QComboBox Gradient Sample

1-ReadMe.md

Warning!

This gist was moved to:

https://github.com/EXL/Stuff/tree/master/Examples/Qt-GradientComboBox

GradientComboBox.pro

#-------------------------------------------------
#
# Project created by QtCreator 2014-08-29T17:55:26
#
#-------------------------------------------------

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = GradientComboBox
TEMPLATE = app


SOURCES += main.cpp\
        MainWindow.cpp

HEADERS  += MainWindow.h

FORMS    += MainWindow.ui

main.cpp

#include "MainWindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}

MainWindow.cpp

#include "MainWindow.h"
#include "ui_MainWindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    initializeComboBox();

    colorizeComboBox(ui->comboBox, Qt::green, Qt::red, Qt::yellow);
}

void MainWindow::initializeComboBox()
{
    const int n = 50;
    for (size_t i = 0; i <= n; ++i) {
        ui->comboBox->insertItem(i, QString::number(getValue(i), 'f', 2));
        // ui->comboBox->setItemData(i, colorGenerator(Qt::green, Qt::red, i, n), Qt::BackgroundRole);
    }
}

qreal MainWindow::getValue(int aStep)
{
    return (qreal) aStep / 10;
}

QColor MainWindow::colorGenerator(QColor aBegin, QColor aEnd, int aStep, int aSize) const
{
    qreal rB, gB, bB;
    qreal rE, gE, bE;
    aBegin.getRgbF(&rB, &gB, &bB);
    aEnd.getRgbF(&rE, &gE, &bE);

    QColor color;
    color.setRgbF(colorInterpolate(rB, rE, aStep, aSize),
                  colorInterpolate(gB, gE, aStep, aSize),
                  colorInterpolate(bB, bE, aStep, aSize));
    return color;
}

void MainWindow::colorizeComboBox(QComboBox *aComboBox, QColor aBegin, QColor aEnd, QColor aMiddle)
{
    int _size = aComboBox->count();
    int _middle = _size / 2;

    qreal rB, gB, bB;
    qreal rE, gE, bE;
    qreal rM, gM, bM;

    aBegin.getRgbF(&rB, &gB, &bB);
    aEnd.getRgbF(&rE, &gE, &bE);
    aMiddle.getRgbF(&rM, &gM, &bM);

    for (int i = 0; i < _size; ++i) {
        QColor color;
        if (aMiddle != Qt::transparent) {
            if (i < _middle) {
                color.setRgbF(colorInterpolate(rB, rM, i, _middle),
                              colorInterpolate(gB, gM, i, _middle),
                              colorInterpolate(bB, bM, i, _middle));
            } else {
                color.setRgbF(colorInterpolate(rM, rE, i - _middle, _middle),
                              colorInterpolate(gM, gE, i - _middle, _middle),
                              colorInterpolate(bM, bE, i - _middle, _middle));
            }
        } else {
            color.setRgbF(colorInterpolate(rB, rE, i, _size),
                          colorInterpolate(gB, gE, i, _size),
                          colorInterpolate(bB, bE, i, _size));
        }
        aComboBox->setItemData(i, color, Qt::BackgroundRole);
    }
}

qreal MainWindow::colorInterpolate(qreal aBegin, qreal aEnd, int aStep, int aSize) const
{
    return (aBegin < aEnd) ? qAbs(((aEnd - aBegin) * ((qreal) aStep / aSize)) + aBegin) :
                             qAbs(((aBegin - aEnd) * (1 - ((qreal) aStep / aSize))) + aEnd);
}

MainWindow::~MainWindow()
{
    delete ui;
}

MainWindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class QComboBox;

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private:
    void initializeComboBox();
    qreal getValue(int aStep);
    QColor colorGenerator(QColor aBegin, QColor aEnd, int aStep, int aSize) const;
    void colorizeComboBox(QComboBox *aComboBox, QColor aBegin, QColor aEnd, QColor aMiddle = Qt::transparent);
    qreal colorInterpolate(qreal aBegin, qreal aEnd, int aStep, int aSize) const;

private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

MainWindow.ui

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QMainWindow" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>400</width>
    <height>300</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>MainWindow</string>
  </property>
  <widget class="QWidget" name="centralWidget">
   <layout class="QVBoxLayout" name="verticalLayout">
    <item>
     <layout class="QGridLayout" name="gridLayout">
      <item row="0" column="1">
       <spacer name="verticalSpacer">
        <property name="orientation">
         <enum>Qt::Vertical</enum>
        </property>
        <property name="sizeHint" stdset="0">
         <size>
          <width>20</width>
          <height>40</height>
         </size>
        </property>
       </spacer>
      </item>
      <item row="1" column="0">
       <spacer name="horizontalSpacer">
        <property name="orientation">
         <enum>Qt::Horizontal</enum>
        </property>
        <property name="sizeHint" stdset="0">
         <size>
          <width>40</width>
          <height>20</height>
         </size>
        </property>
       </spacer>
      </item>
      <item row="1" column="1">
       <widget class="QComboBox" name="comboBox">
        <property name="minimumSize">
         <size>
          <width>120</width>
          <height>0</height>
         </size>
        </property>
       </widget>
      </item>
      <item row="1" column="2">
       <spacer name="horizontalSpacer_2">
        <property name="orientation">
         <enum>Qt::Horizontal</enum>
        </property>
        <property name="sizeHint" stdset="0">
         <size>
          <width>40</width>
          <height>20</height>
         </size>
        </property>
       </spacer>
      </item>
      <item row="2" column="1">
       <spacer name="verticalSpacer_2">
        <property name="orientation">
         <enum>Qt::Vertical</enum>
        </property>
        <property name="sizeHint" stdset="0">
         <size>
          <width>20</width>
          <height>40</height>
         </size>
        </property>
       </spacer>
      </item>
     </layout>
    </item>
   </layout>
  </widget>
 </widget>
 <layoutdefault spacing="6" margin="11"/>
 <resources/>
 <connections/>
</ui>

MediumColor.png

ScreenShot.png