tutorial.txt

=====================
eZ Components - Graph
=====================

.. contents:: Table of Contents
   :depth: 2

Introduction
============

The Graph component enables you to create line, pie and bar charts. The
output driver mechanism allows you to create different image types from each
chart, and the available renderers make the chart output customizable from
simple two-dimensional charts to beautiful three-dimensional data
projections. 

ezcGraph separates different parts of the graph into chart elements, each
representing one part of a graph. Elements include the title, the legend or an
axis, and are all independently configurable. This design not only allows you to use
different colors or fonts for each chart element, but also to define their
position and size. The main chart elements are the same for all chart types.
To define overall layouts for graphs, you can use palettes,
which specify default colors, symbols, fonts and spacings.

Data is provided through ezcGraphDataSet objects, which are normally created
from simple arrays. You also can perform statistical operations on data, as you
will see later.

Class overview
==============

This section gives you an overview of the most important classes.

ezcGraphChart
  Line, bar and pie charts extend this abstract class, which represents the
  chart to be rendered. ezcGraphChart collects the data and chart elements,
  gives you access to all configuration settings and calls the driver and
  renderer for creating the final output.

ezcGraphDataSet
  All datasets extend this abstract class to provide the data in a general
  form accessible by the chart.

ezcGraphChartElement
  All chart elements store configuration values that define their layout. An
  element's layout definition contains background, border, margin, padding and
  font configuration. ezcGraphChartElement is extended by other classes for the
  legend, text, background and different axis types.

ezcGraphChartElementAxis
  This class extends ezcGraphChartElement and is the base class for all axes.
  There are different axis types for different data to be displayed, such as
  numeric axis, string labeled axis or date axis.

ezcGraphAxisLabelRenderer
  This class defines the rendering algorithm for labels and grids on an axis.
  The distinction between algorithms is necessary, because bar charts have
  labels placed directly below the data point, but numerical data in line
  charts should be placed next to the grid.

ezcGraphPalette
  ezcGraphPalette contains color, font, symbol and spacing definitions to be
  applied to the entire graph.

ezcGraphRenderer
  This renderer transforms chart primitives, like pie chart segments, legend
  or data lines, to image primitives. You have the choice between a two- and
  three-dimensional renderer.

ezcGraphDriver
  This driver renders image primitives to an image. The default driver
  will output as SVG, but you can also render JPEGs or PNGs using ext/gd.

Chart types
===========

Pie charts
----------

The following is a simple example of how to create a pie chart using the
default driver, palette and renderer.

.. include:: tutorial/tutorial_simple_pie.php
   :literal:

Simply create a new chart object, optionally set a title for the chart,
assign the data and render it. To assign data, the dataset container
is accessed like an array to define an identifier for the dataset. The
dataset in this example is created from an array, where the keys are used as
the identifiers for the data points.

Pie charts accept only one dataset, and the data point identifiers are used to
create the legend. To generate the output, the default SVG renderer is used
with the default 2D renderer. By default, the colors are applied from the Tango
palette, from the Tango Desktop Project: http://tango.freedesktop.org/Tango_Desktop_Project

Several dataset and data point presentation styles will be mentioned in this
tutorial. One possibility is to highlight a special dataset or point. In line
15, the data point Opera is highlighted; in the case of pie charts, this
segment is pulled away from the center. See the renderer options class
ezcGraphRendererOptions for more details.

.. image:: img/tutorial_simple_pie.svg.png
   :alt:   Sample pie chart 

Pie chart options
~~~~~~~~~~~~~~~~~

There are several pie chart specific configuration options available. In
eZ Components, options are always accessed via public properties. For a full
list of all available options, see the documentation for the
ezcGraphPieChartOptions class.

.. include:: tutorial/tutorial_pie_options.php
   :literal:

In line 16, a sprintf format string is set, which defines how the labels are
formatted. Instead of a sprintf format string, you could also set a callback
function to do label formatting.

In this example, we set a custom sum to force the pie chart to show the
complete 100%. The percentThreshold lets the chart collect all data points that
have less than the specified percentage to be aggregated in one data point. We
also could define an absolute threshold, so that all data below a certain value
would be aggregated in one data point. summarizeCaption defines the caption for
this aggregated dataset.

.. image:: img/tutorial_pie_options.svg.png
   :alt:   Pie chart configuration options

Line charts
-----------

Line charts are created in the same way as pie charts, but they
accept more than one dataset. We are using the default driver, palette and
renderer in this example.

.. include:: tutorial/tutorial_line_chart.php
   :literal:

There are only two differences compared to the last example. In line 6, we
instantiate a ezcGraphLineChart object instead of ezcGraphPieChart and beginning in
line 10, we assign multiple datasets from an array we included earlier in the
script. The array in the file tutorial_wikipedia_data.php is built like this::

    <?php
    return array(
        'English' => array(
            'Jan 2006' => 965,
            'Feb 2006' => 1000,
            ...
        ), 
        ...
    );
    ?>

The result is a simple, default line chart.

.. image:: img/tutorial_line_chart.svg.png
   :alt:   Simple line chart

Bar charts
----------

Bar charts are very similar to line charts. They accept the same datasets and
only define another default dataset display type and axis label renderer.

.. include:: tutorial/tutorial_bar_chart.php
   :literal:

As you can see in line 6, we only change the chart constructor, and the
other default values are applied.

.. image:: img/tutorial_bar_chart.svg.png
   :alt:   Simple bar chart

Lots of bars
~~~~~~~~~~~~

