原文转载自「刘悦的技术博客」https://v3u.cn/a_id_207
曾几何时，SVG(Scalable Vector Graphics)矢量动画图被坊间称之为一种被浏览器诅咒的技术，只因为糟糕的硬件支持(IE)，和没完没了的兼容性调优(Safari)。但是在2022年的今天，一切都不一样了，正所谓三十年河东，三十年河西，微软所研发的采用Chromium内核作为IE替代者的Edge浏览器已经有望超越Safari成为第二大桌面浏览器，而曾经因为不支持关键帧动画被人诟病的Safari也统一了标准，市面上除了老帮菜IE，几乎所有平台(包括移动端)都已经对SVG足够友好，这让我们可以放心大胆的在网站上应用SVG矢量动画图。
目前国内外相对来说技术先行的平台都已经采用SVG矢量格式，比如线上媒体界的巨擘Netflix、社交平台Twitter和国内的B站：
总的来说，采用SVG格式图像的好处还是比较多的，由于 SVG 图像是矢量图像，可以无限缩放，而且在图像质量下降方面没有任何问题。为什么会这样呢？因为 SVG 图像是使用 XML 标记构建的，浏览器通过绘制每个点和线来打印它们。这确保 SVG 图像可以适应不同的屏幕大小和分辨率，传统图像格式（如 PNG、GIF 或 JPG）是通过预定义的像素来填充色彩空间，这就导致屏幕素质会对图像的成像质量产生影响。
举个例子，传统像素图片就像是食堂里已经烙好的饼，是多大就是多大，碰上胃口好的，饼不够大，就会产生影响，而SVG是通过XML技术把饼的轮廓和技术参数定义好，由浏览器实时绘制，可以根据胃口的大小自适应饼的大小，达到矢量的目的。同时，由于是在 XML 中定义的，SVG 图像比 JPG 或 PNG 图像更灵活，而且我们可以使用 CSS 和 JavaScript 与它们进行交互。另外从文件体积角度上讲，SVG并不比PNG更大，反而压缩之后体积更小，最后作为XML的网页格式，直接在浏览器中解析，所以不需要单独的带宽进行请求，节约了网络请求数，百利而无一害。
接下来的传统节目应该是介绍SVG基本语法，然后画几个不痛不痒的简单矢量图，展现一下SVG特性，最后草草了事，那样就太无趣了，本次我们来点“快餐”，简单粗暴的将PNG的Logo图像直接转化成SVG格式，略过“绘制”的步骤，五分钟内直接让你的网站Logo“芜湖起飞”。
SVG图像转化与压缩
以本站的Logo为例子，首先需要一个PNG矢量图：
注意图像颜色位数最好越小越好，这样转化后的图像不会过大，同时背景最好是透明的，因为透明元素不会被XML文件进行标记，达到节约空间的目的，这里我们以PNG仿色4位的位图为例子。
转化方式有很多种，可以通过Python3的三方图像库:
pip3 install Pillow
编写转化脚本test.py：
import sys
import os
import operator
from collections import deque
import io
from optparse import OptionParser
from PIL import Image
def add_tuple(a, b):
return tuple(map(operator.add, a, b))
def sub_tuple(a, b):
return tuple(map(operator.sub, a, b))
def neg_tuple(a):
return tuple(map(operator.neg, a))
def direction(edge):
return sub_tuple(edge[1], edge[0])
def magnitude(a):
return int(pow(pow(a[0], 2) + pow(a[1], 2), .5))
def normalize(a):
mag = magnitude(a)
assert mag > 0, "Cannot normalize a zero-length vector"
return tuple(map(operator.truediv, a, [mag] * len(a)))
def svg_header(width, height):
return """<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN"
"http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<svg width="%d" height="%d"
xmlns="http://www.w3.org/2000/svg" version="1.1">
""" % (width, height)
def rgba_image_to_svg_pixels(im):
s = io.StringIO()
s.write(svg_header(*im.size))
width, height = im.size
for x in range(width):
for y in range(height):
here = (x, y)
rgba = im.getpixel(here)
if not rgba[3]:
continue
s.write(
""" <rect x="%d" y="%d" width="1" height="1" style="fill:rgb%s; fill-opacity:%.3f; stroke:none;" />\n"""
% (x, y, rgba[0:3], float(rgba[3]) / 255))
print("Converting pixels: " + str(x * 100 / width) + "%")
s.write("""</svg>\n""")
return s.getvalue()
def joined_edges(assorted_edges, keep_every_point=False):
pieces = []
piece = []
directions = deque([
(0, 1),
(1, 0),
(0, -1),
(-1, 0),
])
while assorted_edges:
if not piece:
piece.append(assorted_edges.pop())
current_direction = normalize(direction(piece[-1]))
while current_direction != directions[2]:
directions.rotate()
for i in range(1, 4):
