- Qt 5.5
- Qt OpenGL
- Textures Example
- glwidget.cpp Example File
- Qt 5.5.1 Reference Documentation

# glwidget.cpp Example File

textures/glwidget.cpp

    /****************************************************************************
    **
    ** Copyright (C) 2015 The Qt Company Ltd.
    ** Contact: http://www.qt.io/licensing/
    **
    ** This file is part of the examples of the Qt Toolkit.
    **
    ** $QT_BEGIN_LICENSE:BSD$
    ** You may use this file under the terms of the BSD license as follows:
    **
    ** "Redistribution and use in source and binary forms, with or without
    ** modification, are permitted provided that the following conditions are
    ** met:
    **   * Redistributions of source code must retain the above copyright
    **     notice, this list of conditions and the following disclaimer.
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    **     notice, this list of conditions and the following disclaimer in
    **     the documentation and/or other materials provided with the
    **     distribution.
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    **     contributors may be used to endorse or promote products derived
    **     from this software without specific prior written permission.
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    ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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    #include "glwidget.h"
    #include <QOpenGLShaderProgram>
    #include <QOpenGLTexture>
    #include <QMouseEvent>

    GLWidget::GLWidget(QWidget *parent)
        : QOpenGLWidget(parent),
          clearColor(Qt::black),
          xRot(0),
          yRot(0),
          zRot(0),
          program(0)
    {
        memset(textures, 0, sizeof(textures));
    }

    GLWidget::~GLWidget()
    {
        makeCurrent();
        vbo.destroy();
        for (int i = 0; i < 6; ++i)
            delete textures[i];
        delete program;
        doneCurrent();
    }

    QSize GLWidget::minimumSizeHint() const
    {
        return QSize(50, 50);
    }

    QSize GLWidget::sizeHint() const
    {
        return QSize(200, 200);
    }

    void GLWidget::rotateBy(int xAngle, int yAngle, int zAngle)
    {
        xRot += xAngle;
        yRot += yAngle;
        zRot += zAngle;
        update();
    }

    void GLWidget::setClearColor(const QColor &color)
    {
        clearColor = color;
        update();
    }

    void GLWidget::initializeGL()
    {
        initializeOpenGLFunctions();

        makeObject();

        glEnable(GL_DEPTH_TEST);
        glEnable(GL_CULL_FACE);

    #define PROGRAM_VERTEX_ATTRIBUTE 0
    #define PROGRAM_TEXCOORD_ATTRIBUTE 1

        QOpenGLShader *vshader = new QOpenGLShader(QOpenGLShader::Vertex, this);
        const char *vsrc =
            "attribute highp vec4 vertex;\n"
            "attribute mediump vec4 texCoord;\n"
            "varying mediump vec4 texc;\n"
            "uniform mediump mat4 matrix;\n"
            "void main(void)\n"
            "{\n"
            "    gl_Position = matrix * vertex;\n"
            "    texc = texCoord;\n"
            "}\n";
        vshader->compileSourceCode(vsrc);

        QOpenGLShader *fshader = new QOpenGLShader(QOpenGLShader::Fragment, this);
        const char *fsrc =
            "uniform sampler2D texture;\n"
            "varying mediump vec4 texc;\n"
            "void main(void)\n"
            "{\n"
            "    gl_FragColor = texture2D(texture, texc.st);\n"
            "}\n";
        fshader->compileSourceCode(fsrc);

        program = new QOpenGLShaderProgram;
        program->addShader(vshader);
        program->addShader(fshader);
        program->bindAttributeLocation("vertex", PROGRAM_VERTEX_ATTRIBUTE);
        program->bindAttributeLocation("texCoord", PROGRAM_TEXCOORD_ATTRIBUTE);
        program->link();

        program->bind();
        program->setUniformValue("texture", 0);
    }

    void GLWidget::paintGL()
    {
        glClearColor(clearColor.redF(), clearColor.greenF(), clearColor.blueF(), clearColor.alphaF());
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        QMatrix4x4 m;
        m.ortho(-0.5f, +0.5f, +0.5f, -0.5f, 4.0f, 15.0f);
        m.translate(0.0f, 0.0f, -10.0f);
        m.rotate(xRot / 16.0f, 1.0f, 0.0f, 0.0f);
        m.rotate(yRot / 16.0f, 0.0f, 1.0f, 0.0f);
        m.rotate(zRot / 16.0f, 0.0f, 0.0f, 1.0f);

        program->setUniformValue("matrix", m);
        program->enableAttributeArray(PROGRAM_VERTEX_ATTRIBUTE);
        program->enableAttributeArray(PROGRAM_TEXCOORD_ATTRIBUTE);
        program->setAttributeBuffer(PROGRAM_VERTEX_ATTRIBUTE, GL_FLOAT, 0, 3, 5 * sizeof(GLfloat));
        program->setAttributeBuffer(PROGRAM_TEXCOORD_ATTRIBUTE, GL_FLOAT, 3 * sizeof(GLfloat), 2, 5 * sizeof(GLfloat));

        for (int i = 0; i < 6; ++i) {
            textures[i]->bind();
            glDrawArrays(GL_TRIANGLE_FAN, i * 4, 4);
        }
    }
    void GLWidget::resizeGL(int width, int height)
    {
        int side = qMin(width, height);
        glViewport((width - side) / 2, (height - side) / 2, side, side);
    }

    void GLWidget::mousePressEvent(QMouseEvent *event)
    {
        lastPos = event->pos();
    }

    void GLWidget::mouseMoveEvent(QMouseEvent *event)
    {
        int dx = event->x() - lastPos.x();
        int dy = event->y() - lastPos.y();

        if (event->buttons() & Qt::LeftButton) {
            rotateBy(8 * dy, 8 * dx, 0);
        } else if (event->buttons() & Qt::RightButton) {
            rotateBy(8 * dy, 0, 8 * dx);
        }
        lastPos = event->pos();
    }

    void GLWidget::mouseReleaseEvent(QMouseEvent * /* event */)
    {
        emit clicked();
    }

    void GLWidget::makeObject()
    {
        static const int coords[6][4][3] = {
            { { +1, -1, -1 }, { -1, -1, -1 }, { -1, +1, -1 }, { +1, +1, -1 } },
            { { +1, +1, -1 }, { -1, +1, -1 }, { -1, +1, +1 }, { +1, +1, +1 } },
            { { +1, -1, +1 }, { +1, -1, -1 }, { +1, +1, -1 }, { +1, +1, +1 } },
            { { -1, -1, -1 }, { -1, -1, +1 }, { -1, +1, +1 }, { -1, +1, -1 } },
            { { +1, -1, +1 }, { -1, -1, +1 }, { -1, -1, -1 }, { +1, -1, -1 } },
            { { -1, -1, +1 }, { +1, -1, +1 }, { +1, +1, +1 }, { -1, +1, +1 } }
        };

        for (int j = 0; j < 6; ++j)
            textures[j] = new QOpenGLTexture(QImage(QString(":/images/side%1.png").arg(j + 1)).mirrored());

        QVector<GLfloat> vertData;
        for (int i = 0; i < 6; ++i) {
            for (int j = 0; j < 4; ++j) {
                // vertex position
                vertData.append(0.2 * coords[i][j][0]);
                vertData.append(0.2 * coords[i][j][1]);
                vertData.append(0.2 * coords[i][j][2]);
                // texture coordinate
                vertData.append(j == 0 || j == 3);
                vertData.append(j == 0 || j == 1);
            }
        }

        vbo.create();
        vbo.bind();
        vbo.allocate(vertData.constData(), vertData.count() * sizeof(GLfloat));
    }