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You might occasionally notice thin lines between parts when checking rendered exports or the Render view, yet they aren’t visible in OpenGL. This is due to anti-aliasing and can occur because of certain cutting techniques.
What is aliasing and anti-aliasing?
Aliasing appears as a jagged edge on digital graphics, caused by the display’s attempt to process shapes. This happens due to screen resolution and the nature of the pixels displayed.
When you render a scene in Harmony, anti-aliasing is automatically applied to smooth out the jagged edges created by aliasing. This is done by creating a soft transition between the pixel colours on the edge of adjacent shapes, which results in smoother visuals.
Why does the line appear?
The thin line seen between artwork in the Render view is caused by the anti-aliasing effect when artwork is cut right up to the edge of another shape.
When anti-aliasing is applied, it chooses which of the two surrounding colours to read when filling in the gap. This often gives the appearance of a thin line from the layer connected to the matte port of the cutter.
So essentially, these lines are created by a combination of cutting techniques and anti-aliasing. These techniques are explained below.
Invert cutting with an Auto-Patch
Using an Auto-Patch node to invert-cut a layer will create this issue due to the nature of the Auto-Patch and how it uses Art layers. See How does the Auto-Patch node work?
The Auto-Patch cuts the artwork on the Colour Art layer with the artwork on the Line Art layer, creating a cutter shape that is exactly on the edge of the adjacent artwork. These two shapes meeting precisely creates the anti-aliasing line in the Render view as the blurred pixels show the background colour through.
| Auto-Patch Cutter in OpenGL | Auto-Patch Cutter in Render view |
How do I fix it?
You can fix the anti-aliasing issue by removing the Auto-Patch and using a Colour-Art and Line-Art node instead. For more information, see How do I mask one part inside another? Keep in mind that this technique will not work if your fill is up to the edge of the line, or you have no line art. Continue reading for more.
Invert cutting with a brush line fill
If you draw a brush line and fill it directly on the Line Art layer, it will create a fill that reaches the edge of the brush shape. If you then paste this fill onto the Colour Art layer and create an invert-cutter system, you will get the anti-aliasing line in the Render view, even if you use the correct invert-cutting technique.
How do I fix it?
It is always recommended that you use Pencil lines for any artwork used in rigs and cutting systems as they always fill to the centre of the line. However, if you must use brush lines, do not fill the shape on the Line Art layer and then cut and paste it on the Colour Art layer. Instead, use the Create Colour Art from Line Art button as this will create a stroke on the Colour Art layer that reaches the centre of the line. Then fill the shape on the Colour Art layer.
Invert cutting without line art
Sometimes you have a character design that has little to no line art. This means any artwork that is invert-cut will automatically create the anti-aliasing line because the edges of the artwork will be right up against each other with no line art to hide it.
How do I fix it?
The line can be hidden by the existing artwork by adding an Increase Opacity node into the cutter system. The Increase Opacity node will allow you to expand the artwork just enough to hide the issue. See Increase Opacity Node for more information.
| Before Increase Opacity node | After Increase Opacity node |