next_end = add_tuple(piece[-1][1], directions[i])
next_edge = (piece[-1][1], next_end)
if next_edge in assorted_edges:
assorted_edges.remove(next_edge)
if i == 2 and not keep_every_point:
# same direction
piece[-1] = (piece[-1][0], next_edge[1])
else:
piece.append(next_edge)
if piece[0][0] == piece[-1][1]:
if not keep_every_point and normalize(direction(
piece[0])) == normalize(direction(piece[-1])):
piece[-1] = (piece[-1][0], piece.pop(0)[1])
# same direction
pieces.append(piece)
piece = []
break
else:
raise Exception("Failed to find connecting edge")
return pieces
def rgba_image_to_svg_contiguous(im, keep_every_point=False):
# collect contiguous pixel groups
adjacent = ((1, 0), (0, 1), (-1, 0), (0, -1))
visited = Image.new("1", im.size, 0)
color_pixel_lists = {}
width, height = im.size
for x in range(width):
for y in range(height):
here = (x, y)
if visited.getpixel(here):
continue
rgba = im.getpixel((x, y))
if not rgba[3]:
continue
piece = []
queue = [here]
visited.putpixel(here, 1)
while queue:
here = queue.pop()
for offset in adjacent:
neighbour = add_tuple(here, offset)
if not (0 <= neighbour[0] <
width) or not (0 <= neighbour[1] < height):
continue
if visited.getpixel(neighbour):
continue
neighbour_rgba = im.getpixel(neighbour)
if neighbour_rgba != rgba:
continue
queue.append(neighbour)
visited.putpixel(neighbour, 1)
piece.append(here)
if not rgba in color_pixel_lists:
color_pixel_lists[rgba] = []
color_pixel_lists[rgba].append(piece)
print("Converting image: " + str(round(x * 100 / width, 2)) + "%")
del adjacent
del visited
# calculate clockwise edges of pixel groups
edges = {
(-1, 0): ((0, 0), (0, 1)),
(0, 1): ((0, 1), (1, 1)),
(1, 0): ((1, 1), (1, 0)),
(0, -1): ((1, 0), (0, 0)),
}
color_edge_lists = {}
counter = 0
for rgba, pieces in color_pixel_lists.items():
for piece_pixel_list in pieces:
edge_set = set([])
for coord in piece_pixel_list:
for offset, (start_offset, end_offset) in edges.items():
neighbour = add_tuple(coord, offset)
start = add_tuple(coord, start_offset)
end = add_tuple(coord, end_offset)
edge = (start, end)
if neighbour in piece_pixel_list:
continue
edge_set.add(edge)
if not rgba in color_edge_lists:
color_edge_lists[rgba] = []
color_edge_lists[rgba].append(edge_set)
counter = counter + 1
print("Calculating edges: " +
str(round(counter * 100 / len(color_pixel_lists.items()), 2)) +
"%")
del color_pixel_lists
del edges
# join edges of pixel groups
color_joined_pieces = {}
for color, pieces in color_edge_lists.items():
color_joined_pieces[color] = []
for assorted_edges in pieces:
color_joined_pieces[color].append(
joined_edges(assorted_edges, keep_every_point))
s = io.StringIO()
s.write(svg_header(*im.size))
counter = 0
for color, shapes in color_joined_pieces.items():
for shape in shapes:
s.write(""" <path d=" """)
for sub_shape in shape:
here = sub_shape.pop(0)[0]
s.write(""" M %d,%d """ % here)
