Trapezoids??

The Qt X11 renderer uses trapezoids to render with XRenderCompositeTrapezoids. I am trying to use the code to render with CompositeTags, but all I get is this mishmash of triangles.

XRender defines a trapezoid as

{
A,B,C,D
top, bottom
}

...where A,B,C and D are points (x,y) and top and bottom are floats.

Now my question is this: What role does the top and bottom values play?? As far as I can see, it is enough with four points to define a trapezoid, so why are the top and bottom values needed??

I found



where



This from :
http://www.x.org/archive/X11R7.5/doc/libXrender/libXrender.txt

Is your information correct?

@broadblues

Yes, that's the information I have. Eg. they use fixed point and not floating point, but apart from that I think my description fits.

I might have to write my own triangulator, which is dull, but I would rather that than have to invoke the glu triangulator (trying to get rid of opengl alltogether).

@alfkil

from renderproto.txt (Trapezoids)
Quote:

So my guess would be they are some sort of limitation for the fill operation?

@Gazelle

Yes, I think that is it. Managed to make it work with some copy/pasted code from the OpenGL triangulator .

Alfkil: yeah!