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Old 24 September 2016, 20:04   #1
mark_k
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Join Date: Aug 2004
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Posts: 2,481
Bilinear filter wraparound?

I noticed a small issue with scaling & bilinear filtering. This could be due to WinUAE considering the texture (Amiga image) to be tiled when doing bilinear filtering.

The effect of that seems to be, if the top row of pixels is a different colour to the bottom row, the bottom row after bilinear filtering has a "shadow" of the top row. The same probably applies to the left and right edges.

The solution may be to consider the texture as mirrored at the edges, or (effectively) repeat the edge rows/columns.

In practice this is a very minor problem which perhaps no-one ever noticed before, since typically the top and bottom rows of an Amiga display (and the left and right) are all the same colour.

Example pics attached. HighGfx 1024768, scaling 1.5. One with point filtering, the other bilinear. The bilinear pic has a helpful red arrow pointing to the problem line. If I drag the screen down by a pixel that line disappears. Strangely though, the "problem line" doesn't have the dark blue border colour on its left and right edges.
Attached Thumbnails
Click image for larger version

Name:	Point_1.5x.png
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Size:	10.4 KB
ID:	50096   Click image for larger version

Name:	Bilinear_1.5x.png
Views:	83
Size:	165.7 KB
ID:	50097  
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