By default, ezcGraph reduces the amount of steps shown on an axis to about 10
steps. This may cause unexpected results when trying to draw a bar chart
with more than 10 bars in one dataset. You may override the behaviour by
manually setting the amount of steps on the x axis::

	<?php
	// Initialize graph ...
	$graph->xAxis->labelCount = count( $chart->data['name'] );
	// Output graph ...
	?>

This works because all datasets implement the Countable interface. If you want
to use it for more than one dataset, you could do the following::

	<?php
	// Initialize graph ...
	$chart->xAxis->labelCount = max(
		count( $chart->data['name 1'] ),
		count( $chart->data['name 2'] )
	);
	// Output graph ...
	?>

Combining bar and line charts
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The only difference between bar and line charts is the display type of the
dataset and the axis label renderer of the x-axis. You can use one of those
constructors and modify your chart to display one or more datasets in
either display type. The axis label renderer is described later in this
tutorial.

.. include:: tutorial/tutorial_bar_line_chart.php
   :literal:

After creating the datasets we modify one of the datasets in line 14 to change
the default display type to ezcGraph::LINE. To more prominently display the
line, we set one graph option in line 16. Options are accessed like public
properties and in this case we set an option for the graph called "fillLines",
which indicates what transparency value is used to fill the space underneath
the line. Alternatively you can set "fillLine" on individual datasets.

.. image:: img/tutorial_bar_line_chart.svg.png
   :alt:   Combined bar and line chart

More bar chart options
~~~~~~~~~~~~~~~~~~~~~~

There are some more options available for line and bar charts, which configure
the highlighting of datasets.

.. include:: tutorial/tutorial_bar_options.php
   :literal:

In line 20, the size of the highlight boxes is specified and lines 22 to
24 change the font configuration for the highlight boxes. Highlighting
works in much the same way as for pie charts, but in line and bar charts it
makes sense to highlight a complete dataset instead of only one single data
point. This is because there is usually more than one dataset in
line and bar charts.

.. image:: img/tutorial_bar_options.svg.png
   :alt:   Configured highlight in combined line and bar chart

Stacked bar charts
~~~~~~~~~~~~~~~~~~

In stacked bar charts, the bars are not drawn next to each other, but
aggregated in one bar, and the overall bar consumes the space of the sum of all
single bars.

.. include:: tutorial/tutorial_stacked_bar_chart.php
   :literal:

To use stacked bar charts, you only need to set the option $stackBars to "true".
In the 3D renderer this will cause all bars to be rendered with the symbol
ezcGraph::NO_SYMBOL.

.. image:: img/tutorial_stacked_bar_chart.svg.png
   :alt:   Bar chart with stacked bars

Radar charts
------------

Radar charts are very similar to line charts, but only with one axis, which
will be drawn multiple times, rotated around the center point of the chart.

.. include:: tutorial/tutorial_radar_chart.php
   :literal:

This again is one of the simplest ways to create a radar chart. Nearly all
options described later are also available in radar charts. The basic
difference is that an ezcGraphRadarChart object is created in line 6.
Radar charts accept multiple datasets, like bar and line charts. In line 14
the first element of the dataset is reassigned as the last element to close
the circle. By not reassigning this value, you can get a radar chart where
the tails do not join.

