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Dial and StyleItem

Submitted by mimec on 2014-08-15

As I promised, I'm starting a new series of articles dedicated to QtQuick. When I started playing with QtQuick and the QtQuick Controls module, I noticed that it implements QtQuick equivalents of most widgets, and Dial is one of the few that are missing. Perhaps QDial is not a very frequently used widget, but in certain kinds of QtQuick applications, especially for mobile devices, a dial control can come in handy:

Dial

A bit of googling quickly revealed that a Dial control exists as an experimental part of the QtQuick Controls module (you can find it here), but for whatever reason it never made it into the official package.

Here's my final version of Dial.qml after some tweaking:

import QtQuick 2.2
import QtQuick.Controls 1.2
import QtQuick.Controls.Private 1.0

Control {
    id: root

    width: 100
    height: 100

    property alias minimumValue: range.minimumValue
    property alias maximumValue: range.maximumValue
    property alias value: range.value
    property alias stepSize: range.stepSize
    property alias pressed: mouseArea.pressed

    property bool notchesVisible: false
    property real notchSize: 1
    property bool activeFocusOnPress: false

    activeFocusOnTab: true

    Accessible.role: Accessible.Dial
    Accessible.name: range.value

    Keys.onLeftPressed: { range.value -= range.stepSize; }

    Keys.onRightPressed: { range.value += range.stepSize; }

    RangeModel {
        id: range
        minimumValue: 0
        maximumValue: 1
        stepSize: 0
        value: 0
    }

    MouseArea {
        id: mouseArea
        anchors.fill: parent
        hoverEnabled: true

        onPositionChanged: {
            if ( mouseArea.pressed )
                range.value = mouseArea.valueFromPoint( mouseArea.mouseX, mouseArea.mouseY );
        }

        onPressed: {
            range.value = mouseArea.valueFromPoint( mouseArea.mouseX, mouseArea.mouseY );
            if ( root.activeFocusOnPress )
                root.focus = true;
        }

        onWheel: { range.value += wheel.angleDelta.y * range.stepSize / 120.0; }

        function valueFromPoint( x, y ) {
            var yy = root.height / 2 - y;
            var xx = x - root.width / 2;

            var angle = ( xx || yy ) ? Math.atan2( yy, xx ) : 0;

            if ( angle < -Math.PI / 2 )
                angle += 2 * Math.PI;

            var dist = 0;
            var minv = range.minimumValue;
            var maxv = range.maximumValue;

            if ( minimumValue < 0 ) {
                dist = -range.minimumValue;
                minv = 0;
                maxv = range.maximumValue + dist;
            }

            var v = ( minv + ( maxv - minv ) * ( Math.PI * 4 / 3 - angle ) / ( Math.PI * 10 / 6 ) );

            if ( dist > 0 )
                v -= dist;

            return Math.max( range.minimumValue, Math.min( range.maximumValue, v ) );
        }
    }

    style: Qt.createComponent( "DialStyle.qml" )
}

Note: for copyright purposes, the code snippets are licensed under the BSD-style open source license, just like the original code.

The code is very straightforward. The internal RangeModel object is used for handling minimum, maximum and step values (the Slider uses it too). The valueFromPoint() function converts the position of the mouse to the angle and then to the actual value. I renamed "tickmarksEnabled" to "notchesVisible" and added "notchSize" for compatibility with QDial. I also removed "wrapping", because the underlying StyleItem doesn't support it anyway. Finally, I added the missing mouse wheel and keyboard support.

What about drawing the control? The original Dial contains a StyleItem, another internal component of QtQuick Controls, which uses the application's default QStyle to paint items so that they look just like widgets. Now, a little digression. Qt5 has two separate UI modules - QtGui for handling windows and QtWidgets which implements the widgets. The former can be used without the latter, for example if your applications uses OpenGL or QtQuick or a custom painting engine and doesn't need widgets. By excluding widgets, you can reduce dependencies by a few megabytes.

The QtQuick Controls can work perfectly fine without QtWidgets. However, in that case they are drawn using built-in bitmap images, and they look the same on all platforms. On the other hand, when QtWidgets are enabled, the QtQuick Controls use the StyleItem components, which emulate the "native" look of widgets on the given platform. To be more specific, the style used by QtQuick Controls depends on whether you are using QGuiApplication or QApplication (the former is part of QtGui; the latter is part of QtWidgets). This information is deeply buried in the Qt documentation, so it can be quite confusing. If you dig into the Qt sources, you will find that the QtQuick.Controls.Styles module actually contains two subdirectories: "Base" with platform-independent styles and "Desktop" with ones that use StyleItem. The internal QQuickControlSettings class is used to select the right styles at run-time, and you can even use the "QT_QUICK_CONTROLS_STYLE" environment variable to use an entirely different set of styles.

