With regards to the half pixel offset possibly being the culprit in single line mode; looking at the corsair tekst in single line mode enlarged (fourth picture in
post #60 ), it seems that it may be interpolated / sampled just between the lines. I.e. the vertical white stripes of the letters seem correct, but the
horizontal white pixels / lines in the "corsair" text are all grey.
Is the input to the shader by any chance an odd number of lines in single line mode, but an even number of lines in double-line-mode? Just guessing as to what is happening in single line mode, and why it seems to be correct in double line mode..