1、概述
源码放在文章末尾

该项目实现了灵动的小鱼，可以在界面上跟随鼠标点击自由的游泳，项目demo演示如下所示：

项目部分代码如下所示：

#include "magicfish.h"
#include <QtMath>
#include <QPainter>
#include <QPainterPath>
#include <QVariantAnimation>MagicFish::MagicFish(QQuickPaintedItem *parent): QQuickPaintedItem(parent),m_fishRadius(30),m_finLen(30 * 1.3),m_bodyHeight(30 * 3.2),m_headAlpha(200),m_bodyAlpha(225),M_finAlpha(120),m_mainAngle(0.0),m_curValue(0),m_wave(1.0),m_startFin(false),m_paintPoint(false)
{m_animation = new QVariantAnimation(this);m_animation->setDuration(180 * 1000);m_animation->setStartValue(0);m_animation->setEndValue(54000);m_animation->setLoopCount(-1);connect(m_animation, &QVariantAnimation::valueChanged, this, [this](const QVariant &value){m_curValue = value.toInt();update();});connect(this, &QQuickItem::widthChanged, this, &MagicFish::resize);connect(this, &QQuickItem::heightChanged, this, &MagicFish::resize);m_animation->start();
}void MagicFish::paint(QPainter *painter)
{painter->setRenderHint(QPainter::Antialiasing);QPointF middle_pos = QPointF(width() / 2, height() / 2);m_headPos = calcPoint(middle_pos, m_bodyHeight / 2.0, m_mainAngle);paintMyPoint(painter, m_headPos);paintMyPoint(painter, middle_pos);painter->setPen(Qt::NoPen);painter->setBrush(QBrush(QColor(20, 203, 232, 50)));painter->setBrush(QBrush(QColor(244, 92, 71, m_headAlpha)));painter->drawEllipse(m_headPos, m_fishRadius, m_fishRadius);qreal angle = m_mainAngle + qSin(qDegreesToRadians(m_curValue * 1.2 * m_wave)) * 2;QPointF end_pos = calcPoint(m_headPos, m_bodyHeight, angle - 180);QPointF pos1 = calcPoint(m_headPos, m_fishRadius, angle - 80);QPointF pos2 = calcPoint(end_pos, m_fishRadius * 0.7, angle - 90);QPointF pos3 = calcPoint(end_pos, m_fishRadius * 0.7, angle + 90);QPointF pos4 = calcPoint(m_headPos, m_fishRadius, angle + 80);QPointF central_left = calcPoint(m_headPos, m_bodyHeight * 0.56, angle - 130);QPointF central_right = calcPoint(m_headPos, m_bodyHeight * 0.56, angle + 130);QPainterPath path;path.moveTo(pos1);path.quadTo(central_left, pos2);path.lineTo(pos3);path.quadTo(central_right, pos4);path.lineTo(pos1);painter->setBrush(QBrush(QColor(244, 92, 71, m_bodyAlpha)));painter->drawPath(path);paintMyBody(painter, end_pos, m_fishRadius * 0.7, 0.6, angle);QPointF left_fin_pos = calcPoint(m_headPos, m_fishRadius * 0.9, angle + 110);paintMyFishFins(painter, left_fin_pos, true, angle);QPointF right_fin_pos = calcPoint(m_headPos, m_fishRadius * 0.9, angle - 110);paintMyFishFins(painter, right_fin_pos, false, angle);
}void MagicFish::resize()
{m_fishRadius = qMin(width(), height()) / 10.0;m_finLen = m_fishRadius * 1.3;m_bodyHeight = m_fishRadius * 3.2;
}QPointF MagicFish::calcPoint(const QPointF &pos, qreal length, qreal angle)
{qreal delta_x = qCos(qDegreesToRadians(angle)) * length;qreal delta_y = qSin(qDegreesToRadians(angle - 180)) * length;return QPointF(pos + QPointF(delta_x, delta_y));
}void MagicFish::paintMyPoint(QPainter *painter, const QPointF pos)
{if(m_paintPoint){painter->save();painter->setPen(QPen(Qt::black, 3));painter->setBrush(QBrush(Qt::black));painter->drawPoint(pos);painter->restore();}
}void MagicFish::paintMyFishFins(QPainter *painter, const QPointF &pos, bool is_left, qreal father_angle)