Back to the main topic, embedding a StyleItem directly in the Dial is not a good idea, because it only works with the QtWidgets module and it's not possible to implement a custom or platform-independent style. That's why I changed the code to use the "style" property of the "Control" component, decoupling the style from the control, just like other QtQuick Controls do. The default implementation of the style is based on the original code, so it uses the StyleItem to do the job:

import QtQuick 2.2
import QtQuick.Controls 1.2
import QtQuick.Controls.Private 1.0

Style {
    property Component panel: StyleItem {
        id: styleItem

        property real visualPos: control.maximumValue - control.value

        property real granularity: {
            if ( ( control.maximumValue - control.minimumValue ) < 10 )
                return 100;
            else if ( ( control.maximumValue - control.minimumValue ) > 1000 )
                return 1 / Math.ceil( ( control.maximumValue - control.minimumValue ) / 1000 );
            else
                return Math.floor( 1000 / ( control.maximumValue - control.minimumValue ) );
        }

        elementType: "dial"
        activeControl: control.notchesVisible ? "ticks" : ""
        hasFocus: control.focus
        enabled: control.enabled
        sunken: control.pressed
        maximum: control.maximumValue * styleItem.granularity
        minimum: control.minimumValue * styleItem.granularity
        value: styleItem.visualPos * styleItem.granularity
        step: Math.ceil( control.notchSize * styleItem.granularity )

        Behavior on visualPos {
            enabled: !control.pressed
            NumberAnimation {
                duration: 300
                easing.type: Easing.OutSine
            }
        }
    }
}

This code simply passes information from the control to the StyleItem. The only interesting part is the "granularity" property. The original code uses a hard-coded value of 100 instead. By increasing the number of steps internally, it's possible to have a nice looking, smooth animation when the Dial rotates. However, the hard-coded value of 100 doesn't always work, because the internal implementation of QStyle only paints the notches correctly if the total number of steps doesn't exceed 1000. That's why my code uses a dynamic granularity instead which works correctly in most cases.

A very simple, platform-independent implementation of the style could use a rotating image instead:

import QtQuick 2.2
import QtQuick.Controls 1.2
import QtQuick.Controls.Private 1.0

Style {
    property Component panel: Image {
        id: image

        property real visualPos: control.value

        source: control.pressed ? "dial-on.png" : "dial.png"
        rotation: 180 * 7 / 6 + ( image.visualPos - control.minimumValue ) * ( 180 * 10 / 6 )
            / ( control.maximumValue - control.minimumValue )

        Behavior on visualPos {
            enabled: !control.pressed
            NumberAnimation {
                duration: 300
                easing.type: Easing.OutSine
            }
        }
    }
}

In order to create the notches, you can place a small Rectangle in a Repeater and use appropriate rotation.

Hello, QtQuick!

Submitted by mimec on 2014-07-23

It's been a while... As usual, this means that there's been a lot going on and I simply didn't have time to write. However, I'm planning to start a new series of articles dedicated to QtQuick. It's been over 2 months since I started my adventure with QtQuick, so I have some initial observations of its strong and weak points that I would like to share.

I think that the biggest problem with QtQuick is that it's hugely undervalued. Unfortunately, there are some political reasons behind this. Major software companies try to tie developers to their platforms and platform-specific frameworks. It's no big surprise that Nokia had to get rid of Qt when it was purchased by Microsoft, even though in theory a good cross-platform framework should be a goldmine for the company who owns it. The result is that many people unduly consider Qt dead.

The reality is that QtQuick has a lot of potential. It's more powerful than HTML5 when it comes to rich, platform-independent UI, and it's supported by powerful back-end Qt modules. It's free even for commercial use, and it's quite mature and still actively developed. It also supports both mobile and desktop platforms. Of course, there are also disadvantages. First, in order to use QtQuick you need to learn QML, which is not as easy as it seems, especially when attempting to create complex applications. Second, QtQuick (and Qt in general) is a toolkit, not a framework, so you have to lay down a lot of foundation before you can start being productive developing the actual application. Finally, the documentation is quite poor, and there is not too much open source code using QtQuick that you can peak into, so it's often difficult to find any useful information about a problem you're trying to solve. Because of that, learning QtQuick requires a bit of trial and error approach, but from what I can tell so far, it's worth the effort.

Apart from the fact that QtQuick has many ready to use UI components (including the Quick Controls), there are also additional benefits from writing the application partially in QML and partially in C++. When the UI is written entirely in QML, it can be designed by people with graphical skills, who don't necessarily need to know low level programming languages like C++. It's similar to how HTML/CSS templates are created independently from PHP (or whatever) code in web applications. Also the UI of the application can be fully tested without writing a single line of C++ code, which is great for rapid design and prototyping. To make it possible, simple stubs (mock objects) for application logic can be written in QML. When using a simple MVP or MVC pattern it's also possible to easily switch views - for example between the desktop and mobile versions of the application. I will write more about it in one of the next articles.

