Lines are approximated by a series of pixels that must lie at display coordinates. They can therefore appear jagged, especially nearly horizontal or nearly vertical lines. This jaggedness is called aliasing. Antialiasing is the smoothing of lines and curves. It reduces the jagged, stair-step appearance of any line that is not exactly horizontal or vertical. emWin supports different antialiasing qualities, antialiased fonts and high-resolution coordinates.
Antialiasing smoothes curves and diagonal lines by "blending" the background color with that of the foreground. The higher the number of shades used between background and foreground colors, the better the antialiasing result (and the longer the computation time).
The quality of antialiasing can be set with a factor between 1 and 6, where 1 means no antialiasing and 6 the highest quality. For most applications factor 4 is sufficient and is a good compromise between quality and performance.
Fonts are available with two levels of antialiasing, low-quality (2bpp) and high-quality (4bpp). The following table shows the effect on drawing the character C without antialiasing and with both types of antialiased fonts.
Antialiased fonts can be created using the Font Converter. The general purpose of using antialiased fonts is to improve the appearance of text. While the effect of using high-quality antialiasing will be visually more pleasing than low-quality antialiasing, computation time and memory consumption will increase proportionally. Low-quality (2bpp) fonts require twice the memory of non-antialiased (1bpp) fonts; high-quality (4bpp) fonts require four times the memory.
|Font type||Black on white||White on black|
Standard (no antialiasing)
2 bpp, 4 shades
4 bpp, 16 shades
When drawing items using antialiasing, the same coordinates are used as for regular (non-antialiasing) drawing routines. This is the default mode. It is not required to consider the antialiasing factor in the function arguments. An antialiased line from (50, 100) to (100, 50) would be drawn with the following function call:
GUI_AA_DrawLine(50, 100, 100, 50);
The high-resolution feature of emWin lets you use the virtual space determined by the antialiasing factor and your display size. The advantage of using high-resolution coordinates is that items can be placed not only at physical positions of your display but also "between" them.
The virtual space of a high-resolution pixel is illustrated beneath based on an antialiasing factor of 3:
To draw a line from pixel (50, 100) to (100, 50) in high-resolution mode with antialiasing factor 3, one would write:
GUI_AA_DrawLine(150, 300, 300, 150);
High-resolution coordinates must be enabled with the routine GUI_AA_EnableHiRes(), and may be disabled with GUI_AA_DisableHiRes(). Both functions are explained later in the chapter. For example programs using the high-resolution feature, see the examples at the end of the chapter.