surface clipping

[Steven J Abner]

  I'm at a point where I could use expert knowledge of surfaces, and 
maybe operators. I'm having to clip surfaces for configuration of 
drawing ports, or some could call them layers, containers, windows, etc.
  The cairo_clip() works within a surface, but doesn't apply the a 
surface inside the cairo_clip() surface. Say you have a surface inside 
a main surface, cairo_xcb_surface_create() for main, then 
cairo_surface_create_for_rectangle() for
a 'drawing port' within the main. This 'drawing port' will act and 
behave like a window inside our main window. This 'sub-port' can be 
grabbed for resize, just like a window, sidebar, 'paned' areas. Now 
when you 'grab' to resize, any 'sub-ports' within the sub-port have to 
be sized/position just as a window would. The resize of the sub-ports 
are determined by whether it shrinks/grows or moves, given on what a 
user wants to do with the sub-ports.
  That's the concept, for the issue, is there an operator that handles 
this or is it up to the programmer to calculate clipping of surfaces?
  I am providing the clipping code and pics hoping that one may gleam 
what I'm trying to do.

        /* clipping code to clip surfaces */
      PhxInterface *mount = nexus->i_mount;
      if (mount != master_iface) {
        PhxRectangle mbox = mount->mete_box;
        int16_t wD, hD, xD, yD;
        wD = (mbox.w < nexus->draw_box.w) ? (mbox.w - 
nexus->draw_box.w) : 0;
        hD = (mbox.h < nexus->draw_box.h) ? (mbox.h - 
nexus->draw_box.h) : 0;
        if (nexus->type == PHX_NFUSE) {
          xD = (nexus->mete_box.x < 0) ? nexus->mete_box.x : 0;
          yD = (nexus->mete_box.y < 0) ? nexus->mete_box.y : 0;
        } else if (nexus->type == PHX_NEXUS) {
          xD = ((nexus->mete_box.x + mbox.x) < 0)
                ? nexus->mete_box.x + mbox.x : 0;
          yD = ((nexus->mete_box.y + mbox.y) < 0)
                ? nexus->mete_box.y + mbox.y : 0;
        }
        if ((xD | yD | wD | hD) != 0) {
          mbox = nexus->draw_box;
          if ( ((mbox.w + xD) < 0) || ((mbox.h + yD) < 0) ) {
            cairo_destroy(cr);
            continue;
          }
          cairo_rectangle(cr, mbox.x - xD - wD,
                              mbox.y - yD - hD,
                              mbox.w + xD,
                              mbox.h + yD);
          cairo_clip(cr);
        }
      }
        /* end clipping code */
  In the pics, the 4 dots per surface are to show corner positions to 
make sure clips are as expected.
Steve

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