John Aldridge - 2018-01-20

Hi,

I hope I'm not treading on toes here...

I found what I believe to be a bug (or at least a misfeature) in PHPlot, which I developed a fix for. I would like to (a) discuss whether this is indeed the appropriate fix, and if so (b) contribute it back to the community. The web site phplot.org refers to a repository on github, but there seems to be no activity and the code there seems to be identical to that here. The only active forum I've found is this one, so here goes...

There are comments in the PHPlot code for DrawYAxis()

  • This draws the Y axis and grid lines. It must be called before DrawXAxis() to avoid
  • having a horizontal grid line overwrite the X axis.

which mostly prevents the described problem except in cases like

<?php

include_once('phplot.php');

$plot = new PHPlot(300, 300);
$plot->SetPlotAreaWorld(-10, -5, 5, 10);

$plot->SetDataType('data-data');

$plot->SetDataValues(array(
    array('', -5, 0),
    array('', 0, 5),
    array('', 5, 0),
    array('', 0, -5),
    array('', -5, 0)
));

$plot->SetDrawXAxis(TRUE);
$plot->SetDrawYAxis(TRUE);

$plot->SetXAxisPosition(0);
$plot->SetYAxisPosition(0);

$plot->SetDrawXGrid(TRUE);
$plot->SetDrawYGrid(TRUE);

$plot->DrawGraph();

?>

where both X and Y axes are drawn. In this case, a vertical grid line overwrites the Y axis. The fix I came up with was to change DrawXTicks() and DrawYTicks() to only draw the grid line if there wasn't an axis at the same position, vis...

***************
*** 6141,6147 ****
              $x_pixels = $this->xtr($x);

              // Draw vertical grid line:
!             if ($draw_grid) {
                  ImageLine($this->img, $x_pixels, $this->plot_area[1], $x_pixels, $this->plot_area[3], $style);
              }

--- 6138,6144 ----
              $x_pixels = $this->xtr($x);

              // Draw vertical grid line:
!             if ($draw_grid && ($x_pixels != $this->y_axis_x_pixels || $this->suppress_y_axis)) {
                  ImageLine($this->img, $x_pixels, $this->plot_area[1], $x_pixels, $this->plot_area[3], $style);
              }

***************
*** 6172,6178 ****
              $y_pixels = $this->ytr($y);

              // Draw horizontal grid line:
!             if ($draw_grid) {
                  ImageLine($this->img, $this->plot_area[0]+1, $y_pixels, $this->plot_area[2]-1,
                            $y_pixels, $style);
              }
--- 6169,6175 ----
              $y_pixels = $this->ytr($y);

              // Draw horizontal grid line:
!             if ($draw_grid && ($y_pixels != $this->x_axis_y_pixels || $this->suppress_x_axis)) {
                  ImageLine($this->img, $this->plot_area[0]+1, $y_pixels, $this->plot_area[2]-1,
                            $y_pixels, $style);
              }

Which solves the problem for me.

So... (a) is this a good fix, and if so (b) how do I go about getting it adopted by the maintainers?

Cheers,
John