Graphics

The Graphics object represents a graphics context through which drawing can take place. A graphics context has a destination, which is either the actual device screen or an off-screen image. Off-screen images are often used to implement double buffering. Graphics objects can be obtained by calling the getGraphics() method. The object of an off-screen image can be held indefinitely by the MIDlet. Graphics objects are positioned on Canvas and are a part of the low-level APIs.

A Graphics object provides a set of methods for rendering drawing primitives: text, images, lines, rectangles, and arcs. It also supports clipping and origin translation methods. A Graphics context has a color associated with it, which it uses when rendering primitives. MIDP supports a 24-bit color model (red, green, and blue have 8 bits each). A device's color characteristics are obtained using the Display object's numColors() method.

The Image class provides several static methods for the creation of images: from a file, from another image, and from a raw byte array. Images are either mutable (editable) or immutable (fixed). An image created from a file is immutable.

Symbian implementation supports all image formats that are supported in the underlying platform (for example, image-handling module). These include:

  • PNG (as mandated by the MIDP 2.1 specifications

  • GIF (including animated GIFs)

  • JPEG (as mandated by the JTWI API specification)

Based on image format capabilities, both simple palette transparency (e.g. TRNs chunk of PNG) and alpha channel based transparency are supported in Symbian.

Image sizes

No hard coded limitations exist on supported image sizes. Many applications tend to use images that may be significantly larger than the size of a screen.

When the MIDlet tries to display an image that does not match the reserved space the following methodology is used to enforce the layout:

  • If the image is smaller than the reserved space, the image is centered in the space.

  • If the image is bigger than the reserved space, the part that fits the area from the top left corner of the image is shown, rest is clipped.

  • Images are not scaled.

Font sizes

MIDP LCDUI Font class provides three different sizes for font: SMALL, MEDIUM, and LARGE. Corresponding pixel sizes vary between different resolutions. In addition to resolution variety, different language variants may have their own restrictions. For example, some variants do not support bold and/or italic fonts. In some cases, small font size can appear equal to medium size.

Note: The pixel size values in 'Font sizes' column refer to the text row height. This value equals to the value returned by Font.getHeight method.

For additional examples, see the following articles at Forum Nokia wiki:

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