.. _plot_renderers: ============== Plot renderers ============== Plot renderers are the classes that actually draw the different kinds of plots, or plot-like elements as for instance color bars. This section describes the concepts that are common to all kind of plots. A separate page contains an exhaustive :ref:`list of all plot types ` defined in Chaco. Common interface ================ The base interface is defined in the abstract class :class:`~chaco.abstract_plot_renderer.AbstractPlotRenderer`, and provides attributes and methods to set size, position, and aspect of the plotting area. Three more specialized interfaces are used by most concrete implementations, namely :class:`~chaco.base_xy_plot.BaseXYPlot`, which is the interface for :ref:`X-vs-Y plots `, :class:`~chaco.base_2d_plot.Base2DPlot`, which is the interface for :ref:`2D plots <2d_plots>` (e.g., :ref:`image plots ` or :ref:`contour plots `) and :class:`~chaco.base_1d_plot.Base1DPlot`, which is the interface for :ref:`1D plots <1d_plots>` (e.g., :ref:`jitter plots ` or :ref:`1D scatter plots `). The base interface inherits from a deep hierarchy of classes generating from the :mod:`enable` package, starting with :class:`enable.coordinate_box.CoordinateBox` (representing a box in screen space) and :class:`enable.interactor.Interactor` (which allows plot components to react to mouse and keyboard events), and down through :class:`enable.component.Component` and :class:`chaco.plot_component.PlotComponent` (follow :ref:`this link for a description of the relationship between Chaco and enable `). The class where most of the functionality is defined is :class:`enable.component.Component`. Here we give a summary of all the important properties exposed in :class:`~chaco.abstract_plot_renderer.AbstractPlotRenderer`, without worrying too much about their origin in the hierarchy. Also, to avoid unnecessary cluttering of the page, attributes and methods that are of secondary importance are not listed. Please refer to the API documentation for more details. Box properties -------------- All plot renderers are :mod:`enable` graphical components, and thus correspond to a rectangular area in screen space. The renderer keeps track of two areas: an inner box that only contains the plot, and an outer box that includes the padding and border area. The properties of the boxes are controlled by these attributes: :attr:`position` Position of the internal box relative to its container, given as a list [x,y]. If there is no container, this is set to [0, 0]. "Absolute" coordinates of point (i.e., relative to top-level parent :class:`Window` object) can be obtained using :attr:`get_absolute_coords(*coords)`. :attr:`x`, :attr:`y`, :attr:`x2`, :attr:`y2` Coordinates of the lower-left (x,y) and upper-right (x2,y2) pixel of the internal box, relative to its container. :attr:`bounds`, :attr:`width`, :attr:`height` Bounds of the internal box, in pixels. :attr:`bounds` is a list [width, height]. :attr:`outer_position`, :attr:`outer_x`, :attr:`outer_y`, :attr:`outer_x2`, :attr:`outer_y2`, :attr:`outer_bounds`, :attr:`outer_width`, :attr:`outer_height`, :meth:`set_outer_position`, :meth:`set_outer_bounds` Attributes for the outer box equivalent to those defined above for the inner box. Modifying the outer position attributes is the right way to move the plot without changing its padding or bounds. Similarly, modifying the outer bounds attributes leaves the lower-left position and the padding unchanged. :attr:`resizable`, :attr:`fixed_preferred_size` String that defines in which dimensions the component is resizable. One of '' (not resizable), 'v' (resizable vertically), 'h' (resizable horizontally), 'hv' (resizable in both directions, default). If the component is resizable, :attr:`fixed_preferred_size` can be used to specify the amount of space that the component would like to get in each dimension, as a tuple (width, height). In this case, width and height have to be understood as relative sized: if one component in a container specifies, say, a fixed preferred width of 50 and another one specifies a fixed preferred width of 100, then the latter component will always be twice as wide as the former. :attr:`aspect_ratio`, :attr:`auto_center` Ratio of the component's width to its height. This is used to maintain a fixed ratio between bounds when thet are changed independently, for example when resizing the window. :attr:`auto_center` specifies if the component should center itself in any space that is left empty (default