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Archive for September, 2009

Shiva generator, krita and metaball

24 September, 2009 1 comment

One of the new thing of the upcoming 2.1 release for Krita (among improved stability) is that the OpenGTL library is now even more integrated, which makes it even easier to write cool filters or generators for Krita.

Today, I will speak about generators. Since Krita 2.0, there is a special kind of layers in Krita: generators, it’s like a normal layer, except that the pixel are generated automatically. In 2.0, the only generator available was a plain color generator. In 2.1, you can write your generator using the Shiva language.


kernel Singleball
{
const float radius = 0.1;
const float ringradius = 0.05;
const float ycenter = 0.5;
const float ycenter = 0.5;
const float2 center = { IMAGE_WIDTH * xcenter, IMAGE_HEIGHT * ycenter };
dependent float pxradius, pxringradius;
void evaluateDependents()
{
int image_size = min(IMAGE_WIDTH, IMAGE_HEIGHT);
pxradius = radius * image_size;
pxringradius = ringradius * image_size;
}
void evaluatePixel(out pixel4 result)
{
float2 vec = result.coord - center;
float angle = atan2( vec.x, vec.y);
float r = length(vec);
if(r (pxradius + pxringradius))
{
result = outsidecolor;
} else {
float v = (r - pxradius) / pxringradius;
result = (1.0 - v) * ballcolor + v * outsidecolor;
}
}
region generated()
{
region reg = { 0, 0, IMAGE_WIDTH, IMAGE_HEIGHT};
return reg;
}
}

The value of the input pixel is computed in evaluatePixel, while evaluateDependents is used to initialize some constants.

The actual version of this kernel can be found here, the full version contains configurable options for the center and radius.

Then to use your generator in krita you just need to copy it to ~/.kde/share/apps/krita/shiva/kernels. As you can see, I have made a metaball generators, integrated in krita, with its option widget:

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