There appears to be a problem drawing 45-degree lines when the stroke is partially transparent. The lines are rasterized with "extra" pixels, producing a heavier line than expected.
The problem does not seem to occur when the stroke is opaque. And it only happens on 45/225-degree "forward slash" lines, not 135/315-degree "backslash" lines.
Quote:
// to demonstrate rasterization problem with lines
// at certain angles when partially transparent
size(200,200);
background(255);
noSmooth(); // is default, but make sure
strokeWeight(1); // is default, but make sure
stroke(0); // reference: all lines rasterize correctly when opaque
line(20,20, 10,10);
line(20,20, 30,10);
line(20,20, 10,30);
line(20,20, 30,30);
stroke(0,192); // exact alpha value doesn't appear to matter, as long as < 255
line(120,20, 110,10); // ok
line(120,20, 130,10); // incorrect staircasing
line(120,20, 110,30); // incorrect staircasing
line(120,20, 130,30); // ok
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inconsistent line rasterization with alpha (Read 1268 times)