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Re: Is it possible to perform this type of rendering?

by Petr Kobalíček :: Rate this Message:

Hi Vinnie,

I don't know if I will help you, but I think that you should study
agg::rasterizer_scanline_aa<> class.

For example I'm doing somethink like this in my library:

// Types
typedef agg::rasterizer_scanline_aa<> Rasterizer;
typedef agg::scanline_p8 ScanlineP8;
typedef agg::scanline_u8 ScanlineU8;

template<int BytesPerPixel, class Rasterizer, class Scanline>
static void FOG_OPTIMIZEDCALL AggRenderScanlines(
RasterPainterDevice* d, Rasterizer& ras, Scanline& sl)
{
if (!ras.rewind_scanlines()) return;

uint8_t* pBase = d->_workRaster;
uint8_t* pRas;
uint8_t* pCur;
sysint_t stride = d->_stride;

sl.reset(ras.min_x(), ras.max_x());

int exty1 = d->_clipBox.y1();
int exty2 = d->_clipBox.y2();

FillSpan fillSpan = d->_fillFuncs.fillSpan;
FillSpanM fillSpanM_A8 = d->_fillFuncs.fillSpanM_A8;

// solid source
if (1)
{
while (ras.sweep_scanline(sl))
{
unsigned num_spans = sl.num_spans();
typename Scanline::const_iterator span = sl.begin();

// TODO: is this necessary?
int y = sl.y();
if (y < exty1) continue;
if (y >= exty2) break;

pRas = pBase + y * stride;

for (;;)
{
int x = span->x;
int len = span->len;

pCur = pRas + Raster::mul<int, BytesPerPixel>(x);

if (len > 0)
{
fillSpanM_A8(pCur, &d->_source, span->covers, (unsigned)len);
}
else
{
len = -len;
FOG_ASSERT(len > 0);

uint32_t cover = (uint32_t)*(span->covers);
if (cover == 0xFF)
{
fillSpan(pCur, &d->_source, len);
}
else
{
uint32_t t = Raster::bytemul(d->_source.i, cover);
fillSpan(pCur, &t, len);
}
}

if (--num_spans == 0) break;
++span;
}
}
}
}

You can see that by calling sweep_scanlines() you will gen spans with
coverage informations and you can do what you want with these spans.
I'm using this way to connect antigrain with BlitJit and the speed is
very promising.

Cheers
- Petr

2009/4/27 Vinnie <thevinn@...>:

>
> Dear Group:
>
> I'm drawing a ton of cool-looking controls, sliders, and knobs with agg. Unfortunately all the gradient fills and anti-aliasing comes at the price of some speed. I want to cache certain un-changing elements into an offscreen bitmap. However, these elements have transparency information associated with them....so...
>
> I would first like to get an idea if what I need to do is possible with agg before I go delving in.
>
> Specifically, I want to create a new renderer (I think thats the component I need to modify) that instead of blending color values into the destination map using the coverage information, writes the color as a solid into the destination map, and stores the coverage information in a separate channel.
>
> In other words, produce the equivalent of a Photoshop Layer (red, green, and blue color planes plus one alpha channel for transparency) based on drawing output.
>
> For example if I draw an anti-aliased circle, I would want as my output to be a pure black circle in the RGB channels, with the coverage information going into the fourth channel (value=255 on the interior, and intermediate values 1-254 along the edge holding the coverage information).
>
> Would I do this by providing my own version of renderer_scanline_aa_solid? Is that the right class?
>
> Or does agg perhaps already have the ability to do this by some magic combination of nesting templates?
>
> Thanks!
>
>
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------------------------------------------------------------------------------
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Check out the new simplified licensign option that enables unlimited
royalty-free distribution of the report engine for externally facing
server and web deployment.
http://p.sf.net/sfu/businessobjects
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