for edge in sub_shape:
here = edge[0]
s.write(""" L %d,%d """ % here)
s.write(""" Z """)
s.write(
""" " style="fill:rgb%s; fill-opacity:%.3f; stroke:none;" />\n"""
% (color[0:3], float(color[3]) / 255))
counter = counter + 1
print("Joining edges: " +
str(round(counter * 100 / len(color_joined_pieces.items()), 2)) +
"%")
s.write("""</svg>\n""")
return s.getvalue()
def png_to_svg(filename, contiguous=None, keep_every_point=None):
try:
im = Image.open(filename)
except IOError as e:
sys.stderr.write('%s: Could not open as image file\n' % filename)
sys.exit(1)
im_rgba = im.convert('RGBA')
if contiguous:
return rgba_image_to_svg_contiguous(im_rgba, keep_every_point)
else:
return rgba_image_to_svg_pixels(im_rgba)
if __name__ == "__main__":
parser = OptionParser()
parser.add_option(
"-p",
"--pixels",
action="store_false",
dest="contiguous",
help=
"Generate a separate shape for each pixel; do not group pixels into contiguous areas of the same colour",
default=True)
parser.add_option(
"-1",
"--one",
action="store_true",
dest="keep_every_point",
help=
"1-pixel-width edges on contiguous shapes; default is to remove intermediate points on straight line edges. ",
default=None)
(options, args) = parser.parse_args()
if (len(sys.argv)) < 2:
for file in os.listdir("."):
if file.endswith(".png"):
print("Converting " + file)
f = open(file.replace(".png", ".svg"), 'w')
f.write(
png_to_svg(file,
contiguous=options.contiguous,
keep_every_point=options.keep_every_point))
else:
for file in sys.argv:
if file.endswith(".png"):
print("Converting " + file)
f = open(file.replace(".png", ".svg"), 'w')
f.write(
png_to_svg(file,
contiguous=options.contiguous,
keep_every_point=options.keep_every_point))
运行脚本文件：
python3 test.py test.png
将会直接产出同名的test.svg文件，利用vscode(安装svg预览控件)打开：
原理就是将原位图的像素进行遍历，转化成SVG的Path路径格式，每个位图元素块都会是单独的一个Path标签，如果不需要对某个单独元素块进行操作，也可以合并为一个path路径标签。
接下来，将转化好的svg文件进行压缩，压缩后体积会相应的减小，同时一些path也可以被合并，通过npm安装压缩软件svgo:
npm install -g svgo
执行压缩命令，test.svg是源文件，my.svg是压缩后的文件：
svgo test.svg -o my.svg
得到压缩后的svg:
<svg xmlns="http://www.w3.org/2000/svg" width="250" viewBox="0 0 400 313.725">
<path d="M231.828 11.305c-3.763 2.949-7.266 3.479-30.517 4.623-46.344 2.278-61.703 11.6-61.703 37.45v9.581l4.839-3.636c7.122-5.353 14.345-8.975 17.906-8.982 2.225-.005 1.454.883-2.652 3.051-8.485 4.482-31.488 27.939-35.476 36.176-9.856 20.362.264 32.59 30.95 37.395 10.341 1.619 13.209 3.617 11.781 8.208-5.166 16.617 80.367 23.977 87.191 7.503 2.614-6.311.889-11.626-5.131-15.81-2.802-1.948-9.967-7.7-15.923-12.784-14.324-12.226-19.669-14.14-31.915-11.43-4.296.951-4.944.731-4.127-1.399.812-2.117-.114-2.455-5.715-2.085-9.411.622-9.816-2.778-.483-4.057 5.39-.739 8.043-.415 9.634 1.176 1.428 1.428 4.214 1.925 7.969 1.421 7.532-1.01 14.472 2.028 25.819 11.301l9.177 7.5 8.078-1.812c24.986-5.605 33.798-15.992 30.135-35.52-4.175-22.251-53.429-34.124-83.234-20.063l-4.706 