AtlasEngine: Curly line redux (#17508)

See #17501.

(cherry picked from commit 7f2249c)
Service-Card-Id: 92942980
Service-Version: 1.21

src/renderer/atlas/BackendD2D.cpp

@@ -658,24 +658,14 @@ void BackendD2D::_drawGridlineRow(const RenderingPayload& p, const ShapedRow* ro
         // it being simple to implement and robust against more peculiar fonts with unusually large/small descenders, etc.
         // We still need to ensure though that it doesn't clip out of the cellHeight at the bottom, which is why `position` has a min().
         const auto height = std::max(3.0f, duBottom + duHeight - duTop);
-        const auto position = std::min(duTop, cellHeight - height - duHeight);
+        const auto position = std::min(duTop, cellHeight - height);
 
         // The amplitude of the wave needs to account for the stroke width, so that the final height including
         // antialiasing isn't larger than our target `height`. That's why we calculate `(height - duHeight)`.
-        //
-        // In other words, Direct2D draws strokes centered on the path. This also means that (for instance)
-        // for a line width of 1px, we need to ensure that the amplitude passes through the center of a pixel.
-        // Because once the path gets stroked, it'll occupy half a pixel on either side of the path.
-        // This results in a "crisp" look. That's why we do `round(amp + half) - half`.
-        const auto halfLineWidth = 0.5f * duHeight;
-        const auto amplitude = roundf((height - duHeight) * 0.5f + halfLineWidth) - halfLineWidth;
-        // While the amplitude needs to account for the stroke width, the vertical center of the wave needs
-        // to be at an integer pixel position of course. Otherwise, the wave won't be vertically symmetric.
-        const auto center = cellCenter + position + amplitude + halfLineWidth;
-
-        const auto top = center - 2.0f * amplitude;
-        const auto bottom = center + 2.0f * amplitude;
-        const auto step = 0.5f * height;
+        const auto center = cellCenter + position + 0.5f * height;
+        const auto top = center - (height - duHeight);
+        const auto bottom = center + (height - duHeight);
+        const auto step = roundf(0.5f * height);
         const auto period = 4.0f * step;
 
         const auto from = r.from * scaledCellWidth;