is True). :attr:`padding_left`, :attr:`padding_right`, :attr:`padding_top`, :attr:`padding_bottom`, :attr:`padding`, :attr:`hpadding`, :attr:`vpadding` Padding space (in pixels). :attr:`padding` is a convenience property that returns a tuple of (left, right, top, bottom) padding. It can also be set to a single integer, in which case all four padding attributes are set to the same value. :attr:`hpadding` and :attr:`vpadding` are read-only properties that return the total amount of horizontal and vertical padding (including the border width if the border is visible). :attr:`get_absolute_coords(*coords)` Transform coordinates relative to this component's origin to "absolute" coordinates, relative to top-level container. Aspect properties ----------------- These attributes control the aspect (e.g. color) of padding, background, and borders: :attr:`bgcolor` The background color of this component (default is white). This can be set to "transparent" or "none" if the component should be see-through. The color can be specified as a string or as an RGB or RGBa tuple. :attr:`fill_padding` If True (default), fill the padding area with the background color. :attr:`border_visible` Determines if the border is visible (default is False). :attr:`border_width` Thickness of the border around the component in pixels (default is 1). :attr:`border_dash` Style of the lines tracing the border. One of 'solid' (default), 'dot dash', 'dash', 'dot', or 'long dash'. :attr:`border_color` Color of the border. The color can be specified as a string or as an RGB or RGBa tuple. .. _plot_layers: Layers ------ Each plot is rendered in a sequence of layers so that different components can plot at different times. For example, a line plot is drawn *before* its legend, but *after* the axes and background grid. The default drawing order is defined in :attr:`~chaco.plot_component.PlotComponent.draw_order` as a list of the names of the layers. The definition of the layers is as follows: 1. **background**: Background image, shading, and borders 2. **image**: A special layer for plots that render as images. This is in a separate layer since these plots must all render before non-image plots 3. **underlay**: Axes and grids 4. **plot**: The main plot area itself 5. **selection**: Selected content are rendered above normal plot elements to make them stand out. This can be disabled by setting :attr:`use_selection` to False (default). 6. **border**: Plot borders 7. **annotation**: Lines and text that are conceptually part of the "plot" but need to be rendered on top of everything else in the plot 8. **overlay**: Legends, selection regions, and other tool-drawn visual elements Concrete plot renderers set their default draw layer in :attr:`~chaco.plot_component.PlotComponent.draw_layer` (default is 'plot'). Note that if this component is placed in a container, in most cases the container's draw order is used, since the container calls each of its contained components for each rendering pass. One can add new elements to a plot by appending them to the :attr:`underlays` or :attr:`overlays` lists. Components in these lists are drawn underneath/above the plots as part of the 'underlay'/'overlay' layers. They also receive mouse and keyboard events. Interaction ----------- Plot renderers also inherit from :class:`enable.interactor.Interactor`, and as such are able to react to keyboard and mouse events. However, interactions are usually defined as tools and overlays. Therefore, this part of the interface is described at those pages. .. TODO: add reference to interaction interface Context ------- Since plot renderers take care of displaying graphics, they keep references to the larger graphical context: :attr:`container` Reference to a container object (None if no container is defined). The renderer defines its position relative to this. :attr:`window` Reference to the top-level enable Window. :attr:`viewports` List of viewport that are viewing this component Screen and Data Mapping ----------------------- All :class:`~chaco.abstract_plot_renderer.AbstractPlotRenderer` subclasses are expected to provide three methods for mapping to and from screen space and data space: .. :py:method:: map_screen(data_array) :map_screen: This is expected to take an array of points (as columns) in the appropriate data coordinates, and return the corresponding points in screen pixel coordinates (measured from the bottom left of the plot component). .. :py:method: map_data(screen_pt) :map_data: This is the reverse of