Image - Blur

There are two blur classes: agg::stack_blur and agg::recursive_blur. agg::stack_blur is 3x-5x faster and has a bit limitations, while agg::recursive_blur is a true Gaussian blur. The interface is the same for these two blurs.

agg::stack_blur<agg::rgba8, agg::stack_blur_calc_rgba<> > blur;
blur.blur (pixFmt, radius);

agg::recursive_blur<agg::rgba8, agg::recursive_blur_calc_rgba<> > blur;
blur.blur (pixFmt, radius);

The radius is roughly equivalent to twice the value of SVG's stdDeviation.

Note that the entire pixFmt is blurred. However, it is pretty straightforward to limit blurring to a specifc region of pixFmt.

template<class PixFormat, class BlurType>
void
blurImage(PixFormat& pixFmt, int x, int y, int width, int height, BlurType& blur, double radius)
{
    agg::rendering_buffer   renBuffer;
    PixFormat subPixFmt (renBuffer);
    subPixFmt.attach (pixFmt, x, y , x + width - 1, y + height - 1);
    blur.blur (subPixFmt, radius);
}

Example

tutorial_blur.cpp does the following.

1. Just the image icon by itself.
2. The image icon blurred using agg::stack_blur
3. The image icon blurred using agg::recursive_blur
4. The image icon blurred using agg::recursive_blur with dx = 5 and dy = 5. Then original image icon was drawn on top. Effectively it creates a shadow effect.

The resulting image is the following.

An equivalent SVG is