Problem drawing triangles with QSGGeometryNode (Scene Graph).

lswa · wrote on 20 Dec 2016, 05:38

Hello, I have problem with topic. I extend customgeometry example from Qt Docs (http://doc.qt.io/qt-5/qtquick-scenegraph-customgeometry-example.html) and try to draw sequence of triangles. Bellow my code:

main.cpp:

#include <QGuiApplication>
#include <QQmlApplicationEngine>

#include "TestOpenGL.h"

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

    qmlRegisterType<TestOpenGL>("TestModule", 1, 0, "TestOpenGL");

    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

    return app.exec();
}

TestOpenGL.h:

#ifndef TESTOPENGL_H
#define TESTOPENGL_H

#include <QQuickItem>

class QSGGeometryNode;

class TestOpenGL : public QQuickItem
{
    Q_OBJECT
    Q_PROPERTY(QColor color READ color WRITE setColor NOTIFY colorChanged)
    Q_PROPERTY(QList<qreal> vertices READ vertices WRITE setVertices NOTIFY verticesChanged)

public:
    explicit TestOpenGL(QQuickItem *parent = 0);

    QColor color();
    void setColor(const QColor &color);

    QList<qreal> &vertices();
    void setVertices(const QList<qreal>& newVal);

signals:
    void colorChanged();
    void verticesChanged();

protected:
    QSGNode *updatePaintNode(QSGNode *, UpdatePaintNodeData *);
    QSGGeometryNode *drawBorder();

protected:
    QColor          m_color;
    QList<qreal>    m_vertices;
};

#endif // TESTOPENGL_H

TestOpenGL.cpp:

#include "TestOpenGL.h"

#include <QtMath>
#include <QSGNode>
#include <QSGVertexColorMaterial>

TestOpenGL::TestOpenGL(QQuickItem *parent)
    : QQuickItem(parent)
    , m_color(0, 0, 0, 0)
{
    setFlag(ItemHasContents, true);
}

QColor TestOpenGL::color()
{
    return m_color;
}

void TestOpenGL::setColor(const QColor &color)
{
    m_color = color;
    update();
    emit colorChanged();
}

QList<qreal> &TestOpenGL::vertices()
{
    return m_vertices;
}

void TestOpenGL::setVertices(const QList<qreal>& newVal)
{
    m_vertices = newVal;
    update();
    emit verticesChanged();
}

QSGNode *TestOpenGL::updatePaintNode(QSGNode *oldNode, UpdatePaintNodeData *)
{
    QSGNode *pNode = 0;

    if (!oldNode) {
        pNode = drawBorder();
    }
    pNode->markDirty(QSGNode::DirtyGeometry);

    return pNode;
}

QSGGeometryNode *TestOpenGL::drawBorder()
{
    QSGGeometryNode *ret = new QSGGeometryNode();
    QSGGeometry *geometry;
    QSGVertexColorMaterial *material = new QSGVertexColorMaterial;
    geometry = new QSGGeometry(QSGGeometry::defaultAttributes_ColoredPoint2D(), 0);

    ret->setMaterial(material);
    ret->setFlag(QSGNode::OwnsMaterial);

    ret->setGeometry(geometry);
//    ret->setFlag(QSGNode::OwnsGeometry);

    geometry->setDrawingMode(GL_TRIANGLE_STRIP);
    int vertexStride = geometry->sizeOfVertex();

    int innerVertexCount = m_vertices.size() / 2;
    int vertexCount = innerVertexCount;
//    int vertexCount = innerVertexCount * 3;
//    int vertexCount = innerVertexCount * 6;

    int fillIndexCount = innerVertexCount;
    int indexCount = innerVertexCount;

    geometry->allocate(vertexCount, indexCount);
    QSGGeometry::ColoredPoint2D* vertices = geometry->vertexDataAsColoredPoint2D();
    memset(vertices, 0, vertexCount * vertexStride);
    quint16 *indices = geometry->indexDataAsUShort();

    for (int i = 0; i < fillIndexCount; ++i)
    {
        vertices[i].set(m_vertices[i * 2], m_vertices[i * 2 + 1], 255, 0, 0, 255);
        indices[i * 2] = i * 2;
        indices[i * 2 + 1] = i * 2 + 1;
    }

    return ret;
}

main.qml:

import QtQuick 2.5
import QtQuick.Window 2.2
import TestModule 1.0

Window {
    visible: true
    width: 640
    height: 480
    title: qsTr("Test OpenGL")