.. image:: img/tutorial_radar_chart.svg.png
   :alt:   Simple radar chart

Controlling radar axis
~~~~~~~~~~~~~~~~~~~~~~

Instead of having an x and a y axis, the radar chart has a main axis, which is
the equivalent to the y axis in the other charts, and a rotation axis, the
equivalent of the x axis. The steps on the rotation axis define the positions
of the rotated main axis. This way you may use all available datasets and
axes.

.. include:: tutorial/tutorial_complex_radar_chart.php
   :literal:

The settings on the graph will be explained later in the tutorial in detail.
In line 11 the type of the rotation axis is set to a numeric axis, which is
explained in `Chart elements`_ -> `Axis`_.

For line 15 to 23, a dataset is added with some random data. Using this
data as a base, a new dataset is built, which calculates a polynomial
interpolation function. This is described in more detail in the
section `Datasets`_ -> `Average polynomial dataset`_. Lastly, the default colors
and symbols from the palette are modified.

.. image:: img/tutorial_complex_radar_chart.svg.png
   :alt:   Complex radar chart

The resulting radar chart shows how minor steps on the rotation axis are drawn
as a grayed out axis and major steps as a regular axis. Note that all
types of datasets can be drawn using radar charts.

Odometer charts
---------------

Odometer charts can display values on one bar with a gradient and markers,
providing a nice way for the viewer to detect where a value is in a defined
bounding.

.. include:: tutorial/tutorial_odometer_chart.php
   :literal:

As you can see from the example, the odometer basically behaves like other
chart types. First we create an object of the class ezcGraphOdometerChart, then
a title and a dataset is assigned, as per usual. Similar to pie charts, an
odometer only accepts one dataset. A legend does not exist for odometers - and
you may of course assign an array dataset, containing only one element.

.. image:: img/tutorial_odometer_chart.svg.png
   :alt:   Simple odometer

The result is a bar, filled with the default gradient, with markers as
indicators for the values on the bar. The axis span is automatically calculated
for the provided values - you can modify them as usual, but take a look at the
next example for this.

Custom odometer chart
~~~~~~~~~~~~~~~~~~~~~

When using only one value on an odometer chart, you may wish to manually
configure the span on the axis. You can do this as you normally would with
any other axis.

.. include:: tutorial/tutorial_custom_odometer_chart.php
   :literal:

In this example we only assign one value, so we get one marker on the
odometer. The we start using the configuration options for odometers, defined in
the ezcGraphOdometerChartOptions class.

The start and end color define the colors used for the background gradient. The
border options define the border, which is drawn around the chart gradient.
After this you can configure the width of the markers, and the space
used for the actual odometer.

We then configure the minimum and maximum values for the axis and a label for
the axis.

.. image:: img/tutorial_custom_odometer_chart.svg.png
   :alt:   Custom configured odometer 

Palettes
========

ezcGraph offers graph palettes to define the overall style properties of
chart elements. The style properties are similar to those from CSS:

- color
- background color
- border color
- border width
- padding
- margin
- dataset symbols

There are several predefined palettes in ezcGraph, but you can
easily modify them or create your own palettes.

Using a predefined palette
--------------------------

You can assign each class extending ezcGraphPalette to the palette
property of your graph. You should do this before adding datasets, because the
datasets request colors from the palette. If you set the palette after
creating the datasets, the datasets will still use the colors from the 
default palette.

.. include:: tutorial/tutorial_user_palette.php
   :literal:

The generated output differs quite a lot from the output using the default
Tango palette. The colors for the background, datasets and fonts have been
changed. Additionally, the palette sets a color for the major and minor grid, and
defines a border width and color for the chart elements. The palette defaults
to a sans-serif font and increases the margin between the chart elements.

.. image:: img/tutorial_user_palette.svg.png
   :alt:   Combined bar / line chart with non default palette

You can find a complete list of the available palettes in the class tree.

Modifying a palette
-------------------

In the last example, we assigned a palette object to the palette property of
the graph. You can of course create and modify the object before assigning it.

.. include:: tutorial/tutorial_modified_palette.php
   :literal:

The palette object is created in line 6 and we overwrite some of its
properties. An overview on all available properties can be found in the class
documentation for the abstract class ezcGraphPalette. In this example we just
set two colors for the automatic colorization of the datasets and three
symbols for datasets.

Since we assign more than two datasets, the first assigned color will be reused
for the third dataset. You can see the usage of the symbols in the legend and
on the line chart. The line chart displays a symbol for each data point if the
symbol is set to something other than ezcGraph::NO_SYMBOL.

.. image:: img/tutorial_modified_palette.svg.png
   :alt:   Combined bar / line chart with modified palette

Creating a custom palette
-------------------------

To style the graphs to fit a custom look, such as a corporate identity, the
easiest way is to create your own palette.
To create a custom palette you can either extend one of the predefined palettes and
overwrite their properties or extend the abstract palette class.

.. include:: tutorial/tutorial_custom_palette_palette.php
   :literal:

Each undefined color will default to a transparent white. As you
can see in the example definition, you can define alpha values beside the
normal RGB values for the colors. After creating a custom palette, you can use
it like any predefined palette, as previously explained.

.. include:: tutorial/tutorial_custom_palette.php
   :literal:

The example now uses the custom palette to format the output. You can include
palettes using your application's autoload mechanism or require them as
shown in the example above.

.. image:: img/tutorial_custom_palette.svg.png
   :alt:   Combined bar / line chart with custom palette

Chart elements
==============

The chart elements all extend ezcGraphChartElement. Each of the elements can be
configured independently. A default chart consists of the following elements:

- title
- background
- legend
- xAxis
- yAxis

The palette defines the default formatting of the elements. Not only can you set
foreground and background colors for all the elements, but you can also
define their position in the chart or prevent them from being rendered at
all.

