Reading back your suggestion of use a derived class for CairoSurface I
think that it is not a good idea. synfig::Surface has one alpha_pen defined
(and used everywhere) that is a class that is constructed based on Color
class and ColorPrep. ColorPrep is hard coded to use a Color class so at
some point we need to create a CairoColorPrep. Also the blend function are
passed to the alpha_pen to perform the blending of two colors.
Since my idea is to emulate the current Software render using a
CairoSurface (with ARGB 32 bits colors) without use initially any of the
Cairo high level API, it is needed to:
1) Define a CairoColor class. I wanted it to be a template specialization
but it is a bit complex. Also a custom independent CairoColor would be
better since there are some operations that needs to be redefined in any
case at the implementation. For example the sum/subtraction of two colors
needs to check if the color channel has passed the 255 or 0 value to avoid
cycle the value.
2) Based on CairoColor recreate the CairoColorPrep class. ColorAccumulator
is not needed since the USE_HALF directive won't never be used with Cairo.
3) Modify etl::surface to handle the pitch as stride. So set_pitch member
function is needed.
4) Based on CairoColor and CairoColorPrep classes create CairoSurface with
its corresponding CairoAlphaPen based on the current etl::surface and
etl::alpha_pen templates. CairoSurface will have a cairo_surface_t pointer
inside that will be initialized properly. The pointer to data will be get
from the cairo_image_surface_get_data () and passed to surface at creation
time.
5) Define the blend methods using a template function like this (one
example):
template <class C>
static C blendfunc_ALPHA_DARKEN(C &a,C &b,float amount)
{
if(a.get_a()*amount > b.get_a())
return a.set_a(a.get_a()*amount);
return b;
}
So I can reproduce the blend methods using a CairoColor instead.
Once the emulation is completed, then starts the second stage. Use Cairo
properly when possible as described in the document I posted in google docs.
Cheers!
--
Carlos
http://synfig.org
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