Processing学习笔记 之 Processing简要执行过程

参考文献：http://processing.org/reference/

 

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Processing执行过程：

第一步执行setup()

Called once when the program is started. Used to define initial enviroment properties such as screen size, background color, loading images, etc. before the draw() begins executing. Variables declared within setup() are not accessible within other functions, includingdraw(). There can only be one setup() function for each program and it should not be called again after it's initial execution.

 

第二步执行draw()

Called directly after setup() and continuously executes the lines of code contained inside its block until the program is stopped or noLoop() is called. The draw()function is called automatically and should never be called explicitly. It should always be controlled with noLoop(), redraw() and loop(). After noLoop() stops the code indraw() from executing, redraw() causes the code inside draw() to execute once and loop() will causes the code inside draw() to execute continuously again. The number of times draw() executes in each second may be controlled with the delay()and frameRate() functions. There can only be one draw() function for each sketch and draw() must exist if you want the code to run continuously or to process events such as mousePressed(). Sometimes, you might have an empty call to draw() in your program as shown in the above example.

 

loop()

Causes Processing to continuously execute the code within draw(). If noLoop() is called, the code in draw() stops executing.

 

noLoop()

Stops Processing from continuously executing the code within draw(). If loop() is called, the code in draw() begin to run continuously again. If using noLoop() insetup(), it should be the last line inside the block. 
When noLoop() is used, it's not possible to manipulate or access the screen inside event handling functions such as mousePressed() or keyPressed(). Instead, use those functions to call redraw() or loop(), which will run draw(), which can update the screen properly. This means that when noLoop() has been called, no drawing can happen, and functions like saveFrame() or loadPixels() may not be used. 
Note that if the sketch is resized, redraw() will be called to update the sketch, even after noLoop() has been specified. Otherwise, the sketch would enter an odd state until loop() was called.