Font configuration
------------------

We try to fulfill two goals regarding font configuration. First, there should
be a single point to configure the fonts used for the text areas in the chart.
On the other hand, it should be possible to configure the fonts independently
for each chart element.

The solution is that you can modify the global font configuration by
accessing $graph->options->font. This takes effect on all chart elements
unless you intentionally access the font configuration of an individual chart
element. The following example shows how this works.

.. include:: tutorial/tutorial_chart_font_configuration.php
   :literal:

The output of the example shows, that all texts are using a serif font, while
the title still stays with the default sans-serif font.

.. image:: img/tutorial_chart_font_configuration.svg.png
   :alt:   Font configuration in pie chart

The chart title
---------------

The chart title element will only be rendered if you manually assign a title.
It can be placed on top or at the bottom of the chart.

.. include:: tutorial/tutorial_chart_title.php
   :literal:

The chart title is the simplest element. In line 9, we change the global font
configuration to use a serif font. In the SVG renderer, only the font name is
relevant, because it is up to the client to actually render the bitmap from the
defined vector definitions.

In line 11, we access the font configuration of the title element and change it
back to use a sans-serif font. From now on, no change on the global font
configuration will affect the title's font configuration. In line 14, we set a
maximum font size, which now only affects the legend and the pie chart
captions.

Aside from the font configuration, we set an option for all chart
elements in line 11 - the background color of the current element. This
results in a gray background for the title element only.

.. image:: img/tutorial_chart_title.svg.png
   :alt:   Font and title configuration in pie chart

The background element
----------------------

With all drivers, you can set background images with the option to repeat them
in the same way as in CSS definitions.

.. include:: tutorial/tutorial_chart_background.php
   :literal:

In line 17, we set a background image, and define its position in line 18. You
can use every combination of bottom / center / top with left / middle / right
here, and it defaults to center | middle. In line 19, you set the type
of repetition of the background image. This can be ezcGraph::NO_REPEAT or a
combination of ezcGraph::HORIZONTAL and ezcGraph::VERTICAL. In this case, we
just want a logo to be placed at the bottom right corner of the image.

With the SVG driver, the image is inlined using a data URL with the base64 
encoded content of the binary image file. Using this driver, you do not need to
worry about the locations of your referenced images.

With the GD driver, super sampling is not applied to the images, as this would
make them blurry.

.. image:: img/tutorial_chart_background.svg.png
   :alt:   Pie chart with logo in background

Of course, you could also apply the following settings to the background
element: background color, borders, margins and padding.

The legend
----------

The legend is shown by default and is automatically generated from the assigned
data. If you want to disable the legend, you can do this by setting
it to "false" (line 9).

.. include:: tutorial/tutorial_chart_legend.php
   :literal:

.. image:: img/tutorial_chart_legend.svg.png
   :alt:   Pie chart without legend

Legend configuration options
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Other than hiding the legend, you can also place it at the bottom, left or top
in the chart; you can assign a title for the legend and change the symbol
sizes; you can additionally set the legend size.

.. include:: tutorial/tutorial_legend_options.php
   :literal:

To place the legend at another position on the graph, set the position
property of the legend, as shown in line 17. If the legend is placed at the top or
bottom, it will automatically use a landscape format. The space consumed by the
legend is configured by the landscapeSize setting for landscape-oriented legends
and the portraitSize setting otherwise. The assigned value is the percent
portion of space taken up by the legend, relative to the size of the chart. The
legend only displays a title if you manually set it, as shown in line 19.

.. image:: img/tutorial_legend_options.svg.png
   :alt:   Legend configuration example

Axis
----

The axis defines the unit scale in line and bar charts. There are always two
axes - the x-axis and the y-axis, whose ranges are automatically 
received from the datasets and scaled to display appropriate values.

There are different types of values to display for both the x-axis and the
y-axis. ezcGraph supports different axis types for different types of data. For
normal string keys, the standard labeled axis is usually the right choice. The
numeric axis is predestined to display numeric data, and the date time axis is
for data associated with dates or times. All of the axis types can be assigned
to either axis.

Labeled axes
~~~~~~~~~~~~

The labeled axis is default for the x-axis in both bar and line charts. It
is intended to display string labels of datasets and uses the centered label
renderer by default. You saw it in all the earlier examples with bar
and line charts, but it can be used for both axes as well.

.. include:: tutorial/tutorial_axis_labeled.php
   :literal:

You could argue whether such a chart is really useful - but it works. Instead of
using numeric values, colors are assigned when creating the dataset. The
labeled axis uses the values in the order they are assigned. Line 11 is
the first time we actually configure the axis label renderer. The axis label 
renderer describes how the labels are placed on the axis - the labeled axis 
uses the centered axis label renderer by default, which places the labels 
centered next to the steps on the axis. The setting in line 11 forces the 
renderer to show the zero value, even though it interferes with the axis.

.. image:: img/tutorial_axis_labeled.svg.png
   :alt:   Two labeled axes

Numeric axis
~~~~~~~~~~~~

The numeric axis is the default for the y-axis. It displays
numeric data and automatically determines appropriate scaling for the assigned
values. However, you can also configure all scaling parameters manually.

