Re: Rasterizer clipping

> Hi Petr,
>
> I flipped your functions, because I need to discuss them in reverted
> order... :-)
>
>> void RasterPainterDevice::_renderPath(const Path& path, bool stroke) {
>>   AggPath aggPath(path);
>>   ConvCurve curvesPath(aggPath);
>>
>>   _ras.reset();
>>   _ras.filling_rule(static_cast<agg::filling_rule_e>(_fillMode));
>>   _ras.clip_box(
>>     (double)_clipBox.x1(),
>>     (double)_clipBox.y1(),
>>     (double)_clipBox.x2()-0.000001,
>>     (double)_clipBox.y2()-0.000001);
> [...]
>
> If your _clipBox is in pixel indices, ie. x1() refers to the index of the
> left pixel and x2() refers to the index of the right pixel, then it needs
> to be like this:
>
>   _ras.clip_box(
>     (double)_clipBox.x1(),
>     (double)_clipBox.y1(),
>     (double)_clipBox.x2() + 1,
>     (double)_clipBox.y2() + 1);
>
> That's because the rasterizer clipping is still at a "geometry level". If
> your clipBox can be non-integer, but you still want pixel based clipping,
> then it needs to be like this:
>
>   _ras.clip_box(
>     floor(_clipBox.x1()),
>     floor(_clipBox.y1(),
>     ceil(_clipBox.x2()),
>     ceil(_clipBox.y2()));
>
> In any case, you need to include the pixels at the last colum/row by
> rounding up or adding "+ 1" for integer based pixel indices clipping boxen.
>
>
>
>> 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());
>>
>>   // TODO: Not needed ?
>>   // int extx1 = painter_d->_realRegion.extents().x1();
>>   // int exty1 = d->_clipBox.y1();
>>   // int extx2 = painter_d->_realRegion.extents().x2();
>>   // 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();
>>
>>       sysint_t y = sl.y();
>>
>>       // TODO: Not needed ?
>>       // Vertical clipping to extents.
>>       // 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;
>>       }
>>     }
>>   }
>> }
>
> Since you are doing your own rendering, I suspect that the error is
> somewhere there. I am not 100% sure that if you setup rasterizer clipping,
> that it will never render outside that box. I think it doesn't, but it
> would be thinkable that it still touches outside pixels with cover of 0.
> But I find that highly unlikely. At least I have never seen any problems in
> this regard, but I also usually setup clipping on the renderer as well. In
> your place, I would simply add the necessary debugging facilities to make
> sure of this. My first suspicion would be that the out of bounds access
> happens somewhere in your code. Possibly the fillSpan routines.
>
> Best regards,
> -Stephan
>
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