);
    matrix.rotate(100.0f * m_frame++ / screen()->refreshRate(), 0, 1, 0); 

    m_program->setUniformValue(m_matrixUniform, matrix);

    GLfloat vertices[] = {
        0.0f, 0.707f,
        -0.5f, -0.5f,
        0.5f, -0.5f
    };

    GLfloat colors[] = {
        1.0f, 0.0f, 0.0f,
        0.0f, 1.0f, 0.0f,
        0.0f, 0.0f, 1.0f
    };

    glVertexAttribPointer(m_posAttr, 2, GL_FLOAT, GL_FALSE, 0, vertices);
    glVertexAttribPointer(m_colAttr, 3, GL_FLOAT, GL_FALSE, 0, colors);

    glEnableVertexAttribArray(0);
    glEnableVertexAttribArray(1);

    glDrawArrays(GL_TRIANGLES, 0, 3);

    glDisableVertexAttribArray(1);
    glDisableVertexAttribArray(0);

    m_program->release();
}

bool OpenGLWindow::event(QEvent *event)
{
    if(event->type() != QEvent::UpdateRequest)
        return QWindow::event(event);

    m_update_pending = false;
    if(isExposed()) run();

    return true;
}

void OpenGLWindow::exposeEvent(QExposeEvent *event)
{
    Q_UNUSED(event);

    if(isExposed()) run();
}

void OpenGLWindow::run()
{
    TestFunction();

    if (m_update_pending) return;
    m_update_pending = true;

    QCoreApplication::postEvent(this, new QEvent(QEvent::UpdateRequest));
}

• 參考網頁：