Using Views: Filled Path
The Mosaic class Views::FillPath implements a graphical object specialized to display filled polygons from provided path data. A single path can be composed of line segments, Bézier curves and elliptical arcs. Several paths can be combined together in order to describe complex shapes. This so-called Filled Path view can be used to compose the appearance of a GUI component, in particular to display pie charts, histograms, polygons, circles, etc. The following screenshot demonstrates few examples of how Filled Path views appear in the canvas area of Composer (and accordingly on the screen in your target device):
The following sections are intended to provide you an introduction and useful tips of how to work with the Filled Path view. For the complete reference please see the documentation of the Views::FillPath class.
Add new Filled Path view
To add a new Filled Path view just at the design time of a GUI component do following:
★First ensure that the Templates window is visible.
★In Templates window switch to the folder Views.
★In the folder locate the template Filled Path.
★Drag & Drop the template into the canvas area of the Composer window:
★Eventually name the new added Filled Path view.
Inspect the Filled Path view
This is in so far worth mentioning as all following sections describe diverse features of the Filled Path view by explicitly referring to its corresponding properties. If you are not familiar with the concept of a property and the usage of Inspector window, please read first the preceding chapter Compositing component appearance.
Arrange the Filled Path view
Once added, you can freely move the Filled Path view, or you simply grab one of its corners and resize it in this way. You can control the position and the size of the view also by directly modifying its property Bounds. If you want the Filled Path view to appear behind other views you can reorder it explicitly.
Provide path information for the Filled Path view
In order to display a graphical shape in the Filled Path view, you have to provide the corresponding path information. You can consider the path as a list of connected straight line segments (so-called edges) describing precisely the outline of the shape intended to be to displayed. Depending on the application case the path may consist of few or even hundreds of edges. In this manner you describe primitive (e.g. triangles) or even complex shapes (e.g. circles, rings, Bézier curves or polygons).
To provide the path information you use a Path Data object. Usually you will add such object to your component, you will implement code to fill this object with your particular path information (the lines, arcs, Bézier curves, etc.) and finally you will assign the so prepared object to the property Path of the affected Filled Path view. With the Inspector Assistant you can conveniently select the right object when you edit the initialization expression for the property Path. For example:
As soon as you have connected the both, the information provided in the Path Data object appears within the Filled Path view. If desired, you can assign the same Path Data object to several Filled Path views (and Stroked Path views). If during the runtime of the application, the content of the Path Data object changes, all associated views are updated automatically.
Please note, newly added Filled Path views are using the default Path Data object Resources::DefaultPath describing a simple pie segment. In the practice you will always manage your own path objects containing your particular path information. In any case you should avoid to modify the contents of the Resources::DefaultPath object.
In particular cases, when the desired shape is an ellipse, ring, pie segment, circle segment, etc. you can use the more convenient Arc Path Data object. With this object you don't need to implement any code to prepare the path data. Instead, you simply configure the properties of the Arc Path Data object determining so e.g. the desired radiuses of the ellipse, its start and end angles, and so far.
Determine the origin position for the path coordinates
Per default, the coordinates provided in the associated path object are displayed relative to the top-left corner of the Filled Path view. This corner corresponds thus to the origin of the path own coordinate system (0,0). By modifying the property Offset you can specify other position within the area of the view where to map the origin of this coordinate system. In other words, changing the property Offset causes the displayed shape to be moved within the Filled Path view.
