Pygame - blitting预览图片

Question

First off, this is a school assignment so I want to be upfront about that. Second I'm just asking for advice on the approach, possible help with the code. I'm working on a MSPAINT style clone using some pre-existing code from our book. The code already has the use of the draw.line when pressing mouse button 1. Teacher wants us to add ability to make circles or rectangles. I'm working on the circle part and I have figured out (thanks to the forums on here) how to implement what I wanted to do with the MOUSEBUTTONDOWN and MOUSEBUTTONUP events.. This has brought me to a new Question.. How would I blit then erase then blit a preview of the circle until it is the size the user wants and they release the MOUSEBUTTON and view the final blit...

while keepGoing:
    clock.tick(30)

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            keepGoing = False
        elif event.type == pygame.MOUSEMOTION:
            lineEnd = pygame.mouse.get_pos()
            if pygame.mouse.get_pressed() == (1,0,0):
                pygame.draw.line(background, drawColor, lineStart, lineEnd, lineWidth)
            lineStart = lineEnd
        elif event.type == pygame.MOUSEBUTTONDOWN and event.button == 3:
                    circleStart = pygame.mouse.get_pos()
        elif event.type == pygame.MOUSEBUTTONUP and event.button == 3: 
                    circleEnd = pygame.mouse.get_pos()
                    size = (circleEnd[0] - circleStart[0])
                    pygame.draw.circle(background, drawColor, circleStart, size, lineWidth)
        elif event.type == pygame.KEYDOWN:
            myData = (event, background, drawColor, lineWidth, keepGoing)
            myData = checkKeys(myData)
            event, background, drawColor, lineWidth, keepGoing) = myData

Thanks so much

-Ben

Answer 1

So after some thinking this is the best solution I came up with using pygame. Tell me what you think and if it has helped you.

import pygame,sys,math #---- Import modules we will need

pygame.init() #---- Initialize the module

def get_rad(origin_x,origin_y,x,y): #----- Returns the appropriate radius
    return math.sqrt((origin_x - x)**2 + (origin_y - y)**2) #----- Distance between 2
                                                            #----- points

screen = pygame.display.set_mode((400,400)) #----- Sets up the screen
clock  = pygame.time.Clock() #------- Sets up the clock

mouse_button = 0 #--------- This variable is used to determine whether a mouse button
                 #--------- has been pressed

draw_final_circle = False #---------- This variable lets us know that we should draw the 
                          #---------- final circle

while True: #------ main loop

    clock.tick(60) #------ Limit the Fps

    mouse_button0  = mouse_button #-------- This variable holds the previous value of 
                                  #-------- mouse_button(it will be useful later)

    mouse_x,mouse_y = pygame.mouse.get_pos() #----- Get the mosue coordinates

    for e in pygame.event.get(): #---- Cycle through events

        if e.type == pygame.QUIT: pygame.quit();sys.exit() #--Quit when window is closed

        if e.type == pygame.MOUSEBUTTONDOWN: #---- If the mouse button is pressed
            if mouse_button == 0: #---- if the mouse button is released
                mouse_button = 1 #----- set it to pressed basically
                originx,originy = mouse_x,mouse_y #---- keep the mouse_x,mouse_y pos

        if e.type == pygame.MOUSEBUTTONUP: #---- if the mouse button is released
             if mouse_button == 1: #-------- if it is pressed
                 mouse_button = 0 #--------- set it to released

    screen.fill((255,255,255)) #---- clear the screen


    #-------- If a mouse button is pressed and a circle can be drawn (rad>width) ------#
    if mouse_button == 1 and get_rad(originx,originy,mouse_x,mouse_y) > 1:

        rad = int(get_rad(originx,originy,mouse_x,mouse_y)) #---- get the radius(as int)
        pos = mouse_x,mouse_y
        pygame.draw.circle(screen,(0,0,0),pos,rad,1) #--- draw the circle

    #----------------------------------------------------------------------------------#


    #---------- if the button is released but in the previous loop it was pressed -----#
    if mouse_button == 0 and mouse_button0 == 1:

        draw_final_circle = True #----- set the final circle boolean to True

    if draw_final_circle: #----- if the final circle is decided
        pygame.draw.circle(screen,(0,0,0),pos,rad,1) #---- keep drawing it 

    pygame.display.flip() #----- flip the buffer

Answer 2

I suggest you implement the different modes of your drawing program into different classes that represent the current mode and its state. This way, implementing different modes become very easy.

---

As for a circle drawing mode, you want to take a copy the screen surface when the user presses the mouse button, and blit that copy to the screen every frame.

Then draw your circle on that copy. This way, you basically "erase" the temporary circles.

---

Here's a simple example. Press SPACE to cycle between the different modes (draw, circle, rect) and TAB for different colors:

import pygame
from math import hypot
from itertools import cycle
from operator import itemgetter

pygame.init()
screen = pygame.display.set_mode((400, 400))
clock = pygame.time.Clock()

colors = cycle(sorted(pygame.color.THECOLORS.iteritems(), key=itemgetter(0)))
color = next(colors)[1]

class DrawMode(object):
    def __init__(self):
        self.last = None
    def handle(self, e):
        if e.type == pygame.MOUSEBUTTONDOWN and e.button == 1:
            self.last = pygame.mouse.get_pos()
        if e.type == pygame.MOUSEBUTTONUP and e.button == 1:
            self.last = None
    def draw(self, screen):
        pos = pygame.mouse.get_pos()
        if self.last:
            pygame.draw.line(screen, color, self.last, pos)
            self.last = pos

class ClickReleaseMode(object):
    def __init__(self):
        self.tmp = None
        self.start = None
    def handle(self, e):
        if e.type == pygame.MOUSEBUTTONDOWN and e.button == 1:
            self.start = pygame.mouse.get_pos()
        if e.type == pygame.MOUSEBUTTONUP and e.button == 1:
            self.start = self.tmp = None
    def draw(self, screen):
        if not self.tmp:
            self.tmp = screen.copy()

        pos = pygame.mouse.get_pos()
        screen.blit(self.tmp, (0,0))
        if self.start:
            self.do_draw(screen, pos)

class CircleMode(ClickReleaseMode):
    def __init__(self):
        super(CircleMode, self).__init__()

    def do_draw(self, screen, pos):
        r = hypot(pos[0] - self.start[0], pos[1] - self.start[1])
        if r >= 2:
            pygame.draw.circle(screen, color, self.start, int(r), 2)

class RectMode(ClickReleaseMode):#
    def __init__(self):
        super(RectMode, self).__init__()

    def do_draw(self, screen, pos):
        p = pos[0] - self.start[0], pos[1] - self.start[1]
        pygame.draw.rect(screen, color, pygame.Rect(self.start, p), 2)

quit = False
modes = cycle((DrawMode, CircleMode, RectMode))
mode = next(modes)()
while not quit:
    quit = pygame.event.get(pygame.QUIT)
    for e in pygame.event.get():
        if e.type == pygame.KEYDOWN:
            if e.key == pygame.K_SPACE:
                mode = next(modes)()
                print 'enter', mode.__class__.__name__
            if e.key == pygame.K_TAB:
                name, color = next(colors)
                print 'changing color to', name, color
        mode.handle(e)
    mode.draw(screen)
    pygame.display.flip()
    clock.tick(60)