Life goes on

Submitted by mimec on 2014-04-24

Mister Tins is now officially in sale, which means it's officially dead, and that's not a big surprise to me. I guess it's time for a brief post-mortem summary of what went right and what went wrong. Well, the good thing is that I finished it, and it was fun, not to mention that my long time dream to make a game has come true :). I still think it was quite a good idea, and a bit underrated, but looking back I think there are at least three reasons why this whole project was doomed from the beginning:

  • Modern games are driven by artists, not by developers. It's just no longer "let's do the hard work and write the whole code and then we'll just throw in a few textures and the game will be ready". On the contrary, you take an existing engine like Unity, and then all the hard work is graphics, models, animations; the programming comes down to scripting a few events. I'm oversimplifying, but you get the point.
  • Modern games take a lot of work. Even a simple indie game requires a team of at least a few dedicated persons and often takes years, especially when people have another full time job. I spent six months, but in reality only during the first few weeks I spent significant time on this project. It's good that I started with something simple enough that I was able to finish it, but it can't compete with all the professional games in the market.
  • Another thing, which is perhaps not a strong requirement, but certainly helps, is when you can participate in various events and shows, contact other game developers, potential players and especially the press, long before your game is finished. Obviously, it's easier when you live in a large city in USA or Canada, not in some shithole in Poland…

In conclusion, if I'm ever going to get involved in another game, I'd certainly be joining an existing, dedicated team of artists, who need a coding monkey, and I'd teach myself Unity. Anyway, it's not going to happen very soon :). The good news is that now I finally have some time to release a new version of Saladin and WebIssues, work on redesigning my book, and simply read and play some games.

Also in my personal life there have been some changes recently; for example, I'm getting a divorce. I could make a similar list of things that went wrong, but I will spare you the details. Let's just say that one day you think you know someone, and then it turns out that your goals and values are so different that you simply can't go on any further. At first I was really upset because I hoped our son could have a "normal" family, especially that I din't have one, but the truth is that now I spend much more time with him than before we separated, and I'm definitely going to do everything I can to make it up for him. So I went through the whole denial-anger-regret stages and in the end I think it's for the better for all of us.

Luckily, there have been some positive changes too. I renewed an old friendship and made a new one, and that's something you can't overvalue. It also may have bigger consequences, because I think that I finally found a team of dedicated people and we have a chance to work on a very interesting and promising project - maybe it's not a game, but it's not one of those boring warehouse/financial/enterprise kind of applications either. So, life goes on…

Mister Tins released

Submitted by mimec on 2014-01-08

I just released the first beta version of Mister Tins. You can download it for free and play the first five levels in demo mode. For now the full version is only available for beta testers and press, if you're interested then please contact me. In a nutshell, Mister Tins is a puzzle indie game for PC in a top-down perspective view. The goal is to move boxes to open doors, jump between platforms and different floors, avoid obstacles and find the exit from a labyrinth of rooms.

Here's the official trailer of the game:

You can find more information about the game on the official blog of the MiMec Games team.

Issues and Tins

Submitted by mimec on 2013-11-13

Today I released version 1.1 of WebIssues, a major release which introduces lots of very nice and useful features. I must admit that I'm relieved that this project is finally over. It's also perfect timing, because I'm getting seriously involved in the indie game which I announced some time ago. The game is now officially called Mister Tins and it even already has a Facebook page and a blog (where I will probably post more often than here in the nearest future).

What started as a quick test project, has now become a playable and quite enjoyable game (at least for me). It's still very far from the first official release, but at least now I'm convinced that this is really what I want to do. It's what I always wanted to do and what I probably should have done a long time ago.

I'm not saying that I regret what I've been doing for the last few years. I definitely wouldn't be half as good programmer if it wasn't for WebIssues. I would even go as far as saying that I wouldn't be half the person I am today if it wasn't for all the open source projects I've been involved in. All this technical and non-technical experience should now pay off with this new project.

Of course, there's no guarantee that I will succeed. I know that there is a lot of potential in what I'm doing, and the whole idea of the game, while simple, seems quite innovative. On the other hand, there are many factors involved, and not all of them depend on me. A lot of luck is needed to provide what people need exactly in the right moment. Also, creating games is a team sport, and experience taught me that finding the right team members is not easy an task. But the best thing is that I've reached one very major goal, which was releasing WebIssues 1.1, and I can immediately concentrate on the next goal, without losing the momentum that I have.