.. include:: tutorial/tutorial_axis_numeric.php
   :literal:

In this example, we force both axes to be numeric axes in line 10. In lines
12 to 15, we manually set the scaling options for the x-axis. We do not set a
minorStep size here, so it will be automatically calculated from the other
values, as will the settings for the y-axis. Then, we create some random data
and create two datasets from it as usual.

.. image:: img/tutorial_axis_numeric.svg.png
   :alt:   Two numeric axes with random data

The example shows one advantage of a numeric axis over a labeled axis for numeric
data. The axes are moved away from the chart's border to display the negative
values below and left of the axis.

Date time axis
~~~~~~~~~~~~~~

Previously in this tutorial, we used a labeled axis for date time data on the
x-axis in the Wikipedia examples. This works fine for evenly-distributed
time spans. For other data, you should use the date time axis.

.. include:: tutorial/tutorial_axis_datetime.php
   :literal:

You can use timestamps or date time strings as dataset keys. The strings will
be converted using PHP's strtotime() function. 

.. image:: img/tutorial_axis_datetime.svg.png
   :alt:   Date axis example

Axis label renderer
~~~~~~~~~~~~~~~~~~~

As mentioned earlier in this tutorial, the axis label renderer defines where a
label is drawn relative to the step on the axis. You already saw examples 
for all available axis label renderers, but here is an overview:

- ezcGraphAxisExactLabelRenderer

  This is the default renderer for the numeric axis. The labels are drawn
  directly below the axis step. This may look strange sometimes, because it
  is not always possible to draw all labels of one axis on one side
  of the step; the last or first label would exceed the available 
  space for the axis, and be rendered on the other side.

- ezcGraphAxisCenteredLabelRenderer

  This renderer is the default for the labeled axis in line charts and draws the
  label centered next to the step. Therefore, this renderer omits the label for
  the initial step on the axis (0, 0) by default. However, this can be forced
  as shown in the example in `Axis`_ -> `Labeled axes`_. The label is omitted
  because it would interfere with the axis or the labels of the other axis, and
  thus be difficult to read.

- ezcGraphAxisBoxedLabelRenderer

  This is the default renderer for the labeled axis in bar charts. The steps
  on the axis and the grid are not drawn at the position of the label, but
  between two labels. This helps to recognize which bars belong together.
  Labels are rendered centered between two steps on the axis.

Rotated labels on axis
~~~~~~~~~~~~~~~~~~~~~~

There is one more new axis label renderer since version 1.1 of ezcGraph -
ezcGraphAxisRotatedLabelRenderer, which enables you to render rotated labels on
an axis.

.. include:: tutorial/tutorial_rotated_labels.php
   :literal:

In line 9, a custom renderer is defined for the labeled x axis. You can
assign custom axis label renderers on the property $axisLabelRenderer for
ezcGraphChartElementAxis objects.

The renderer used in this example has custom properties like the rotation of
the labels, which is set in degrees, while the rotation direction depends on
the direction of the axis.

It makes sense to define more vertical space below the axis for the
rotated labels as done in line 11 of the above example.

.. image:: img/tutorial_rotated_labels.svg.png
   :alt:   Date axis example

The results conatins rotated labels, which enables you to pack a lot more
labels on one axis.

Additional axis & markers
-------------------------

Aside from the x axis and the y axis, you can add additional axes and markers to one
chart. You can also assign these additional axes to datasets, so that some
datasets use different axes than others.

Add markers to chart
~~~~~~~~~~~~~~~~~~~~

First, add some markers, which only get a label and reside at some
user defined position, to a chart. You may use them to display data boundings
on the y axis, or important values on the x axis.

.. include:: tutorial/tutorial_line_chart_markers.php
   :literal:

You can see a standard line chart, like in the examples before, using the
Wikipedia datasets. In line 15 we add another axis, and configure this one in
the following lines. The position of an axis defines its origin. The
position ezcGraph::LEFT means that the axis starts at the left side of the
graph. You can also use ezcGraph::RIGHT to make the axis start on the right.

The position of the axis may be defined by a float value, which defines the
fractional position in the chart, calculated from the top left position. After
this we also define a label for the axis.

