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bitmaptools: dither: get rid of shifts 

this happens to make the occasional FS dither artifact disappear.
I guess `a * b >> 8` and `(a * b) / 256` are not identical.  I'm not
sure if it was just the parens or not, but write the clearer code and
rely on the compiler to substitute an appropriate shift if possible.
This commit is contained in:
Jeff Epler 2021-11-24 09:48:32 -06:00
parent 9af76a2f03
commit 30c07a772f
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GPG Key ID: D5BF15AB975AB4DE
1 changed files with 4 additions and 4 deletions
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8
shared-module/bitmaptools/__init__.c
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@ -749,9 +749,9 @@ void common_hal_bitmaptools_dither(displayio_bitmap_t *dest_bitmap, displayio_bi
int x1 = x + info->terms[i].dx;
int dy = info->terms[i].dy;
rows[dy][x1] = ((info->terms[i].dl * err) >> 8) + rows[dy][x1];
rows[dy][x1] = ((info->terms[i].dl * err) / 256) + rows[dy][x1];
}
err = err * info->dl >> 8;
err = (err * info->dl) / 256;
}
write_pixels(dest_bitmap, y, out);
@ -779,9 +779,9 @@ void common_hal_bitmaptools_dither(displayio_bitmap_t *dest_bitmap, displayio_bi
int x1 = x - info->terms[i].dx;
int dy = info->terms[i].dy;
rows[dy][x1] = ((info->terms[i].dl * err) >> 8) + rows[dy][x1];
rows[dy][x1] = ((info->terms[i].dl * err) / 256) + rows[dy][x1];
}
err = err * info->dl >> 8;
err = (err * info->dl) / 256;
}
write_pixels(dest_bitmap, y, out);