QT custom window fillets

Qt Setting fillet

stay Qt There are two ways to set window fillets in ,

• QSS
• adopt paintEvent Self drawing window

QSS Setting fillet

This method of setting fillets is relatively flexible , But we set the base class window ( Outermost window ) use qss It's not convenient , Will receive follow-up qss Influence , In addition, when the fillet size exceeds the height 1/2 when , The fillet effect will disappear , So when the window changes dynamically , This is not convenient to use

border-radius:8px;// Four corners
border-top-left-radius:8px; top left corner ;
border-top-right-radius:8px; Upper right corner ;
border-bottom-left-radius:8px; The lower left corner ;
border-bottom-right-radius:8px; The lower right corner ;

paintEvent Self drawing window

The most common is to draw four corners at the same time

void CustomRadiusWidget::paintEvent(QPaintEvent *event)
{
    
	QPainter painter(this);
	painter.setRenderHint(QPainter::Antialiasing);
	painter.setBrush(bg_color_);
	painter.setPen(Qt::transparent);
	painter.drawRoundedRect(rect(), radius_, radius_);
}

But this time , If we want to achieve something like qss Let one or several corners realize rounded corners , It's not going to work , I checked it and found nothing related demo. Here I would like to share with you my ideas for implementation
The core idea is ： Draw four fillets , Then add a rectangle with edges and corners on the unwanted fillets to cover

Take the upper left corner for example

Core code

void CustomRadiusWidget::paintEvent(QPaintEvent *event)
{
    
	// Beautification style , Prevent the set fillet from being too large （ Over height 1/2）
	auto half_height = height() / 2;
	auto radius = radius_ > half_height ? height() / 2 : radius_;
	//auto radius = radius_;
	QPainter painter(this);
	QPainterPath draw_path;
	draw_path.addRoundedRect(rect(), radius, radius);
	draw_path.setFillRule(Qt::WindingFill);
	if (!left_top_) {
    
		draw_path.addRect(0, 0, width() / 2, height() / 2);
	}
	if (!left_bottom_) {
    
		draw_path.addRect(0, height() / 2, width() / 2, height() / 2);
	}
	if (!right_top_) {
    
		draw_path.addRect(width() / 2, 0, width() / 2, height() / 2);
	}
	if (!right_bottom_) {
    
		draw_path.addRect(width() / 2, height() / 2, width() / 2, height() / 2);
	}
	painter.setRenderHint(QPainter::Antialiasing);
	painter.setPen(Qt::transparent);
	painter.setBrush(bg_color_);
	painter.drawPath(draw_path);
}

QPainterPath Populate the rule

• Qt::OddEventFill（ Parity fill rule ） Determine whether a point is within the shape , Draw a horizontal line from this point to the position outside the shape , And calculate the number of intersections . If the number of intersections is odd , The point is inside the shape . This mode is the default .
• Qt::WindingFill ( Non zero bending rule ） Determine whether a point is within the shape , Draw a horizontal line from this point to the outside of the shape . Determine whether the direction of the line at each intersection is up or down . The number of windings is determined by summing the directions of each intersection . If the number is not zero , The point is inside the shape . This filling pattern can also be considered as the intersection of closed shapes in most cases .
  
  By the above code , You can control which fillet is displayed at will
  Complete code

//===================================.h==========================================//
#pragma once
#include <QWidget>
class CustomRadiusWidget : public QWidget
{
    
	Q_OBJECT
public:
	CustomRadiusWidget(QWidget *parent=nullptr);
	~CustomRadiusWidget();
	void SetRadius(int radius);
	void SetRadiusEnable(bool left_top, bool left_bottom, bool right_left, bool right_bottom);
protected:
	virtual void paintEvent(QPaintEvent* event)override;
private:
	int radius_ = {
    0};
	QColor bg_color_ = {
    106 ,90 ,205};
	bool left_top_=false;
	bool left_bottom_ = false;
	bool right_top_ = false;
	bool right_bottom_ = false;
};
//===================================.cpp==========================================//
#include "CustomRadiusWidget.h"
#include <QPainter>
#include <QPainterPath>
CustomRadiusWidget::CustomRadiusWidget(QWidget *parent) : QWidget(parent){
    
	setWindowFlag(Qt::FramelessWindowHint);
	setAttribute(Qt::WA_TranslucentBackground, true);
}

CustomRadiusWidget::~CustomRadiusWidget() {
    }

void CustomRadiusWidget::SetRadius(int radius){
    
	radius_ = radius;
}

void CustomRadiusWidget::SetRadiusEnable(bool left_top, bool left_bottom, bool right_top, bool right_bottom){
    
	left_top_ = left_top;
	left_bottom_ = left_bottom;
	right_top_ = right_top;
	right_bottom_ = right_bottom;
}

void CustomRadiusWidget::paintEvent(QPaintEvent *event)
{
    
	auto half_height = height() / 2;
	auto radius = radius_ > half_height ? height() / 2 : radius_;
	QPainter painter(this);
	QPainterPath draw_path;
	draw_path.addRoundedRect(rect(), radius, radius);
	draw_path.setFillRule(Qt::WindingFill);
	if (!left_top_) {
    
		draw_path.addRect(0, 0, width() / 2, height() / 2);
	}
	if (!left_bottom_) {
    
		draw_path.addRect(0, height() / 2, width() / 2, height() / 2);
	}
	if (!right_top_) {
    
		draw_path.addRect(width() / 2, 0, width() / 2, height() / 2);
	}
	if (!right_bottom_) {
    
		draw_path.addRect(width() / 2, height() / 2, width() / 2, height() / 2);
	}
	painter.setRenderHint(QPainter::Antialiasing);
	painter.setPen(Qt::transparent);
	painter.setBrush(bg_color_);
	painter.drawPath(draw_path);
}