.. image:: img/tutorial_line_chart_markers.svg.png
   :alt:   Line chart with marker

Additional axes
~~~~~~~~~~~~~~~

As previously noted, you can not only add additional axis to one chart, but you can
also assign datasets to use one of these new axes. This will cause the
axis to calculate its values depending on the assigned datasets and the data to
orientate at the new axis.

The new axis may also be of a completely different type than the original chart
axis.

.. include:: tutorial/tutorial_line_chart_additional_axis.php
   :literal:

In this chart we use a different axis, positioned at the very end of the chart,
for the Norwegian Wikipedia data. Due to the different scaling for the English
and Norwegian data, you can easily see that the development of articles is very
similar, on a completely different level.

To use the axis with some dataset, you need to assign the newly created axis to
one of the existing axis properties and to the dataset. In this case we use the $yAxis
property.

.. image:: img/tutorial_line_chart_additional_axis.svg.png
   :alt:   Line chart with additional axis

Datasets
========

Datasets receive user data and provide an interface for
ezcGraph to access this data.

Array data
----------

The array dataset was used for all examples until now, because it is the
simplest way to provide data for ezcGraph.

Average polynomial dataset
--------------------------

The average polynomial dataset uses an existing dataset with numeric keys and
builds a polynomial that interpolates the data points in the given dataset using the
least squares algorithm.

.. include:: tutorial/tutorial_dataset_average.php
   :literal:

Here we use two numeric axes, because we only display numeric data in this
example. First, we create a normal array dataset from some randomly generated
data in line 14. We assign this dataset to the chart to see how well the 
polynomial fits the random data points.

In line 20, we create a ezcGraphDataSetAveragePolynom dataset from the random
data with a maximum polynomial degree of 3 (which is also the default
value). You can directly access the polynomial when we add the dataset to the
graph. The string representation of the polynomial itself is also used as the
name of the dataset.

.. image:: img/tutorial_dataset_average.svg.png
   :alt:   Average polynomial example

For the computation of the polynomial, an equation has to be solved where the
size of the matrix is equal to the point count of the used dataset. Be
careful with datasets with large point counts. This could mean that
ezcGraph will consume a lot of memory and processing power.

Numeric dataset
---------------

Numeric datasets are used to represent mathematical functions in your chart.
You can use callbacks to PHP functions, or your own functions or methods to
define the mathematical function used to create the dataset.

.. include:: tutorial/tutorial_dataset_numeric.php
   :literal:

The numeric dataset constructor receives the start and end values for
the function's input and the function itself using PHP's `callback datatype`__. In
this example we create a function on runtime using create_function(), which
returns the name of the created function (which is a valid callback). The
code of the created function in line 16 returns sine values for the input in 
degrees.

__ http://php.net/manual/en/language.pseudo-types.php

The resolution set in line 20 defines the number of steps used to interpolate
the function in your graph. You should not use a number bigger than the width
of your chart.

.. image:: img/tutorial_dataset_numeric.svg.png
   :alt:   Example numeric dataset

Renderer
========

The renderer transforms chart primitives into image primitives. For example, a
pie segment including labels, highlighting and so on will be transformed
into some text strings, circle sectors and symbols to link the text to the
corresponding circle sector.

ezcGraph comes with the default 2D renderer used in all of the above examples
and a 3D renderer that renders the chart elements in a pseudo 3D isometric
manner.

2D renderer
-----------

All examples until now used the default 2D renderer. There are several
renderer-specific options that have not yet been shown.

Bar chart rendering options
~~~~~~~~~~~~~~~~~~~~~~~~~~~

All the options specific to bar charts are available for all
current renderers.

.. include:: tutorial/tutorial_bar_chart_options.php
   :literal:

As the 2D renderer is the default renderer, we do not need to specify it. In
lines 28 and 29, we configure the width used for the bars. The
option barMargin defines the distance between the sets of bars associated to
one value. The barPadding setting in line 29 defines the distance between bars in one
block.

The option dataBorder in line 31 is available for all chart types in all
renderers and defines the transparency used to draw darkened borders around
bars or pie segments. In this case, we do not draw any borders.

.. image:: img/tutorial_bar_chart_options.svg.png
   :alt:   Bar chart rendering options

Pie chart rendering options
~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. include:: tutorial/tutorial_pie_chart_options.php
   :literal:

One of the pie chart specific options is moveOut in line 21, which defines how
much space in the pie chart is used to move the pie chart segments out from the
center when highlighted. The pieChartOffset setting in line 23 defines the
initial angle for the pie chart segments, which enables you to rotate the pie chart.

In lines 25 to 27, a gleam on the pie chart is defined, with a transparency
value in line 25 (which disables the gleam when set to 0), a color in line 26
and the distance from the outer border of the pie chart in line 27.

In line 29 and 30, a shadow with custom offset and color is added to the pie
chart.

