我正在尝试制作一个应用程序,您可以在其中用手指在 Canvas 上绘图。
为此,我继承了 QWidget
作为MFCanvas
, 在 QML 中注册类
qmlRegisterType<>()
, 实现虚拟 paintEvent();
功能,和
用 QPainter
在上面绘图在paintEvent();
里面功能。
问题:
施工后,QPainter
抛出此警告:
QWidget::paintEngine: Should no longer be called
然后,抛出一些其他相关警告:
QPainter::begin: Paint device returned engine == 0, type: 1
QPainter::setPen: Painter not active
难怪:QPainter
什么都没画...
另外,我应该调用paintEvent();
吗?一个人?
或者它应该由 QWidget
调用每一帧吗? ,我不知何故搞砸了?
我在网上搜索过,但我找到的所有帖子都没有答案,或者它们在哪里
使用 QWidget
以外的东西.
我的代码:
mfcanvas.cpp:
#include "mfcanvas.h"
#include <QDebug>
#include <QPainter>
#include <QVector2D>
#include <QList>
MFCanvas::MFCanvas(QWidget *parent) : QWidget(parent)
{
paths = new QList<QList<QVector2D>*>();
current = NULL;
QWidget::resize(100, 100);
}
MFCanvas::~MFCanvas()
{
delete paths;
}
void MFCanvas::paintEvent(QPaintEvent *)
{
if(current!=NULL){
if(current->length() > 1){
QPainter painter(this);
painter.setPen(Qt::black);
for(int i = 1; i < current->length(); i++){
painter.drawLine(current->at(i-1).x(), current->at(i-1).y(), current->at(i).x(), current->at(i).y());
}
}
}
}
void MFCanvas::pressed(float x, float y)
{
if(current==NULL){
qDebug() << "null:"<<current;
current = new QList<QVector2D>();
current->append(QVector2D(x, y));
}else{
qDebug() << "current:"<<current;
}
paintEvent(NULL);
}
void MFCanvas::update(float x, float y)
{
current->append(QVector2D(x, y));
}
void MFCanvas::resize(int w, int h)
{
QWidget::resize(w, h);
}
主要.cpp:
#include <QApplication>
#include <QQmlApplicationEngine>
#include <QtQml>
#include <QSurfaceFormat>
#include "creator.h"
#include "mfcanvas.h"
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
qmlRegisterType<MFCanvas>("com.cpp.mfcanvas", 1, 0, "MFCanvas");
QQmlApplicationEngine engine;
QQmlComponent *component = new QQmlComponent(&engine);
QObject::connect(&engine, SIGNAL(quit()), QCoreApplication::instance(), SLOT(quit()));
Creator creator(component);
QObject::connect(component, SIGNAL(statusChanged(QQmlComponent::Status)), &creator, SLOT(create(QQmlComponent::Status)));
component->loadUrl(QUrl("qrc:///main.qml"));
int rv;
rv = app.exec();
delete component;
return rv;
}
创建者.cpp:
#include "creator.h"
#include <QQuickWindow>
#include <QDebug>
Creator::Creator(QQmlComponent *component)
{
this->component = component;
}
void Creator::create(QQmlComponent::Status status)
{
if(status == QQmlComponent::Ready){
QObject *topLevel = component->create();
QQuickWindow::setDefaultAlphaBuffer(true);
QQuickWindow *window = qobject_cast<QQuickWindow *>(topLevel);
QSurfaceFormat surfaceFormat = window->requestedFormat();
window->setFormat(surfaceFormat);
window->show();
}
}
main.qml:(重要部分)
import QtQuick 2.2
import QtQuick.Controls 1.1
import QtQuick.Controls.Styles 1.2
import QtQuick.Layouts 1.1
import QtQuick.Window 2.0
import com.cpp.mfcanvas 1.0
ApplicationWindow {
visible: true
width: 640
height: 480
title: qsTr("MFCanvas")
onSceneGraphInitialized: {
drawMenu.visible = true;
lineWidth.visible = true;
colorMenu.visible = true;
drawMenu.visible = false;
lineWidth.visible = false;
colorMenu.visible = false;
}
Rectangle {
id: main
anchors.fill: parent
property real toolsH: 15
property real iconW: 25
property real menuH: 8
property real menuW: 16
property real dpi: (Screen.logicalPixelDensity == undefined ? 6 : Screen.logicalPixelDensity) * 1.5
property color choosenColor: Qt.hsla(hue.value, saturation.value, luminance.value, 1)
Text {
anchors.centerIn: parent
font.pointSize: 60
text: "MFCanvas"
}
MFCanvas {
id: canvas
Component.onCompleted: {
canvas.resize(main.width, main.height);
}
}
//...
}
}
如果您需要任何其他信息,请告诉我。
先感谢您! =)
最佳答案
这里有很好的解释:
https://forum.qt.io/topic/64693
简而言之:不要尝试直接从输入事件处理程序中绘制, 但是在你的小部件中重载 paintEvent 方法并创建 QPainter 那里。独占使用输入事件修改内部 数据模型并在 paintEvent 中使用 QPainter 将其显示在输出路径上。
关于c++ - Qt:QWidget::paintEngine:不应再调用,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/25781353/