map_screen, and takes an array of points (as columns) screen pixel coordinates relative to the renderer component and return the corresponding points in screen data coordinates. .. :py:method:map_index(screen_pt, threshold=0.0, outside_returns_none=True, index_only=False) :map_index: This method takes a point in screen pixel coordinates and returns an appropriate index value that can be used to index into data. This can be used by hit-testing methods (see below), and provides optional arguments such as threshold distances. Not every renderer implements this, and some data sets may not be amenable to this method, either. Others ------ :attr:`use_backbuffer` If True, the plot renders itself to an offscreen buffer that is cached for later use. If False (default), then the component will *never* render itself back-buffered, even if asked to do so. :meth:`invalidate_and_redraw` Convenience method to invalidate our contents and request redraw. This method is sometimes useful when modifying a Chaco plot in an ipython shell. .. _xy_plots: X-Y Plots interface =================== The class :class:`chaco.base_xy_plot.BaseXYPlot` defines a more concrete interface for X-vs-Y plots. First of all, it handles data sources and data mappers to convert real data into screen coordinates. Second, it defines shortcuts for plot axes, labels and background grids. Data-related traits ------------------- X-Y plots need two sources of data for the X and Y coordinates, and two mappers to map the data coordinates to screen space. The data sources are stored in the attributes :attr:`~chaco.base_xy_plot.BaseXYPlot.index` and :attr:`~chaco.base_xy_plot.BaseXYPlot.value`, and the corresponding mappers in :attr:`~chaco.base_xy_plot.BaseXYPlot.index_mapper` and :attr:`~chaco.base_xy_plot.BaseXYPlot.value_mapper`. 'Index' and 'value' correspond to either the horizontal 'X' coordinates or the vertical 'Y' coordinates depending on the orientation of the plot: for :attr:`~chaco.base_xy_plot.BaseXYPlot.orientation` equal to 'h' (for horizontal, default), indices are on the X-axis, and values on the Y-axis. The opposite is true when :attr:`~chaco.base_xy_plot.BaseXYPlot.orientation` is 'v'. The convenience properties :attr:`~chaco.base_xy_plot.BaseXYPlot.x_mapper` and :attr:`~chaco.base_xy_plot.BaseXYPlot.y_mapper` allow accessing the mappers for the two axes in an orientation-independent way. Finally, the properties :attr:`~chaco.base_xy_plot.BaseXYPlot.index_range` and :attr:`~chaco.base_xy_plot.BaseXYPlot.value_range` give direct access to the data ranges stored in the index and value mappers. Axis, labels, and grids ----------------------- :class:`~chaco.base_xy_plot.BaseXYPlot` defines a few properties that are shortcuts to find axis and grid objects in the :ref:`underlays and overlays layers ` of the plot: :attr:`~chaco.base_xy_plot.BaseXYPlot.hgrid`, :attr:`~chaco.base_xy_plot.BaseXYPlot.vgrid` Look into the underlays and overlays layers (in this order) for a :class:`PlotGrid` object of horizontals / vertical orientation and return it. Return None if none is found. :attr:`~chaco.base_xy_plot.BaseXYPlot.x_axis`, :attr:`~chaco.base_xy_plot.BaseXYPlot.y_axis` Look into the underlays and overlays layers (in this order) for a :class:`PlotAxis` object positioned to the bottom or top, or to the left or right of plot, respectively. Return the axis, or None if none is found. :attr:`~chaco.base_xy_plot.BaseXYPlot.labels` Return a list of all :class:`PlotLabel` objects in the overlays and underlays layers. .. TODO: add links to axis and grid documentation Hittest ------- :class:`~chaco.base_xy_plot.BaseXYPlot` also provides support for "hit tests", i.e., for finding the data point or plot line closest to a given screen coordinate. This is typically used to implement interactive tools, for example to select a plot point with a mouse click. The main functionality is implemented in the method :attr:`hittest(screen_pt, threshold=7.0, return_distance=False)`, which accepts screen coordinates ``(x,y)`` as input argument :attr:`screen_pt` and returns either 1) screen coordinates of the closest point on the plot, or 2) the start and end coordinates of the closest plot line segment, as a tuple ``((x1,y1), (x2,y2))``. Which of the two behaviors is active is controlled by the attribute :attr:`~chaco.base_xy_plot.BaseXYPlot.hittest_type`, which is one of 'point' (default), or 'line'. If the closest point or line is further than :attr:`threshold` pixels away, the methods returns None. Alternatively, users may