2.22 3.717-3.226c13.698-11.889 56.459-11.57 74.326.555 6.558 4.45 7.448 3.51 7.448-7.864 0-18.854-18.5-23.967-61.832-17.088-17.292 2.744-31.119 2.595-34.083-.369-1.105-1.105.531-1.381 5.19-.876 3.742.405 15.189-.734 25.438-2.531 10.249-1.796 22.072-3.266 26.274-3.266 9.076 0 10.213-3.562 4.056-12.699-4.358-6.466-6.887-7.008-12.431-2.663M215.737 130.9c6.031 2.521 7.046 6.169 2.405 8.653-7.504 4.016-17.052-2.06-12.003-7.639 3.538-3.909 2.844-3.836 9.598-1.014m-5.541 3.125c0 2.208.706 4.014 1.569 4.014.862 0 1.568-1.37 1.568-3.044 0-1.675-.706-3.481-1.568-4.015-.89-.549-1.569.768-1.569 3.045M5.839 203.529c-1.456 5.21-1.896 9.241-1.042 9.543.832.294 1.478 10.421 1.478 23.184v22.661l19.933-.439 19.933-.439 12.084-21.096c6.647-11.602 13.134-21.863 14.416-22.8 1.765-1.29 7.359-15.836 7.359-19.134 0-.274-6.686-.499-14.858-.499H50.284l-2.439 8.389c-1.342 4.614-2.02 9.482-1.508 10.817 1.026 2.672-8.309 22.482-9.862 20.929-1.831-1.831-.255-18.929 1.898-20.591 1.163-.899 2.926-4.649 3.918-8.334.992-3.685 2.194-7.715 2.67-8.955.722-1.883-2.223-2.255-17.868-2.255H8.359l-2.52 9.019m88.643-7.092c-4.02 1.937-8.873 9.28-10.389 15.72l-1.016 4.314h11.689c10.312 0 11.807-.37 12.685-3.138.995-3.134 2.585-3.951 4.316-2.219 2.318 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7.117-3.553-2.353-4.098l-8.236-.474v11.062m33.855-8.834c-4.079 2.983-2.494 7.781 3.433 10.39 7.54 3.318 4.217 7.372-3.798 4.633-.992-.339-2.051.072-2.352.914-.825 2.3 7.059 4.556 11.779 3.371 5.827-1.463 6.039-9.856.285-11.3-2.122-.532-4.672-1.949-5.667-3.149-2.507-3.02 1.892-4.623 6.264-2.283 2.594 1.388 3.26 1.287 3.26-.495 0-4.216-8.461-5.549-13.204-2.081m28.89 8.916v10.981h6.147c9.758 0 15.815-6.318 9.687-10.105-.782-.483-1.025-2.395-.54-4.249 1.136-4.346-3.195-7.607-10.103-7.607h-5.191v10.98m23.53 0v10.981h6.274c4.076 0 6.275-.709 6.275-2.023 0-1.176-1.806-1.997-4.314-1.961-4.159.06-4.33-.26-4.784-8.957-.668-12.8-3.451-11.219-3.451 1.96m20.304-8.087c-2.416 1.956-3.572 4.574-3.572 8.087 0 9.948 12.212 14.654 19.073 7.35 9.723-10.35-4.406-24.421-15.501-15.437m26.868 1.24c-7.54 9.587 1.045 20.207 13.612 16.839 4.862-1.303 5.249-11.163.424-10.807-4.346.32-5.861 2.278-3.124 4.038 2.027 1.303 2.022 1.667-.036 2.989-3.051 1.96-8.465-1.512-9.118-5.848-.677-4.496 5.425-8.61 9.52-6.418 3.969 2.124 7.98-1.06 4.282-3.399-4.707-2.976-12.149-1.729-15.56 2.606m-15.121 2.025c5.815 6.425-2.308 15.742-8.407 9.643-4.05-4.05-4.068-5.573-.115-9.527 3.899-3.898 5.085-3.915 8.522-.116m-44.6.901c0 1.307-1.395 2.353-3.137 2.353-1.743 0-3.138-1.046-3.138-2.353 0-1.307 1.395-2.353 3.138-2.353 1.742 0 3.137 1.046 3.137 2.353m1.363 7.595c2.196 2.647.744 4.169-3.978 4.169-2.614 0-3.66-.896-3.66-3.137 0-3.647 4.916-4.311 7.638-1.032" />
</svg>
这里我们将多个path路径合并为一个，如果不想使用本地的代码脚本进行转化和压缩，也可以利用线上对应的网络工具，转化svg：https://www.pngtosvg.com/ 压缩svg: https://jakearchibald.github.io/svgomg/
