Hi,
Welcome to the forum,
This code works to produce your shape using a similar technique to what you were already using but with a left hand edge strip.
Maybe some other users can improve on it too
Best Regards, BRT Community
CLEAR(1, 1, 1)); // clear screen
COLOR_RGB(255, 100, 0)
STENCIL_OP(INCR,INCR)
COLOR_MASK(0,0,0,0)
BEGIN(EDGE_STRIP_L)
VERTEX2II(30,100,0,0)
VERTEX2II(100,100,0,0)
VERTEX2II(150,150,0,0)
VERTEX2II(150,250,0,0)
VERTEX2II(100,300,0,0)
VERTEX2II(30,300,0,0)
VERTEX2II(80,250,0,0)
VERTEX2II(80,150,0,0)
VERTEX2II(30,100,0,0)
END()
COLOR_MASK(1,1,1,1) )
STENCIL_FUNC(EQUAL, 1, 255)
BEGIN(EDGE_STRIP_L)
VERTEX2II(300,0,0,0)
VERTEX2II(300,300,0,0)
END()
STENCIL_FUNC(ALWAYS,0,255)
LINE_WIDTH(32)
COLOR_RGB(255, 255, 255)
BEGIN(LINE_STRIP)
VERTEX2II(30,100,0,0)
VERTEX2II(100,100,0,0)
VERTEX2II(150,150,0,0)
VERTEX2II(150,250,0,0)
VERTEX2II(100,300,0,0)
VERTEX2II(30,300,0,0)
VERTEX2II(30,300,0,0)
VERTEX2II(80,250,0,0)
VERTEX2II(80,150,0,0)
VERTEX2II(30,100,0,0)
END()
DISPLAY()