The PLplot Plotting Library: Programmer's Reference Manual
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### `plshade1`: Shade individual region on the basis of value

`plshade1` (a, nx, ny, defined, xmin, xmax, ymin, ymax, shade_min, shade_max, sh_cmap, sh_color, sh_width, min_color, min_width, max_color, max_width, fill, rectangular, pltr, pltr_data);

Shade individual region on the basis of value. Use `plshades` if you want to shade a number of contiguous regions using continuous colors. In particular the edge contours are treated properly in `plshades`. If you attempt to do contiguous regions with `plshade1` (or `plshade`) the contours at the edge of the shade are partially obliterated by subsequent plots of contiguous shaded regions. `plshade1` differs from `plshade` by the type of the first argument. Look at the argument list below, `plcont` and the Section called Contour and Shade Plots in Chapter 3 for more information about the transformation from grid to world coordinates. Shading NEEDS DOCUMENTATION, but as a stopgap look at how `plshade` is used in `examples/c/x15c.c`

`a` (`PLFLT *`, input) Contains array to be plotted. The array must have been declared as PLFLT a[nx][ny]. `nx` (`PLINT`, input) First dimension of array "a". `ny` (`PLINT`, input) Second dimension of array "a". `defined` (`PLINT (*) (PLFLT, PLFLT)`, input) User function specifying regions excluded from the shading plot. This function accepts x and y coordinates as input arguments and must return 0 if the point is in the excluded region or 1 otherwise. This argument can be NULL if all the values are valid. `xmin` (`PLFLT`, input) Defines the "grid" coordinates. The data a[0][0] has a position of (xmin,ymin), a[nx-1][0] has a position at (xmax,ymin) and so on. `xmax` (`PLFLT`, input) Defines the "grid" coordinates. The data a[0][0] has a position of (xmin,ymin), a[nx-1][0] has a position at (xmax,ymin) and so on. `ymin` (`PLFLT`, input) Defines the "grid" coordinates. The data a[0][0] has a position of (xmin,ymin), a[nx-1][0] has a position at (xmax,ymin) and so on. `ymax` (`PLFLT`, input) Defines the "grid" coordinates. The data a[0][0] has a position of (xmin,ymin), a[nx-1][0] has a position at (xmax,ymin) and so on. `shade_min` (`PLFLT`, input) Defines the lower end of the interval to be shaded. If shade_max ≤ shade_min, `plshade1` does nothing. `shade_max` (`PLFLT`, input) Defines the upper end of the interval to be shaded. If shade_max ≤ shade_min, `plshade1` does nothing. `sh_cmap` (`PLINT`, input) Defines color map. `sh_color` (`PLFLT`, input) Defines color map index if cmap0 or color map input value (ranging from 0. to 1.) if cmap1. `sh_width` (`PLINT`, input) Defines width used by the fill pattern. `min_color` (`PLINT`, input) Defines pen color, width used by the boundary of shaded region. The min values are used for the shade_min boundary, and the max values are used on the shade_max boundary. Set color and width to zero for no plotted boundaries. `min_width` (`PLINT`, input) Defines pen color, width used by the boundary of shaded region. The min values are used for the shade_min boundary, and the max values are used on the shade_max boundary. Set color and width to zero for no plotted boundaries. `max_color` (`PLINT`, input) Defines pen color, width used by the boundary of shaded region. The min values are used for the shade_min boundary, and the max values are used on the shade_max boundary. Set color and width to zero for no plotted boundaries. `max_width` (`PLINT`, input) Defines pen color, width used by the boundary of shaded region. The min values are used for the shade_min boundary, and the max values are used on the shade_max boundary. Set color and width to zero for no plotted boundaries. `fill` (`void (*) (PLINT, PLFLT *, PLFLT *)`, input) Routine used to fill the region. Use `plfill`. Future version of plplot may have other fill routines. `rectangular` (`PLBOOL`, input) Set ``rectangular`` to true if rectangles map to rectangles after coordinate transformation with ``pltrl``. Otherwise, set ``rectangular`` to false. If ``rectangular`` is set to true, plshade tries to save time by filling large rectangles. This optimization fails if the coordinate transformation distorts the shape of rectangles. For example a plot in polor coordinates has to have ``rectangular`` set to false. `pltr` (`void (*) (PLFLT, PLFLT, PLFLT *, PLFLT *, PLPointer)` , input) Pointer to function that defines transformation between indices in array ``z`` and the world coordinates (C only). Transformation functions are provided in the PLplot library: `pltr0` for identity mapping, and `pltr1` and `pltr2` for arbitrary mappings respectively defined by one- and two-dimensional arrays. In addition, user-supplied routines for the transformation can be used as well. Examples of all of these approaches are given in the Section called Contour Plots from C in Chapter 3. The transformation function should have the form given by any of `pltr0`, `pltr1`, or `pltr2`. `pltr_data` (`PLPointer`, input) Extra parameter to help pass information to `pltr0`, `pltr1`, `pltr2`, or whatever routine that is externally supplied.

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