绘制步骤

以交互绘制圆形为例：

1. 点击鼠标左键，确定圆心位置；
2. 抬起鼠标，移动鼠标，半径随鼠标位置变化；
3. 点击左键确定半径，完成圆的绘制。

绘制结果

Code

/// j-operator-create-circle.h#pragma once#include "j-operator.h"
#include "j-geometry/j-geometry-circle.h"namespace JNSOperator {enum class JCreateCircleStep {eCreateCircleStepInit = 0,eCreateCircleStepFirstDown,eCreateCircleStepFirstRelease,eCreateCircleStepSecondDown,eCreateCircleStepSecondRelease};class JOperatorCreateCircle : public JOperator {public:JOperatorCreateCircle(JOperatorManager *manager);virtual ~JOperatorCreateCircle();unsigned GetClassId() const override {return ID_OP_CREATE_CIRCLE;}bool IsOpDrawCircle() const override {return true;}void LButtonDown(const JNSGeometry::JGeoPoint &point) override;void LButtonUp(const JNSGeometry::JGeoPoint &point) override;void MouseMove(const JNSGeometry::JGeoPoint &point) override;void RButtonUp(const JNSGeometry::JGeoPoint &point) override;void BeforeOperate() override;void Reset() override;void EndOperate(JResult aResult) override;const JNSGeometry::JGeoCircle &GetAssistCircle();void SetCenterAndRadius(const JNSGeometry::JGeoPoint &center, double radius);JCreateCircleStep GetStatus();private:JNSGeometry::JGeoCircle assist_circle_;JCreateCircleStep step_ = JCreateCircleStep::eCreateCircleStepInit;};
}

/// j-operator-create-circle.cpp#include "j-operator/j-operator-create-circle.h"
#include "j-operator/j-operator-manager.h"
#include "j-document/j-document.h"namespace JNSOperator {JOperatorCreateCircle::JOperatorCreateCircle(JOperatorManager *manager): JOperator(manager) {Reset();}JOperatorCreateCircle::~JOperatorCreateCircle() {}void JOperatorCreateCircle::LButtonDown(const JNSGeometry::JGeoPoint &point) {if (step_ == JCreateCircleStep::eCreateCircleStepInit) {assist_circle_.SetCenter(point);step_ = JCreateCircleStep::eCreateCircleStepFirstDown;} else if (step_ == JCreateCircleStep::eCreateCircleStepInit ||step_ == JCreateCircleStep::eCreateCircleStepFirstDown ||step_ == JCreateCircleStep::eCreateCircleStepFirstRelease) {double radius = point.DistanceTo(assist_circle_.GetCenter());assist_circle_.SetRadius(radius);step_ = JCreateCircleStep::eCreateCircleStepSecondDown;}}void JOperatorCreateCircle::LButtonUp(const JNSGeometry::JGeoPoint &point) {if (step_ == JCreateCircleStep::eCreateCircleStepFirstDown) {assist_circle_.SetCenter(point);step_ = JCreateCircleStep::eCreateCircleStepFirstRelease;} else if (step_ == JCreateCircleStep::eCreateCircleStepSecondDown) {double radius = point.DistanceTo(assist_circle_.GetCenter());assist_circle_.SetRadius(radius);step_ = JCreateCircleStep::eCreateCircleStepSecondRelease;EndOperate(JResult::eOk);}}void JOperatorCreateCircle::MouseMove(const JNSGeometry::JGeoPoint &point) {if (step_ == JCreateCircleStep::eCreateCircleStepInit ||step_ == JCreateCircleStep::eCreateCircleStepFirstDown) {assist_circle_.SetCenter(point);} else if (step_ == JCreateCircleStep::eCreateCircleStepFirstRelease ||step_ == JCreateCircleStep::eCreateCircleStepSecondDown) {double radius = point.DistanceTo(assist_circle_.GetCenter());assist_circle_.SetRadius(radius);}}void JOperatorCreateCircle::RButtonUp(const JNSGeometry::JGeoPoint &point) {}void JOperatorCreateCircle::BeforeOperate() {}void JOperatorCreateCircle::Reset() {JNSGeometry::JGeoPoint center;center.InitInvalid();assist_circle_.SetCenter(center);assist_circle_.SetRadius(0.0);step_ = JCreateCircleStep::eCreateCircleStepInit;}void JOperatorCreateCircle::EndOperate(JResult aResult) {if (aResult == JResult::eOk) {if (!assist_circle_.GetCenter().IsValid()) {return;}auto circle = new JNSGeometry::JGeoCircle();circle->SetCenter(assist_circle_.GetCenter());circle->SetRadius(assist_circle_.GetRadius());op_manager_->GetDocument()->AddGeo(circle);} else {}Reset();op_manager_->BackToNormal();}const JNSGeometry::JGeoCircle &JOperatorCreateCircle::GetAssistCircle() {return assist_circle_;}void JOperatorCreateCircle::SetCenterAndRadius(const JNSGeometry::JGeoPoint &center, double radius) {assist_circle_.SetCenter(center);assist_circle_.SetRadius(radius);}JCreateCircleStep JOperatorCreateCircle::GetStatus() {return step_;}
}

/// j-view.cppvoid JView::DrawOperator(JNSOperator::JOperatorCreateCircle *op) {auto circle = op->GetAssistCircle();auto center = circle.GetCenter();DrawPoint(static_cast<JNSGeometry::JGeoPoint *>(&center));DrawCircle(static_cast<JNSGeometry::JGeoCircle *>(&circle));}

以此为模板，可以将绘制其它基本图元的功能补齐。