Lets assume, the associated path object describes a circle with its center lying at the origin of the path own coordinate system (0,0). Depending on how the property Offset is configured, the circle appears at different positions within the Filled Path view as demonstrated in the following screenshot. For visualization purpose, the black cross indicates the center of the path coordinate system and the thin blue frames are borders of the respective Filled Path views. Please note, parts of a shape lying outside of the view area are clipped and not visible:
Originally the positive Y-axis of the path coordinate system points downwards, which corresponds to how other positions or coordinates are treated in Embedded Wizard. By initializing the property FlipY with the value true, the Filled Path view mirrors vertically the path coordinate system resulting in the Y-axis pointing upwards, which is more natural for mathematical application cases. The shape described by the path appears accordingly mirrored. Furthermore, with this alternation the effect of the property Offset changes, so that it specifies the position where to map the origin of the path coordinate system relative to the bottom-left corner of the view. The following screenshot demonstrates this effect:
Specify the color of the filled path
To specify the color of the Filled Path view you change its property Color. Alternatively you can configure the view to be filled with a color gradient. For this purpose you specify the colors for the four corners of the view (top-left, top-right, bottom-right and bottom-left) individually by using the corresponding properties ColorTL, ColorTR, ColorBR and ColorBL. The gradient colors are interpolated linearly between the specified values. Using color values with alpha < 255 causes the filled path to appear semi- or even transparent. For example:
Determine the rule how to fill nested path areas
With the property FillRule you specify the algorithm which is used by the Filled Path view during the rasterization process to determine what area of the provided path should appear filled and what area should remain empty. This is in particular essential in case of a complex path, which intersects itself or a path composed of several nested sub-paths. Following are the possible fill rules:
Fills the path areas alternately depending on the nesting level of the enclosed path segments. An area is considered as filled if the number of path segments between a point lying inside the area and any point outside the entire shape is odd. If the number of path segments is even, the area is not filled.
Fills the path areas depending on the nesting level of the enclosed path segments and their winding direction. An area is considered as filled when counting the path segments between a point lying inside the area and any point outside the entire shape the resulting value is not zero, whereby paths with positive winding direction increment the value while paths with negative winding decrement it. If the counter value is 0 (zero), the area is not filled.
The following figures demonstrate the effect of the both fill rules. Please note the small arrows indicating the winding direction of the particular path segment:
Control the quality of the filled path
The Filled Path view rasters the shape per default with enabled anti-aliasing. This produces the best possible results. If not desired, with the property Quality you can disable this mode. For this purpose initialize Quality with the value false. The following figure demonstrates the results depending on the current setting of the property:
Embedded Wizard own implementation to raster vector graphics calculates with 4x anti-aliasing, which means that every pixel is divided in 4 sub-pixel vertically and 4 sub-pixel horizontally. If the vector graphic is rasterized by using target own graphics subsystem (e.g. GPU), the resulting anti-aliasing depends on the implementation of this subsystem. In particular cases (e.g. in case of the WebGL Platform Package) the anti-aliasing can't be deactivated.
Despite the advantages, you should consider, that with enabled anti-aliasing the raster operations are more computing intensive. Thus, if your target device is not powerful nor doesn't provide any dedicated graphics hardware to raster vector graphics, setting the property Quality to the value false may improve the performance.
Use the buffered mode for the Filled Path view
Per default, the Filled Path view rasters the shape every time the screen update is performed and the view lies within the affected screen area. This is true even if the associated path data does not change. Depending on the size of the Filled Path view and the complexity of the path, the rasterization may impact the performance of your application.
With the property Buffered you can instruct the Filled Path view to raster the shape into an internal bitmap and use this bitmap during the screen update instead of rasterizing the path again. For this purpose, initialize the property Buffered with the value true. Please note, this optimization make sense only when the shape (the path data) does not change. When the path data changes with every screen update, activating the buffered mode will not improve the performance since with every alternation of the path data, the shape needs to be rasterized again.
Please consider, that with activating the buffered mode, the Filled Path view reserves memory for an internal bitmap to store the rasterized shape inside. The size of the bitmap corresponds to the actual size of the view. In other words, a 400x200 pixel large Filled Path view will be buffered with a 400x200 pixel large bitmap. Since the bitmap is stored in the ALPHA8 format (1 byte per pixel) the bitmap would occupy ~80 KB of the RAM. Thus, if RAM is a scarce resource in your target device, you should use the buffering mode with prudence.
Control the visibility of the Filled Path view
In the complete GUI application an individual view is visible on the screen only when all of its superior Owner components are visible too, the view itself does lie within the visible area of the superior components and the view is not covered by other sibling views nor components.