如何使用 PIL 绘制箭头？

Question

我需要通过PIL画一个箭头。用户发送箭头的起点坐标和终点坐标。我没有任何想法。我怎样才能做到呢？

Answer 1

PIL 不提供绘制箭头的简单方法，因此我建议将PIL Image转换为NumPy数组，并使用OpenCV、Matplotlib、Cairo或Wand在其上绘制箭头，然后转换回PIL Image：#!/usr/bin/env python3import cv2import numpy as npfrom PIL import Image# Create an empty solid blue imagew, h = 640, 480im = Image.new('RGB', (w,h), (0,0,255))# Make into Numpy array so we can use OpenCV drawing functionsna = np.array(im)# Draw arrowed line, from 10,20 to w-40,h-60 in black with thickness 8 pixelsna = cv2.arrowedLine(na, (10,20), (w-40, h-60), (0,0,0), 8)# Revert back to PIL Image and saveImage.fromarray(na).save('result.png')请注意，OpenCV 使用 BGR 而不是 RGB 排序，因此如果您想要 PIL 中的红线，则需要在 OpenCV 中使用(0, 0, 255) 。如果您真的非常想使用PIL绘制带有箭头的线，您可以绘制一条线，然后在其末端添加一个三角形，draw.polygon()如下所示：#!/usr/bin/env python3import mathimport randomfrom PIL import Image, ImageDrawdef arrowedLine(im, ptA, ptB, width=1, color=(0,255,0)):    """Draw line from ptA to ptB with arrowhead at ptB"""    # Get drawing context    draw = ImageDraw.Draw(im)    # Draw the line without arrows    draw.line((ptA,ptB), width=width, fill=color)    # Now work out the arrowhead    # = it will be a triangle with one vertex at ptB    # - it will start at 95% of the length of the line    # - it will extend 8 pixels either side of the line    x0, y0 = ptA    x1, y1 = ptB    # Now we can work out the x,y coordinates of the bottom of the arrowhead triangle    xb = 0.95*(x1-x0)+x0    yb = 0.95*(y1-y0)+y0    # Work out the other two vertices of the triangle    # Check if line is vertical    if x0==x1:       vtx0 = (xb-5, yb)       vtx1 = (xb+5, yb)    # Check if line is horizontal    elif y0==y1:       vtx0 = (xb, yb+5)       vtx1 = (xb, yb-5)    else:       alpha = math.atan2(y1-y0,x1-x0)-90*math.pi/180       a = 8*math.cos(alpha)       b = 8*math.sin(alpha)       vtx0 = (xb+a, yb+b)       vtx1 = (xb-a, yb-b)    #draw.point((xb,yb), fill=(255,0,0))    # DEBUG: draw point of base in red - comment out draw.polygon() below if using this line    #im.save('DEBUG-base.png')              # DEBUG: save    # Now draw the arrowhead triangle    draw.polygon([vtx0, vtx1, ptB], fill=color)    return im# Create an empty solid blue imagew, h = 640, 480im = Image.new('RGB', (w,h), (0,0,255))# Get some controlled randomnessrandom.seed(58)# Draw some random arrowsfor _ in range(10):    ptA = (random.randint(0,w), random.randint(0,h))    ptB = (random.randint(0,w), random.randint(0,h))    im = arrowedLine(im, ptA, ptB)# Saveim.save('result.png')关键词：Python、图像处理、PIL、Pillow、箭头、箭头、箭头线、OpenCV。