> You have to set the MAME "pre-scale" to 1 when HLSL is enabled.
To me it makes more sense to set it to a higher value (my native res is 1280x1024, I set prescale to 3) because you will want a clean and sharp image to be processed by the HLSL effects, not the blurry image you get when prescale is set to 1.
Like the signal an arcade PCB sends to a monitor. The image does not come out "blurry" from an arcade PCB, like it does from MAME with prescale set to 1.