    MouseArea {
        anchors.fill: parent
        onClicked: {
            Qt.quit();
        }
    }

    TestOpenGL {
        anchors.fill: parent
        vertices: [
            0, 0
            , 0, 100
            , 50, 0
            , 50, 100       //working with int vertexCount = innerVertexCount. On exit no warning only "The program has unexpectedly finished." message
//            , 100, 0        //working with int vertexCount = innerVertexCount but show warnings when application stopped
//            , 100, 100      //working with int vertexCount = innerVertexCount but show warnings when application stopped
//            , 150, 0        //working with int vertexCount = innerVertexCount * 3
//            , 150, 100      //not working
        ]
    }
}

Problem here: I can't draw more than few triangles. And I can't understand where is an error. E.g. if use vertices property with 8 vertices - exceptrion occur in qlist.cpp (realloc_grow(int growth): 153):

Debugging starts
QML debugging is enabled. Only use this in a safe environment.
Qt: gdb: -nograb added to command-line options.
	 Use the -dograb option to enforce grabbing.
QML Debugger: Waiting for connection on port 41807...
*** Error in `/home/leon/Documents/progs/qt/test_apps/build-TestOpenGL-Manual_Qt_5_7_0_gcc_64-Debug/TestOpenGL': realloc(): invalid next size: 0x00007fffd011f670 ***
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(+0x777e5)[0x7ffff5bce7e5]
/lib/x86_64-linux-gnu/libc.so.6(+0x82a5a)[0x7ffff5bd9a5a]
/lib/x86_64-linux-gnu/libc.so.6(realloc+0x179)[0x7ffff5bdac89]
/home/leon/src/qt5/5.7.0/gcc_64/lib/libQt5Core.so.5(_ZN9QListData12realloc_growEi+0x8f)[0x7ffff6618c19]
/home/leon/src/qt5/5.7.0/gcc_64/lib/libQt5Core.so.5(_ZN9QListData6appendEi+0xff)[0x7ffff6618da3]
/home/leon/src/qt5/5.7.0/gcc_64/lib/libQt5Core.so.5(_ZN9QListData6appendEv+0x1d)[0x7ffff6618deb]
/home/leon/src/qt5/5.7.0/gcc_64/lib/libQt5Quick.so.5(+0x24cc2a)[0x7ffff7a5dc2a]
/home/leon/src/qt5/5.7.0/gcc_64/lib/libQt5Quick.so.5(+0x24e179)[0x7ffff7a5f179]
/home/leon/src/qt5/5.7.0/gcc_64/lib/libQt5Quick.so.5(_ZN19QQuickWindowPrivate15updateDirtyNodeEP10QQuickItem+0x122e)[0x7ffff7a58d32]
/home/leon/src/qt5/5.7.0/gcc_64/lib/libQt5Quick.so.5(_ZN19QQuickWindowPrivate16updateDirtyNodesEv+0x290)[0x7ffff7a57712]
/home/leon/src/qt5/5.7.0/gcc_64/lib/libQt5Quick.so.5(_ZN19QQuickWindowPrivate14syncSceneGraphEv+0x143)[0x7ffff7a4a93f]
/home/leon/src/qt5/5.7.0/gcc_64/lib/libQt5Quick.so.5(+0x1fafaf)[0x7ffff7a0bfaf]
/home/leon/src/qt5/5.7.0/gcc_64/lib/libQt5Quick.so.5(+0x1fb4a7)[0x7ffff7a0c4a7]
/home/leon/src/qt5/5.7.0/gcc_64/lib/libQt5Quick.so.5(+0x1fc197)[0x7ffff7a0d197]
/home/leon/src/qt5/5.7.0/gcc_64/lib/libQt5Core.so.5(+0xc61fa)[0x7ffff657e1fa]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x76ba)[0x7ffff54596ba]
/lib/x86_64-linux-gnu/libc.so.6(clone+0x6d)[0x7ffff5c5d82d]
.
.
.

Please help me
My platform: Ubuntu 16.04 64bit, Qt 5.7.0.
On my Windows 10 application works only with FTH enabled. I got message: FTH: *** Fault tolerant heap shim applied to current process. This is usually due to previous crashes. *** So I conclude that problem presented on Windows 10 too.

lswa · wrote on 21 Dec 2016, 00:55

I found a reason. Wrong is 2 lines from TestOpenGL.cpp file, need replace them with only one line:

        indices[i] = i;
//        indices[i * 2] = i * 2;
//        indices[i * 2 + 1] = i * 2 + 1;