+
+The original code draws every grid point on screen, even the ones that are
+off the board. When the user zooms out with a dense grid, it can become too
+dense - the original code turns the grid off in this case.
+
+If the grid is very dense, on a large screen the software render may slow down.
+This is noticeable in pan and zoom mostly. The bottleneck is the gtk call
+that draws the grid points: if there are too many of them, it's slow.
+
+
+
New grid
+
+To overcome this problem, pcb-rnd offers configuration settings to limit
+the number of dots to be drawn. There are mainly two parallel approaches:
+using a local grid or draw less dots in a global grid. The
+old code defined only a global grid and did not have runtime settings for
+the properties of the grid.
+
+
Global grid improvements
+
+The most trivial optimization is that grid points off the board are simply
+not drawn:
+
+
+
+Next, the compile-time configurable "minimum distance between grid points
+before it is too dense" setting is user configurable now. The default value
+can be changed in any of the usual
+configuration sources. However,
+when the configured density is reached while zooming out, there are two options.
+
+The first, default option is to do the same that the original code did: just
+hide the grid:
+
+
+
+An alternative is to use sparse global grid which means only
+every 2nd, 3rd, 4th, ... Nth grid point is drawn. The cursor still snaps
+to every real grid point, so the grid got sparse only on the display. Note
+how the line is drawn on invisible grid points:
+
+
+
+
Introduction of the local grid
+Another approach is to use a local grid. The grid helps finding whether
+existing objects are aligned or where the next move/click would end up.
+These are usually interesting only in a small range around the crosshair and
+less interesting on the other end of the board. Local grid draws the grid
+points only near the crosshair. Such local grid follows the crosshair
+everywhere:
+
+
+
+The user can configure or interactively set the radius in which the grid
+points are drawn:
+
+
+
+The radius is given in "number of grid points", thus the local grid yields
+a constant number of points that is independent of the actual grid size. When
+a local grid gets too dense, it is hidden - there's no sparse option, since
+local grids usually have too few points to make reasonable skips.
+
+
save/load and compatibility
+Not affected.
+
+
plans
+This feature is gtk-specific and is complete. There are no plans to
+implement this in the lesstif HID at the moment.
+
+
+
Index: trunk/doc-rnd/features/grid_edge.png
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Index: trunk/doc-rnd/features/grid_global_sparse.png
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Index: trunk/doc-rnd/features/grid_local_16.png
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@@ -46,7 +46,8 @@
+
+
+
+
+
+
+