[rrd-developers] Re: placement of y-axis gridlines

Peter Speck speck at ruc.dk
Mon Apr 15 23:24:41 MEST 2002

Hi Tobi et.al.,

Here's the patch for evenly-spaced y-axis gridlines.

I had to split horizontal_grid() into calc_horizontal_grid and 
draw_horizontal_grid as the calculated info is needed in the adjustment 
code. My previous patch had the problem that it adjusted the y-axis too 
late, e.g. after the data lines was drawn.
The result of the calc is stored in struct ygrid_scale_t which 
image_desc_t has as a member.

--no-gridfit is implemented.

The round-to-integer coordinates for png is moved to the libart code in 
rrd_gfx. The 'close path' code is cleaned up so the node list is left 
unchanged if you want to save the same graph in multiple formats in one 
run. The rounding is done on the scaled coordinates (zoom).

I have made a simple version for logarithmic y scales as such a scale 
might have 5 gridlines with 4 difference spacings. This version only 
uses y = 10^x values for modifying the scale.

My old patch often reduced the scale. That bug is fixed, and I have 
added alignment of first gridline if im->minval happended to place that 
on non-integer y pixel pos.


  - Peter Speck

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