线上转化效果和本地转化效果大同小异。
SVG交互效果
事实上，直接将上面的代码放到页面中，就可以直接使用了，这里通过指定svg的viewBox属性里面的4个坐标来标定 svg 图片的显示区域，也就是我们理解的“画布”，然后通过控制width属性来实现等比的扩大和缩小，非常方便，效果是这样的：
除了分辨率能够适应屏幕显得更加精细，其他的地方和传统png好像没有什么不同？那么就来点不一样的吧，svg可以通过css样式来实现“动画”特效，比如描边：
<svg xmlns="http://www.w3.org/2000/svg" width="250" viewBox="0 0 400 313.725">
<path class="path" stroke-opacity="0.2" stroke-width="7" stroke="black" d="M231.828 11.305c-3.763 2.949-7.266 3.479-30.517 4.623-46.344 2.278-61.703 11.6-61.703 37.45v9.581l4.839-3.636c7.122-5.353 14.345-8.975 17.906-8.982 2.225-.005 1.454.883-2.652 3.051-8.485 4.482-31.488 27.939-35.476 36.176-9.856 20.362.264 32.59 30.95 37.395 10.341 1.619 13.209 3.617 11.781 8.208-5.166 16.617 80.367 23.977 87.191 7.503 2.614-6.311.889-11.626-5.131-15.81-2.802-1.948-9.967-7.7-15.923-12.784-14.324-12.226-19.669-14.14-31.915-11.43-4.296.951-4.944.731-4.127-1.399.812-2.117-.114-2.455-5.715-2.085-9.411.622-9.816-2.778-.483-4.057 5.39-.739 8.043-.415 9.634 1.176 1.428 1.428 4.214 1.925 7.969 1.421 7.532-1.01 14.472 2.028 25.819 11.301l9.177 7.5 8.078-1.812c24.986-5.605 33.798-15.992 30.135-35.52-4.175-22.251-53.429-34.124-83.234-20.063l-4.706 2.22 3.717-3.226c13.698-11.889 56.459-11.57 74.326.555 6.558 4.45 7.448 3.51 7.448-7.864 0-18.854-18.5-23.967-61.832-17.088-17.292 2.744-31.119 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1.96-8.465-1.512-9.118-5.848-.677-4.496 5.425-8.61 9.52-6.418 3.969 2.124 7.98-1.06 4.282-3.399-4.707-2.976-12.149-1.729-15.56 2.606m-15.121 2.025c5.815 6.425-2.308 15.742-8.407 9.643-4.05-4.05-4.068-5.573-.115-9.527 3.899-3.898 5.085-3.915 8.522-.116m-44.6.901c0 1.307-1.395 2.353-3.137 2.353-1.743 0-3.138-1.046-3.138-2.353 0-1.307 1.395-2.353 3.138-2.353 1.742 0 3.137 1.046 3.137 2.353m1.363 7.595c2.196 2.647.744 4.169-3.978 4.169-2.614 0-3.66-.896-3.66-3.137 0-3.647 4.916-4.311 7.638-1.032" />
</svg>
这里我们为path属性加上伪类，同时通过stroke属性为logo加上一层外边框，透明度为0.2，宽度为7个像素，接着，编写关键帧动画：
@keyframes pinap {
to {
stroke-dashoffset: 0;
}
0% {fill-opacity: 0; }
100% {fill-opacity: 1; filter: drop-shadow(0px 0px 2px var(--logo-color));}
}
页面加载时，指定 stroke-dasharray 属性进行描边的路径遍历，同时将logo本体的颜色透明度由0至1进行递增操作：
如果觉得意犹未尽，可以利用hover属性，将鼠标对Logo进行悬停动作时再触发一遍特效：
path.path:hover{
stroke-dasharray: 1000;
stroke-dashoffset: 1000;
animation: dash 3s linear forwards;
/* fill:white; */
fill-opacity: 1;
}
还记得之前对于网站“暗黑模式”的实验吗？利用CSS3自定义属性来为网站添加“暗黑模式”(暗色模式/DarkMode) 当时我们使用了自定义属性，切换暗黑模式的同时切换另外一张暗色的Logo达到明亮和暗黑的效果，成本就是需要一明一暗两张图片配合使用，而现在，不需要多余的图片，只需要通过简单的自定义颜色即可：
:root{--logo-color:#2b2b2b}
path.path{
fill:var(--logo-color);
}
svg的fill属性可以直接渲染图片颜色：
简单而又方便，还等什么？抛弃落伍的PNG吧。
配合滤镜，还可以打造霓虹灯特效：
filter: drop-shadow(0px 0px 2px var(--logo-color));
结语：“旧时王谢堂前燕，飞入寻常百姓家”，通过淘汰落后产能、上大压小、加强技术革新，我们可以利用SVG技术打造成本更低，扩展性更高的图像展示方案，何乐而不为？最后，奉上演示项目地址：https://github.com/zcxey2911/svg_website_logo，博君一晒。
原文转载自「刘悦的技术博客」 https://v3u.cn/a_id_207