{qreal contral_angle = 115;qreal fin_angle = m_startFin ? qSin(qDegreesToRadians(m_curValue * 16.1 * m_wave)) * 12.0 : 2;QPainterPath path;path.moveTo(pos);QPointF end_pos = calcPoint(pos, m_finLen, is_left ? father_angle + fin_angle + 180 :father_angle - fin_angle - 180);QPointF control_pos = calcPoint(pos, m_finLen * 1.8, is_left ?father_angle + contral_angle + fin_angle :father_angle - contral_angle - fin_angle);path.quadTo(control_pos, end_pos);path.lineTo(pos);painter->save();painter->setBrush(QBrush(QColor(244, 92, 71, M_finAlpha)));painter->drawPath(path);painter->restore();
}void MagicFish::paintMyBody(QPainter *painter, const QPointF &pos, qreal seg_r, qreal MP, qreal father_angle)
{qreal angle = father_angle + qCos(qDegreesToRadians(m_curValue * 1.5 * m_wave)) * 15;qreal length = seg_r * (MP + 1);QPointF end_pos = calcPoint(pos, length, angle - 180);QPointF pos1 = calcPoint(pos, seg_r, angle - 90);QPointF pos2 = calcPoint(end_pos, seg_r * MP, angle - 90);QPointF pos3 = calcPoint(end_pos, seg_r * MP, angle + 90);QPointF pos4 = calcPoint(pos, seg_r, angle + 90);painter->save();painter->setBrush(QBrush(QColor(244, 92, 71, m_headAlpha)));painter->drawEllipse(pos, seg_r, seg_r);painter->drawEllipse(end_pos, seg_r * MP, seg_r * MP);QPainterPath path;path.moveTo(pos1);path.lineTo(pos2);path.lineTo(pos3);path.lineTo(pos4);painter->drawPath(path);painter->restore();paintMyBody2(painter, end_pos, seg_r * 0.6, 0.4, angle);
}void MagicFish::paintMyBody2(QPainter *painter, const QPointF &pos, qreal seg_r, qreal MP, qreal father_angle)
{qreal angle = father_angle + qSin(qDegreesToRadians(m_curValue * 1.5 * m_wave)) * 35;qreal length = seg_r * (MP + 2.7);QPointF end_pos = calcPoint(pos, length, angle - 180);QPointF pos1 = calcPoint(pos, seg_r, angle - 90);QPointF pos2 = calcPoint(end_pos, seg_r * MP, angle - 90);QPointF pos3 = calcPoint(end_pos, seg_r * MP, angle + 90);QPointF pos4 = calcPoint(pos, seg_r, angle + 90);paintMyTail(painter, pos, length, seg_r, angle);painter->save();painter->setBrush(QBrush(QColor(244, 92, 71, m_headAlpha)));painter->drawEllipse(end_pos, seg_r * MP, seg_r * MP);QPainterPath path;path.moveTo(pos1);path.lineTo(pos2);path.lineTo(pos3);path.lineTo(pos4);painter->drawPath(path);painter->restore();
}void MagicFish::paintMyTail(QPainter *painter, const QPointF &pos, qreal length, qreal max_w, qreal angle)
{qreal w = qAbs(qSin(qDegreesToRadians(m_curValue * 1.7 * m_wave)) * max_w + m_fishRadius / 5.0 * 3.0);QPointF end_point1 = calcPoint(pos, length, angle - 180);QPointF end_point2 = calcPoint(pos, length - 10, angle - 180);QPointF pos1 = calcPoint(end_point1, w, angle - 90);QPointF pos2 = calcPoint(end_point1, w, angle + 90);QPointF pos3 = calcPoint(end_point2, w - m_fishRadius / 1.5, angle - 90);QPointF pos4 = calcPoint(end_point2, w - m_fishRadius / 1.5, angle + 90);QPainterPath path;path.moveTo(pos);path.lineTo(pos3);path.lineTo(pos4);path.lineTo(pos);painter->save();painter->setBrush(QBrush(QColor(244, 92, 71,     m_headAlpha)));painter->drawPath(path);path.closeSubpath();path.moveTo(pos);path.lineTo(pos1);path.lineTo(pos2);path.lineTo(pos);painter->drawPath(path);painter->restore();
}void MagicFish::setWave(qreal value)
{m_wave = value;
}qreal MagicFish::getFishR() const
{return m_fishRadius;
}qreal MagicFish::getAngle()
{return m_mainAngle;
}QRectF MagicFish::geometry() const
{return QRectF(x(), y(), width(), height());
}QPointF MagicFish::getHeadPos() const
{return m_headPos;
}void MagicFish::setCurrentAngle(qreal angle)
{m_mainAngle = angle;update();
}void MagicFish::setFinAnimation(bool start)
{m_startFin = start;
}void MagicFish::setFishR(int value)
{m_fishRadius = value;m_finLen = value * 1.3;m_bodyHeight = value * 3.2;update();
}

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