Thursday, 26 March 2009

Drawing some grids

All done! Make a separate copy of Listing CC.2 by starting a new sketch and pasting the code into the window. Replace the dummy drawGrid() stub with the one in Listing CC.3, type in the drawVertGrid() and drawHorzGrid() functions, save the file with a name of your choice and run the program.
Try changing the number of cells in either or both directions by altering the variables shown in Listing CC.2, make the grid larger or smaller in either or both directions, change its left, top origin and so on. If you only want grid lines running in one direction pass zero for cells in that direction. Optionally, put additional calls in the Listing CC.2 code to draw several grids in different locations, perhaps with different colours and opacities using loops to change line style for calls to drawGrid(). Figure CC.3 shows an example.

Figure CC.3 Effects produced by drawing multiple and overlapping grids.

Drawing unequal cell sizes

Grid line spacing can follow any rule: logarithmic, quadratic, cubic, Fibonacci, etc. or can be random. Another version of drawVertGrid() draws grid lines with logarithmic spacing:

void drawVertGrid(int left, int top, int right, int bottom, int width,
int xCells){

if ( xCells <= 0 ) return;

int m = xCells + 1;
float logCells = log(m);
for (int i = 2; i <= m; i++) {
int x = left + round(log(i)/logCells * width);
line(x, top, x, bottom);

In this case the loop variable is an integer and values from 2 to m are submitted to the computation to get offsets from the grid's left coordinate. Working out line intervals relies on logm(x) = log(x) / log (m). Log(1) is zero, the grid's left origin, so m is (numCells + 1). Alternatively you may wish to ignore these facts and just look at the nice dynamic that logarithmic spacing gets for any number of lines drawn across the face of a grid.

Figure CC.4
Logarithmic and Circular Grid parametrics.

Using a rule more complex than logarithmic the easiest way to make cell sizes follow the drawGrid() specification for a specified number of cells with an exact fit to the grid is to compute relative sizes and store them them in an array. If predetermined relative sizes are needed to give an effect these values can be assigned when the array is created. The drawing loop simply uses the ratio between the sum of the sizes in the array and the dimension of the grid to work out line positions. Doing this needs slightly more code that the grid-line drawing functions we have investigated at so far and we can return to this variation later.

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