.. image:: img/tutorial_pie_chart_options.svg.png
   :alt:   Pie chart rendering options

Pimp my chart
~~~~~~~~~~~~~

.. include:: tutorial/tutorial_pie_chart_pimped.php
   :literal:

Aside from the gleam added in the last example, you can define a
gleam for the legend symbols. In line 32, the transparency of the gleam is
defined, followed by the size of the gleam. The gleam works for all symbol
types except the circle, where a gleam is not appropriate. The size setting
defines the size of the gleam as a percentage of the symbol size. In the last step in
line 34, the gleam color is defined.

.. image:: img/tutorial_pie_chart_pimped.svg.png
   :alt:   Pimped 2D pie chart

3D renderer
-----------

The three-dimensional renderer can render all charts that the 2D
renderer can do, and uses all the drivers that the 2D renderer uses. The only
difference is that it generates isometric three-dimensional views on the data
instead of simple two-dimensional views.

.. include:: tutorial/tutorial_renderer_3d.php
   :literal:

This examples uses the same code as the first example, except for the renderer
in line 17. You can use the 3D renderer with all of the above examples by
adding this single line.

.. image:: img/tutorial_renderer_3d.svg.png
   :alt:   Simple 3d pie chart

3D pie charts
~~~~~~~~~~~~~

The options in the 2D renderer example still work, and we extend the example
with some 3D renderer-specific options.

.. include:: tutorial/tutorial_pie_chart_3d.php
   :literal:

The pieChartGleamBorder option was removed, because it looks a bit strange on
3D pie charts, although it would still work. In lines 37 and 38, there are
two new options, which configure the 3D effect of the pie chart. The first one
defines the height of the pie and the second one defines the percent shrinkage
compared to the maximum possible vertical size of the pie chart.

.. image:: img/tutorial_pie_chart_3d.svg.png
   :alt:   Pimped 3D pie chart

3D bar charts
~~~~~~~~~~~~~

3D bar charts use the symbol of the dataset as the basic shape for the
rendered bar, so that you can render cylinders or cuboids in your charts.

.. include:: tutorial/tutorial_bar_chart_3d.php
   :literal:

The symbols for these examples are set as described earlier in this tutorial.
Two single options are set to improve the displayed image. legendSymbolGleam is
activated with the default color, and barChartGleam is activated to get more
beautiful bars. You could optionally darken the tops and sides of the bars using the
options barDarkenSide and barDarkenTop.

.. image:: img/tutorial_bar_chart_3d.svg.png
   :alt:   Pimped 3D bar chart

3D line charts
~~~~~~~~~~~~~~

The line chart example with the 3D renderer is again quite simple. It reuses the
example with the statistical data and the approximated polygon.

.. include:: tutorial/tutorial_line_chart_3d.php
   :literal:

Again, the only thing that has changed is the use of the 3D renderer and the
fillLines option (to show that it works for 3D charts as well).

.. image:: img/tutorial_line_chart_3d.svg.png
   :alt: 3D line chart example

Drivers
=======

The driver gets the image primitives from the renderer and creates the final
image. Different drivers can be used depending on
the available extensions and the desired output format.

There are some driver-specific options described below. You can also learn
about them in the API documentation for each driver.

SVG driver
----------

The default driver generates an SVG_ image, a standardized XML vector graphic 
format, which most of the modern browsers can display natively, except for 
Internet Explorer. Even with Internet Explorer, there are several 
plugins available from Corel [1]_, or Adobe [2]_, which enable the browser to 
render SVGs. There are several advantages in using the SVG driver. The XML 
documents can easily be modified later, and compressed effectively. The driver 
is very fast, and all shapes are displayed exactly and anti aliased. You can 
define templates, using an existing SVG document, where the generated chart is
added to a dedicated group; you can then configure all rendering options of the SVG
document. The example below shows such a template created with Inkscape_ and a
simple pie chart rendered using this template.

.. include:: tutorial/tutorial_driver_svg.php
   :literal:

.. image:: img/tutorial_driver_svg.svg.png
   :alt:   SVG driver example with template

.. _SVG: http://www.w3.org/TR/SVG/
.. _Inkscape: http://inkscape.org

The only drawback of SVG is that it is impossible to determine or define the 
exact width of text strings. As a result, the driver can only estimate the size of 
text in the resulting image, which will sometimes fail slightly. Since the
1.3 (2008.1) release you can work around this issue, by using the `Glyph support`_.

.. [1] Abobe SVG plugin: http://www.adobe.com/svg/viewer/install/main.html
.. [2] Corel SVG plugin: http://www.corel.com/servlet/Satellite?pagename=CorelCom/Layout&c=Content_C1&cid=1152796555406&lc=en

Glyph support
~~~~~~~~~~~~~

Since version 1.3 (2008.1) you may set a SVG font to be used by the SVG driver,
which will result in exact text width estimation using glyphs for the chracters
in texts. SVG fonts may be created from TTF fonts using the ttf2svg command
available in the `apache batik`__ package.

__ http://xml.apache.org/batik/

Embedding SVG in HTML
~~~~~~~~~~~~~~~~~~~~~

If you want to embed SVGs in HTML there are several ways to do so. With XHTML
you may inline the content of the SVG in your HTML, as both are just XML. You
need to keep correct namespacing in mind here. Opera and Firefox will support
this technique.

Another way to reference SVGs in your HTML markup, is to use the object
element like following example shows.

