drawing grids fast

["Vassilios V . Dimakopoulos" <dimako cs uoi gr>]

Hello all,

here is my "simple" question: I write a vector drawing application
which has a drawing area and a backing pixmap. The user may select
to show/hide grid lines or points.

What would be the best way to draw the grid?

I have tried two basic methods:
(1) drawing expicitely horizontal/vertical lines on the pixmap and then
    copying it onto the drawing area: relatively slow since the grid can
    be quite dense; gdk_draw_segments() is useful, but the speed difference
    is not that high. (also, what if the user wants a point grid ?)

(2) filling the pixmap with small horizontal & vertical pixmaps, which if
    manipulated correctly (XOR operations, etc) produce the final line/point 
grid.
    This is faster than (1) when the window is relatively small.
    For bigger windows, it gets too slow.

The slowdown shows up when scrolling, where everything gets repainted.
I have noticed, however, that e.g. Kontour has no speed penalties when the
grid is turned on.

Does anyboby have a suggestion?


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VASSILIOS V. DIMAKOPOULOS             Office: +30-6510-98809
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