GNIITSolution: A Professional HTML Renderer You Will Use

Sunday, 31 January 2016

A Professional HTML Renderer You Will Use

Introduction

This is a library of 100% managed code that draws beautifully formatted HTML. It comes along with three WinForms controls:

HtmlPanel
HtmlLabel
HtmlTooltip

And a static method ready to draw HTML:

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HtmlRenderer.Render(Graphics g, string html, RectangleF area, bool clip)

Note: The drawing engine is based on the CSS Level 2 specification.

Background

For years, I have been planning for a project like this. I prepared myself quite well. I went through the entire CSS Level 2 specification along with the HTML 4.01 specification.

One of the most interesting things I found is this: Drawing HTML is no more than laying out a bunch of boxes with borders margins and paddings. Once you overpass this paradigm, everything else is to help the code actually place the boxes on the right place, and then paint the string each box contains.

Imagine the power that drawing full-rich-formatted HTML on your controls can give to your applications. Use bold when you need it, italics on every message, and borders and fonts as you may like or need everywhere on the desktop application. One of the first projects where I will use it is on the tooltips of my Ribbon Project.

Although I have not tested it on mono yet, there should be no problem at all, since all of the code in the library is managed code and the methods it uses to paint are quite basic. It draws lines, rectangles, curves and text.

For now, the render looks really nice. Sometimes it can fool you to think you're using a real Web browser, trust me, download the demo, it is just an EXE and a DLL.

Using the Code

The library locates the code under the System.Drawing.Html namespace. The controls that renderHTML are under the System.Windows.Forms namespace.

The renderer follows the CSS Box Model. Box model is nothing but a tree of boxes, just as the tree ofHTML, each of these boxes is represented by a very used class called CssBox. The start node is represented by the class InitialContainer.

All the known CSS properties apply to each of these boxes. Each box may contain any number of child boxes and just one parent. The only box that has no parent at all is the so called Initial Container.

A typical use of an Initial Container to draw HTML would look like this:

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//Create the InitialContainer
InitialContainer c = new InitialContainer("<html>");
 
//Give bounds to the container
c.SetBounds(ClientRectangle);
 
//Measure bounds of each box on the tree
c.MeasureBounds(graphics);

//Paint the HTML document
c.Paint(graphics);

First a label, then a panel and at last a ToolTip, all of which support HTML rendering.

You may never use it, since I provided controls and methods that create this object for you.

HtmlPanel

A panel that is ready to accept HTML code via its Text property. Its full name isSystem.Windows.Forms.HtmlPanel.

The only properties you need to know are:

AutoScroll. Activates/Deactivates the auto-scroll capabilities as you know. It is set to true by default.
Text. Gets/Sets the HTML source.

The panel will update the bounds of the elements as you scroll or resize the control.

HtmlLabel

A label that is ready to accept HTML code via its Text property. Its full name isSystem.Windows.Forms.HtmlLabel.

The only properties you need to know are:

AutoScroll. Activates/Deactivates the auto-scroll capabilities as you know. It is set to true by default.
AutoSize. Sets the size of the label automatically if activated.
Text. Gets/Sets the HTML source.

Some interesting things:

The label will update the bounds of the elements as you scroll or resize the control.
The label can be transparent.
The panel has better performance than the label.

HtmlToolTip

Works exactly like the ToolTip you already know, with the little difference that this tooltip will renderHTML on it. It's full name is System.Windows.Forms.HtmlToolTip.

There are no properties here to learn. Use it just the way you use the ToolTip that comes with the framework. Internally, it just handles the OwnerDraw event.

Some Features of my Own

I took the liberty of adding a couple of features:

Background gradients
Rounded corners

These are achieved through the following CSS properties:

background-gradient: (color)
background-gradient-angle: (number)
corner-ne-radius: (length)
corner-nw-radius: (length)
corner-se-radius: (length)
corner-se-radius: (length)
corner-radius: (length){1,4} (shorthand for all corners)

What's Currently Supported by the Renderer?

Most border, padding and margin and positioning CSSproperties (except for the heightproperty)
Text alignment horizontally and vertically, text indents too
Lists, ordered and unordered. Advanced numbering is not yet supported
Tables, almost all of it. Cell combinations work quite well as far as I tested them
Fonts (partially) and Colors
Backgrounds (just color)

Points of Interest

What can I say, this is one of the most fun projects I've ever been involved with. And so far, it runs beautifully and checks its original design goals.

I am planning to give it full rendering support, to the day that you may visualize a web page just as a good web browser would; and why not, make a WYSIWYG HTML editor to give amazing HTMLediting power to your applications.

I'm also planning to make sure it runs perfectly well on Mono and on Mobile platforms.

In the next few days, I'll publish a list of supported HTML tags and CSS properties.

GNIITSolution

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