Processing: Creative Coding and Computational Art

PROCESSING: CREATIVE CODING AND COMPUTATIONAL ART
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Figure 9-2. rectMode() example
The default mode is rectMode(CORNER), which draws the rectangle from the top-left
corner. Since this is the default, I didn’t need to explicitly call it in the sketch. The CENTER
and CORNER modes treat the four rect() arguments as x, y, width, and height. However,
the CORNERS mode treats the four arguments as x1, y1, x2, y2, specifying the top-left and
bottom-right corner points of the rectangle. If I add one more rect() call to the bottom
of the program, without specifying another drawing mode call, what mode do you think
will be used? This question is a little tricky, as many people will assume the default state
(CORNER) will be used, but the answer is actually (CORNERS). Every time you issue one of
these drawing mode commands in a program, you change the current state of the drawing
mode. This type of programming change is referred to as a state change, as you are changing
the drawing state of the program, at least in terms of drawing rectangles.
Processing’s ellipse() function, which has the same four parameters as rect(int x,
int y, int w, int h), works similarly. However, as mentioned earlier, the default drawing
mode for ellipse() is ellipseMode(CENTER). ellipse() also has access to one
additional mode, ellipseMode(CENTER_RADIUS). This mode does the same thing as
CENTER, only it treats the width and height arguments as radii rather than diameters. One
somewhat useful thing to do with these two modes together is to quickly generate an
ellipse within an ellipse (see Figure 9-3):
size(400, 400);
background(255);
strokeWeight(10);
fill(127);
ellipseMode(CENTER_RADIUS);
ellipse(200, 200, 170, 170);
fill(255);
ellipseMode(CENTER);
ellipse(200, 200, 170, 170);