call the methods :meth:`get_closest_point` and :meth:`get_closest_line`. Others ------ Two more attributes are worth mentioning: :attr:`~chaco.base_xy_plot.BaseXYPlot.bgcolor` This is inherited from the AbstractPlotRenderer interface, but is now set to 'transparent' by default. :attr:`~chaco.base_xy_plot.BaseXYPlot.use_downsampling` If this attribute is True, the plot uses downsampling for faster display (default is False). In other words, the number of display points depends on the plot size and range, and not on the total number of data points available. .. note:: At the moment, only :class:`LinePlot` defines a downsampling function, while other plots raise a :class:`NotImplementedError` when this feature is activated. .. _twod_plots: 2D Plots interface ================== The class :class:`chaco.base_2d_plot.Base2DPlot` is the interface for plots that display data defined on a 2D grid, like for example image and contour plots. Just like its companion interface, :ref:`BaseXYPlot `, it handles data sources and data mappers, along with convenient shortcuts to find axes, labels and grids. Unlike other plot renderers, 2D plots draw on the :ref:`'image' layer `, i.e., above any underlay element. Data-related traits ------------------- 2D plots need two sources of data: one for the coordinates of the 2D grid on which data is displayed, stored in the attribute :attr:`~chaco.base_2d_plot.Base2DPlot.index` (a subclass of :class:`~chaco.grid_data_source.GridDataSource`); and one for the values of the data at each point of the grid, :attr:`~chaco.base_2d_plot.Base2DPlot.value` (a subclass of :class:`~chaco.image_data.ImageData`). The index data source also needs a 2D mapper, :attr:`~chaco.base_2d_plot.Base2DPlot.index_mapper`, to map data coordinates to the screen. The orientation on screen is set by :attr:`~chaco.base_2d_plot.Base2DPlot.orientation` (either 'h' -- the default -- or 'v'), which controls which of the two coordinates defined in :attr:`~chaco.base_2d_plot.Base2DPlot.index` is mapped to the X axis. It is possible to access a mapper for the coordinates corresponding to the individual screen coordinates independently of orientation using the properties :attr:`~chaco.base_2d_plot.Base2DPlot.x_mapper` and :attr:`~chaco.base_2d_plot.Base2DPlot.y_mapper`. Finally, :attr:`~chaco.base_2d_plot.Base2DPlot.index_range` is a shortcut to the 2D range of the grid data. Others ------ The attribute :attr:`~chaco.base_2d_plot.Base2DPlot.alpha` defines the global transparency value for the whole plot. It ranges from 0.0 for transparent to 1.0 (default) for full intensity. .. _1d_plots: 1D Plots Interface ================== The class :class:`chaco.base_1d_plot.Base1DPlot` defines a more concrete interface for plots that plot their data along one axis, either horizontal or vertical. Like the other base plot classes it handles data sources and data mappers to convert real data into screen coordinates, but unlike the other classes it doesn't define shortcuts for plot axes, labels and background grids. These decorations should either be provided directly when creating the plot, if they are desired, or provided by plot containers like the :class:`chaco.data_view.DataView` or :class:`chaco.plot.Plot` classes. Data-related traits ------------------- 1D plots need one source of data and one mapper to map coordinates to screen space. The data source is stored in the attribute :attr:`~chaco.base_1d_plot.Base1DPlot.index` and the corresponding mapper is :attr:`~chaco.base_1d_plot.Base1DPlot.index_mapper`. The 'index' corresponds to either the horizontal 'X' coordinates or the vertical 'Y' coordinates depending on the orientation of the plot: for :attr:`~chaco.base_1d_plot.Base1DPlot.orientation` equal to 'h' (for horizontal), indices are on the X-axis, and values on the Y-axis. The opposite is true when :attr:`~chaco.base_xy_plot.base_1d_plot.orientation` is 'v' (the default). The convenience properties :attr:`~chaco.base_1d_plot.Base1DPlot.x_mapper` and :attr:`~chaco.base_1d_plot.Base1DPlot.y_mapper` allow accessing the mappers for the two axes in an orientation-independent way. The properties take the value ``None`` for the off-orientation case (ie. :attr:`~chaco.base_1d_plot.Base1DPlot.x_mapper` is ``None`` for vertical orientation and :attr:`~chaco.base_1d_plot.Base1DPlot.y_mapper` is ``None`` for horizontal orientation). Finally, the property :attr:`~chaco.base_1d_plot.Base1DPlot.index_range` gives direct access to the data ranges stored in the index and value mappers.