As I see it, there are two ways to handle mouse events to draw a picture.
The first is to detect when the mouse moves and draw a line to where the mouse is, shown here. However, the problem with this is that with a large brush size, many gaps appear between each "line" that is not straight since it is using the line's stroke size to create thick lines.
The other way is to draw circles when the mouse moves as is shown here. The problem with this is that gaps appear between each circle if the mouse moves faster than the computer detects mouse input.
Here's a screenshot with my issues with both:
What is the best way to implement a brush like MS Paint's, with a decently-big brush size with no gaps in the stroke of the line or no gaps between each circle?
Why not do both?
Draw a circle at each endpoint and a line between the two.
EDIT rofl, just couldn't stop myself.
Actually, you don't want to use pygame.draw.line because it cheats. It fills a 1 pixel wide row or column (depending on angle of attack) of pixels. If you do go at a roughly perpendicular angle, 0 deg or 90 deg, this isn't an issue, but at 45's, you'll notice a sort of string bean effect.
The only solution is to draw a circle at every pixel's distance. Here...
import pygame, random
screen = pygame.display.set_mode((800,600))
draw_on = False
last_pos = (0, 0)
color = (255, 128, 0)
radius = 10
def roundline(srf, color, start, end, radius=1):
dx = end[0]-start[0]
dy = end[1]-start[1]
distance = max(abs(dx), abs(dy))
for i in range(distance):
x = int( start[0]+float(i)/distance*dx)
y = int( start[1]+float(i)/distance*dy)
pygame.draw.circle(srf, color, (x, y), radius)
try:
while True:
e = pygame.event.wait()
if e.type == pygame.QUIT:
raise StopIteration
if e.type == pygame.MOUSEBUTTONDOWN:
color = (random.randrange(256), random.randrange(256), random.randrange(256))
pygame.draw.circle(screen, color, e.pos, radius)
draw_on = True
if e.type == pygame.MOUSEBUTTONUP:
draw_on = False
if e.type == pygame.MOUSEMOTION:
if draw_on:
pygame.draw.circle(screen, color, e.pos, radius)
roundline(screen, color, e.pos, last_pos, radius)
last_pos = e.pos
pygame.display.flip()
except StopIteration:
pass
pygame.quit()
Not blitting at each loop step can improve the speed of the drawing (using this code adapted from the previous one allow to remove lag problem on my machine)
import pygame, random
screen = pygame.display.set_mode((800,600))
draw_on = False
last_pos = (0, 0)
color = (255, 128, 0)
radius = 10
def roundline(srf, color, start, end, radius=1):
dx = end[0]-start[0]
dy = end[1]-start[1]
distance = max(abs(dx), abs(dy))
for i in range(distance):
x = int( start[0]+float(i)/distance*dx)
y = int( start[1]+float(i)/distance*dy)
pygame.display.update(pygame.draw.circle(srf, color, (x, y), radius))
try:
while True:
e = pygame.event.wait()
if e.type == pygame.QUIT:
raise StopIteration
if e.type == pygame.MOUSEBUTTONDOWN:
color = (random.randrange(256), random.randrange(256), random.randrange(256))
pygame.draw.circle(screen, color, e.pos, radius)
draw_on = True
if e.type == pygame.MOUSEBUTTONUP:
draw_on = False
if e.type == pygame.MOUSEMOTION:
if draw_on:
pygame.display.update(pygame.draw.circle(screen, color, e.pos, radius))
roundline(screen, color, e.pos, last_pos, radius)
last_pos = e.pos
#pygame.display.flip()
except StopIteration:
pass
pygame.quit()
For the first problem, you need have a background, even if its just a color. I had the same problem with a replica pong game i made. Here is an example of a replica paint program I made, left click to draw, right click to erase, click on the color image to choose a color, and up button to clear screen:
import os
os.environ['SDL_VIDEO_CENTERED'] = '1'
from pygamehelper import *
from pygame import *
from pygame.locals import *
from vec2d import *
from math import e, pi, cos, sin, sqrt
from random import uniform
class Starter(PygameHelper):
def __init__(self):
self.w, self.h = 800, 600
PygameHelper.__init__(self, size=(self.w, self.h), fill=((255,255,255)))
self.img= pygame.image.load("colors.png")
self.screen.blit(self.img, (0,0))
self.drawcolor= (0,0,0)
self.x= 0
def update(self):
pass
def keyUp(self, key):
if key==K_UP:
self.screen.fill((255,255,255))
self.screen.blit(self.img, (0,0))
def mouseUp(self, button, pos):
pass
def mouseMotion(self, buttons, pos, rel):
if pos[1]>=172:
if buttons[0]==1:
#pygame.draw.circle(self.screen, (0,0,0), pos, 5)
pygame.draw.line(self.screen, self.drawcolor, pos, (pos[0]-rel[0], pos[1]-rel[1]),5)
if buttons[2]==1:
pygame.draw.circle(self.screen, (255,255,255), pos, 30)
if buttons[1]==1:
#RAINBOW MODE
color= self.screen.get_at((self.x, 0))
pygame.draw.line(self.screen, color, pos, (pos[0]-rel[0], pos[1]-rel[1]), 5)
self.x+= 1
if self.x>172: self.x=0
else:
if pos[0]<172:
if buttons[0]==1:
self.drawcolor= self.screen.get_at(pos)
pygame.draw.circle(self.screen, self.drawcolor, (250, 100), 30)
def draw(self):
pass
#self.screen.fill((255,255,255))
#pygame.draw.circle(self.screen, (0,0,0), (50,100), 20)
s = Starter()
s.mainLoop(40)
Here's a simplified version of Matthew's example which is unfortunately not runnable.
When the mouse is moved, pygame.MOUSEMOTION events are added to the event queue which contain the position and the relative movement. You can use these to calculate the previous position and then pass the two points to pygame.draw.line.
pygame.MOUSEMOTION events also have a buttons attribute which you can use to check which mouse button is currently down.
import os
import random
import pygame as pg
class App:
def __init__(self):
os.environ['SDL_VIDEO_CENTERED'] = '1'
pg.init()
self.w, self.h = 800, 600
self.screen = pg.display.set_mode((self.w, self.h))
self.screen.fill(pg.Color('white'))
self.clock = pg.time.Clock()
self.drawcolor = (0, 0, 0)
def mainloop(self):
while True:
for event in pg.event.get():
if event.type == pg.QUIT:
return
elif event.type == pg.MOUSEBUTTONDOWN:
if event.button == 2: # Color picker (middle mouse button).
self.drawcolor = self.screen.get_at(pos)
# Pick a random color.
# self.drawcolor = [random.randrange(256) for _ in range(3)]
elif event.type == pg.MOUSEMOTION:
pos, rel = event.pos, event.rel
if event.buttons[0]: # If the left mouse button is down.
# Draw a line from the pos to the previous pos.
pg.draw.line(self.screen, self.drawcolor, pos, (pos[0]-rel[0], pos[1]-rel[1]), 5)
elif event.buttons[2]: # If the right mouse button is down.
# Erase by drawing a circle.
pg.draw.circle(self.screen, (255, 255, 255), pos, 30)
pg.display.flip()
self.clock.tick(30)
if __name__ == '__main__':
app = App()
app.mainloop()
pg.quit()
来源：https://stackoverflow.com/questions/597369/how-to-create-ms-paint-clone-with-python-and-pygame