Skinning Engine

skinning_engine

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     Skinning Engine
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           Summary and Rationale
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           Current System
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           Requirements
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           Skinning Engine Proposals
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           How QT Quick and QML might be used in QT 4.7.x
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           Forum discussion
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           Ideas for Skinning Engines
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           Qt 4 based Skinning Engine

Skinning Engine Summary and Rationale

Status: This specification is in drafting. Please feel free to add comments.

Supported Widgets

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     Push-buttons
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     Multi-state push buttons
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     Sliders
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           horizontal or vertical
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     Text labels
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     Knobs
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     VU meter
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     Embed library widget
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     Status light

Requirements

Metadata/Manifest

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     Include the following metadata:
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           author
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           title
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           description
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           language
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           skin version
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           license
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           update-URL
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           suggested screen resolution
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           min screen resolution

Base Widget

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     Nameable
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     Position, Size
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           Potentially offer absolute positioning mode for legacy support, but in general deprecate absolute positioning.
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           Use size-hints (max-min size) instead of single size.
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     Tooltip
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     Connections
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           EmitOnDownPress and EmitOnRelease properties (to obviate need for double-connections)
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           Choose mouse button.
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     Tab ordering?

Widget Layout

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     Widget Grouping
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           Nameable
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           Have a size hint and optionally an absolute position.
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           Provide a hide/show-control. Uses the group's name.
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     Layouts
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           Allow a widget group to have a layout assigned to it.
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     Windows
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           Windows are the root of each hierarchy of widgets
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     Widget Templates
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           Ability to specify some template for a widget for saving time, sanity.

Widgets

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     Buttons
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           Allow multi-state button or push-button.
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           Support pixmaps for each button position
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           Allow non-pixmap buttons. Use QSS to styling.
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     Slider
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           Allow vertical or horizontal orientation
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           Separate image for slider and knob
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           Allow non-pixmap sliders. Use QSS for styling.
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     Drop-down Chooser
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           Allow styling via QSS.
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           No pixmap option, as it's text-only.
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     Knobs
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           Single knob image that is rotated plus background image.
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           Allow specification of 'translation' function (i.e. log-potmeter or potmeter)
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           Allow non-pixmap knobs. Use QSS for styling.
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     Library Widget
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           Still a monolithic widget. Don't think it adds value to allow much customization here.
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           Use QSS for all appearance styling.
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     Text labels
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           Make use of Controls to display text instead of hard-coding text.
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           Potentially allow scripts to dynamically affect what is shown.
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           Allow Marquee effect so you can read text that goes out of the control.
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     VU Meter
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           Allow QSS styling (how???) or pixmaps.
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     Status light
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           Connects to a control and dynamically switches its pixmap or QSS property based on the control's value
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     Datagrid Widget
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           Requirements unknown.
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     Video Widget
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           Requirements unknown.

Skinning Engine Proposals

Given the above requirements, list various proposals for skin formats here:

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     Qt4, Qt Style Sheet-based approach
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     Qt 4.7 QML/Kinetic-based approach
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     HTML/CSS Based Skins

The current ideas are: Qt 4 based Skinning Engine

Qt 4 is the cross-platform framework.

For the creation of a skinning system, Qt supports many things: layouts, style sheets, vector graphics, raster/OpenVG/OpenGL rendering, useful low-level painting system, XML, animation framework (since 4.6 or as official add-on), declarative UI technology (since 4.6)…

By combining some of these technologies it should be possible to create an advanced skinning engine for LMCE. To investigate

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     Explore QWidget versus QGraphicsView for layout.
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           How does the performance stack up?
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           QWidgets can be rendered in a QGV, but how does this affect performance?
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                 But when the visualization is rendered in OpenGL, we'll probably have to render the whole QGV in OpenGL
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           QGV will give us a really cool and flexible UI in combination with the Animation/DUI framework
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           QGV will give us fast software-based UI rendering, as well as support for rendering the UI through OpenGL and since Qt 4.6 also OpenVG
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     Explore if and how style sheets can help
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           Style sheets are very useful to skin stuff like scrollbars and other default widgets
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           The more important stuff like buttons should probably be skinned by reimplementing paintEvent, because this gives more possibilities
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                 Style sheets may be slower than reimplementing paintEvent - although it has to be investigated to be sure
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                 More advanced animations (besides simple hover/overroll effects) cannot be created with style sheets only

Pro

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     Support pixmap skins (porting of current skins will be easier this way, and performance will probably be higher than using SVG)
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     Support SVG skins (for those who want, SVG skins should be an option as well
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           Performance may be lower, but we could optionally render SVG as pixmaps to improve performance
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     Possibility to implement a layout system (because interface elements should not stretch)
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     The window itself should be themable/deformable too. Could be achieved by either composite or with a mask (or both)