::

	<object data="path/to/image.svg" type="image/svg+xml">
		You need a browser capeable of SVG to display this image.
	</object>

You can optionally specify the width and height as attributes in the options
element. With this standards-conforming method, the drawback is that
Microsoft Internet Explorer does not support this. With browsers from the 
Internet Explorer series, you can use the proprietary embed element.

::

	<embed src="path/to/image.svg"></embed>

You cannot specify an alternative text here, and this will not work with
Opera and Firefox. If you need to support all browsers, you can use one of the 
common switches to distinguish between browsers.

::

	<!--[if IE]>
		<embed ... />
	<![endif]-->
	<![if !IE]-->
		<object ... />
	<![endif]-->

Another alternative for embedding SVGs in your HTML would be to use iframes.

GD driver
---------

The GD driver is one of the choices for generating bitmap images. It supports
different font types, if available in your PHP installation, like True Type
Fonts (using the FreeType 2 library or native TTF support) and PostScript Type
1 fonts. We use super sampling to enable basic anti aliasing in the GD driver,
where the image is rendered twice as big and resized back to the requested
size. This is used for all image primitives except text and images.

There are some drawbacks in the GD library that we have not been able to
overcome:

- Transparent pie segments look very strange with GD
- There is no native support for gradients in GD
- Font anti aliasing depends on the font extension. Use the FreeType 2
  library if available, which is the default behavior.

There are some special configuration options for the GD driver. You can
specify the super sampling rate used, and use different output formats (if
available with your bundled GD extension) as shown in lines 13 to 15 in the
following example.

.. include:: tutorial/tutorial_driver_gd.php
   :literal:

.. image:: img/tutorial_driver_gd.jpg
   :alt:   GD driver example jpeg


Element references
==================

Description
-----------

Element references describe a mechanism to modify and reference certain
chart elements to add links, menus or other interactive features in your 
application. The type of the references depend on the driver you use to render
charts. The GD driver will return points describing polygons, so that you can
generate image maps from the data, while the SVG driver will return the IDs of
XML elements.

Element references are created in the renderer. This way it is also possible to
reference legend symbols and text, data labels and of course the actual data
elements.

In ezcGraph version 1.1 and later, you can define URLs for datasets and data
points that will be used when linking the elements. You now can use the function
provided in ezcGraphTools to create the image maps and add links into SVG
images.

SVG example
-----------

.. include:: tutorial/tutorial_reference_svg.php
   :literal:

In ezcGraph version 1.1 and later, you can optionally set a custom cursor type used by the
browser to indicate that you can click on a surface. The cursor defaults to a
pointer normally used for links. You also need to assign
URLs to the datasets or data points, as in the lines 17 and 18, and then
call ezcGraphTools::linkSvgElements (line 23) to modify your SVG. The
result will be a clickable `SVG image`__.

__ img/tutorial_reference_svg.svg

GD example
----------

In the case of GD we want to generate an image map instead of modifying the
generated image. The driver returns polygons described by their edge
coordinates, which you can use to generate an image map.

.. include:: tutorial/tutorial_reference_gd.php
   :literal:

In line 20 we associate a URL to the complete dataset and in line 21 another
URL for the Mozilla data point only. Those URLs will be used to create the
image map in line 31. In the second parameter on line 31 we can
provide a name for the image map, which should be used to associate the image
map to the image in line 37. The result is a `linked legend and linked
pie chart in your generated bitmap`__.

__ img/tutorial_reference_gd.html

SVG to bitmap conversion
------------------------

If you want to benefit from the more beautiful SVG output you can convert the
vector graphics to a bitmap format, like PNG or JPEG, on the server side.
There are several tools than can do this, but for each you need to be able
to execute commands using the exec() function family.

- librsvg
  Small memory footprint and advanced SVG support, including filters (which
  are not used by ezcGraph, though). Example command to convert an image:

  ::

  	rsvg input.svg output.png

- ImageMagick
  Installed on most servers, but has some issues with transparent
  backgrounds in SVG documents. Example command with ImageMagick:

  ::

  	convert -background none input.svg output.png

- Inkscape
  Not available on most servers, but perfect for modifying SVG documents on
  Unix and Windows. Requires X to install, but can be run on CLI, too:

  ::

  	inkscape input.svg -e output.png

All three converters can also export to PDF or postscript, and resize the
document if desired. For further details, please read the documentation of the
respective tool.

Direct output
=============

By default, a graph is rendered to a file, as you normally want to cache
generated images. ezcGraph also provides a method for the direct output of
generated charts. Use this with caution.

The ezcGraph::renderToOutput() method sends the correct Content-Type header
for the selected output driver and writes the chart's image data directly to
output. Do not output anything before using this method.

.. include:: tutorial/tutorial_output.php
   :literal:

This example renders the first graph of this tutorial.

More information
================

For more information, see the ezcGraph API documentation.


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