Processing.py 空白窗口问题

Question

I tried writing an A* alg using processing.py but I am having an issue with the beginning of the code: my window is totally blank

So, I want a grid to appear waiting for the user to click on a cell and then to fill that cell with a black rectangle. But, I only want this to run at the beginning of my code so I didn't put it in the draw function.

Here is my code:

taille = 400
pas = taille // 20

def setup():
    size(taille, taille)
    background(255, 255, 255)
    stroke(0)
    strokeWeight(2)
    frameRate(20)
    for i in range(pas, taille, pas):
        line(i, 0, i, taille)
        line(0, i, taille, i)
    drawRect()

def drawRect():    
    x, y = pressed()
    for i in range(1, taille // pas - 1):
        for j in range(1, taille // pas - 1):
            if i * pas <= x and x <= (i + 1) * pas:
                if j * pas <= y and y <= (j + 1) * pas:
                    rect(i * pas, j * pas, pas, pas)

def pressed():
    while True:
        if mousePressed:
            return (mouseX, mouseY)        

I highly suspect that the error is coming from the drawRect function since I managed to display the grid before adding it.

Answer 1

So, I want a grid to appear waiting for the user to click on a cell and then to fill that cell with a black rectangle. But, I only want this to run at the beginning of my code so I didn't put it in the draw function.

Anyway I recommend to use a draw function, to continuously draw the scene dependent on the current states of your program.

Note, your program hangs in an endless loop. The variables mousePressed , mouseX and mouseY are never updated. This variables don't change their state magically. They change their state between 2 frames, after the draw function has been executed Processing does the event handling and changes the built in variables. You don't give Processing any chance to do this job.

Create to variables, which notice the x and y window coordinate of the "click":

enter_x = -1
enter_y = -1

Implement the mousePressed event to receive the "click":

def mousePressed():
global enter_x, enter_y
if enter_x < 0 or enter_y < 0:
    enter_x = mouseX
    enter_y = mouseY 

Draw the black rectangle to the if the "click" coordinates are valid ( >= 0 ) in the draw function :

def draw():   
    global enter_x, enter_y

    if enter_x >= 0 and enter_y >= 0:
        stroke(0)  
        fill(0)
        ix = enter_x // pas
        iy = enter_y // pas
        rect(ix * pas, iy * pas, pas, pas)

The full code may look like this:

taille = 400
pas = taille // 20

def setup():
    size(taille, taille)
    background(255, 255, 255)
    stroke(0)
    strokeWeight(2)
    frameRate(20)
    for i in range(pas, taille, pas):
        line(i, 0, i, taille) 
        line(0, i, taille, i)

enter_x = -1
enter_y = -1

def mousePressed():
    global enter_x, enter_y
    if enter_x < 0 or enter_y < 0:
        enter_x = mouseX
        enter_y = mouseY    

def draw():   
    global enter_x, enter_y

    if enter_x >= 0 and enter_y >= 0:
        stroke(0)  
        fill(0)
        ix = enter_x // pas
        iy = enter_y // pas
        rect(ix * pas, iy * pas, pas, pas)

Note, it may be necessary to draw the grid in the draw function too. In general it is better to redraw the scene every frame, than "undoing" something what has been draw.