OpenGL Window Example

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#include "openglwindow.h"

#include <QtGui/QGuiApplication>
#include <QtGui/QMatrix4x4>
#include <QtGui/QOpenGLShaderProgram>
#include <QtGui/QScreen>

#include <QtCore/qmath.h>

class TriangleWindow : public OpenGLWindow
{
public:
    TriangleWindow();

    void initialize() override;
    void render() override;

private:
    GLuint m_posAttr;
    GLuint m_colAttr;
    GLuint m_matrixUniform;

    QOpenGLShaderProgram *m_program;
    int m_frame;
};

TriangleWindow::TriangleWindow()
    : m_program(0)
    , m_frame(0)
{
}

int main(int argc, char **argv)
{
    QGuiApplication app(argc, argv);

    QSurfaceFormat format;
    format.setSamples(16);

    TriangleWindow window;
    window.setFormat(format);
    window.resize(640, 480);
    window.show();

    window.setAnimating(true);

    return app.exec();
}

static const char *vertexShaderSource =
    "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 =
    "varying lowp vec4 col;\n"
    "void main() {\n"
    "   gl_FragColor = col;\n"
    "}\n";

void TriangleWindow::initialize()
{
    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 TriangleWindow::render()
{
    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();

    ++m_frame;
}