原文轉載自「劉悦的技術博客」https://v3u.cn/a_id_207
曾幾何時，SVG(Scalable Vector Graphics)矢量動畫圖被坊間稱之為一種被瀏覽器詛咒的技術，只因為糟糕的硬件支持(IE)，和沒完沒了的兼容性調優(Safari)。但是在2022年的今天，一切都不一樣了，正所謂三十年河東，三十年河西，微軟所研發的採用Chromium內核作為IE替代者的Edge瀏覽器已經有望超越Safari成為第二大桌面瀏覽器，而曾經因為不支持關鍵幀動畫被人詬病的Safari也統一了標準，市面上除了老幫菜IE，幾乎所有平台(包括移動端)都已經對SVG足夠友好，這讓我們可以放心大膽的在網站上應用SVG矢量動畫圖。
目前國內外相對來説技術先行的平台都已經採用SVG矢量格式，比如線上媒體界的巨擘Netflix、社交平台Twitter和國內的B站：
總的來説，採用SVG格式圖像的好處還是比較多的，由於 SVG 圖像是矢量圖像，可以無限縮放，而且在圖像質量下降方面沒有任何問題。為什麼會這樣呢？因為 SVG 圖像是使用 XML 標記構建的，瀏覽器通過繪製每個點和線來打印它們。這確保 SVG 圖像可以適應不同的屏幕大小和分辨率，傳統圖像格式（如 PNG、GIF 或 JPG）是通過預定義的像素來填充色彩空間，這就導致屏幕素質會對圖像的成像質量產生影響。
舉個例子，傳統像素圖片就像是食堂裏已經烙好的餅，是多大就是多大，碰上胃口好的，餅不夠大，就會產生影響，而SVG是通過XML技術把餅的輪廓和技術參數定義好，由瀏覽器實時繪製，可以根據胃口的大小自適應餅的大小，達到矢量的目的。同時，由於是在 XML 中定義的，SVG 圖像比 JPG 或 PNG 圖像更靈活，而且我們可以使用 CSS 和 JavaScript 與它們進行交互。另外從文件體積角度上講，SVG並不比PNG更大，反而壓縮之後體積更小，最後作為XML的網頁格式，直接在瀏覽器中解析，所以不需要單獨的帶寬進行請求，節約了網絡請求數，百利而無一害。
接下來的傳統節目應該是介紹SVG基本語法，然後畫幾個不痛不癢的簡單矢量圖，展現一下SVG特性，最後草草了事，那樣就太無趣了，本次我們來點“快餐”，簡單粗暴的將PNG的Logo圖像直接轉化成SVG格式，略過“繪製”的步驟，五分鐘內直接讓你的網站Logo“蕪湖起飛”。
SVG圖像轉化與壓縮
以本站的Logo為例子，首先需要一個PNG矢量圖：
注意圖像顏色位數最好越小越好，這樣轉化後的圖像不會過大，同時背景最好是透明的，因為透明元素不會被XML文件進行標記，達到節約空間的目的，這裏我們以PNG仿色4位的位圖為例子。
轉化方式有很多種，可以通過Python3的三方圖像庫:
pip3 install Pillow編寫轉化腳本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))運行腳本文件：
python3 test.py test.png將會直接產出同名的test.svg文件，利用vscode(安裝svg預覽控件)打開：
原理就是將原位圖的像素進行遍歷，轉化成SVG的Path路徑格式，每個位圖元素塊都會是單獨的一個Path標籤，如果不需要對某個單獨元素塊進行操作，也可以合併為一個path路徑標籤。
接下來，將轉化好的svg文件進行壓縮，壓縮後體積會相應的減小，同時一些path也可以被合併，通過npm安裝壓縮軟件svgo:
npm install -g svgo執行壓縮命令，test.svg是源文件，my.svg是壓縮後的文件：
svgo test.svg -o my.svg得到壓縮後的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 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5.082-10.588l2.669-8.629h-27.769l-1.965 6.556c-1.45 4.842-1.497 6.711-.176 7.151 1.288.43 1.338 1.883.179 5.209-2.181 6.257-4.094 5.799-5.3-1.269-.553-3.235-1.671-8.53-2.485-11.765l-1.481-5.882h-30.534l-2.442 9.371m-112.089 36.903c-.261.863-1.513 5.303-2.784 9.867l-2.311 8.299 11.835-.455 11.835-.456 2.105-7.059c3.515-11.782 3.528-11.764-9.027-11.764-6.149 0-11.393.706-11.653 1.568m-17.951 42.353c0 1.294.706 2.353 1.569 2.353.862 0 1.568-1.059 1.568-2.353 0-1.294-.706-2.353-1.568-2.353-.863 0-1.569 1.059-1.569 2.353m-121.274.229c-.594.593-1.079 5.549-1.079 11.013v9.935h7.059c4.716 0 7.059-.671 7.059-2.023 0-1.176-1.806-1.997-4.314-1.961-4.168.06-4.319-.227-4.465-8.485-.14-7.955-1.693-11.046-4.26-8.479m17.745 9.967c0 8.715.485 10.981 2.353 10.981 1.867 0 2.353-2.266 2.353-10.981 0-8.714-.486-10.98-2.353-10.98-1.868 0-2.353 2.266-2.353 10.98m9.411-3.137c0 12.177 9.456 18.732 16.228 11.249 3.493-3.859 3.687-19.092.243-19.092-1.765 0-2.353 1.882-2.353 7.529 0 8.705-2.181 11.917-6.515 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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>這裏我們將多個path路徑合併為一個，如果不想使用本地的代碼腳本進行轉化和壓縮，也可以利用線上對應的網絡工具，轉化svg：https://www.pngtosvg.com/ 壓縮svg: https://jakearchibald.github....
線上轉化效果和本地轉化效果大同小異。
SVG交互效果
事實上，直接將上面的代碼放到頁面中，就可以直接使用了，這裏通過指定svg的viewBox屬性裏面的4個座標來標定 svg 圖片的顯示區域，也就是我們理解的“畫布”，然後通過控制width屬性來實現等比的擴大和縮小，非常方便，效果是這樣的：
除了分辨率能夠適應屏幕顯得更加精細，其他的地方和傳統png好像沒有什麼不同？那麼就來點不一樣的吧，svg可以通過css樣式來實現“動畫”特效，比如描邊：
<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>這裏我們為path屬性加上偽類，同時通過stroke屬性為logo加上一層外邊框，透明度為0.2，寬度為7個像素，接着，編寫關鍵幀動畫：
@keyframes pinap {
to {
stroke-dashoffset: 0;
}
0% {fill-opacity: 0; }
100% {fill-opacity: 1; filter: drop-shadow(0px 0px 2px var(--logo-color));}
}頁面加載時，指定 stroke-dasharray 屬性進行描邊的路徑遍歷，同時將logo本體的顏色透明度由0至1進行遞增操作：
如果覺得意猶未盡，可以利用hover屬性，將鼠標對Logo進行懸停動作時再觸發一遍特效：
path.path:hover{
stroke-dasharray: 1000;
stroke-dashoffset: 1000;
animation: dash 3s linear forwards;
/* fill:white; */
fill-opacity: 1;
}還記得之前對於網站“暗黑模式”的實驗嗎？利用CSS3自定義屬性來為網站添加“暗黑模式”(暗色模式/DarkMode) 當時我們使用了自定義屬性，切換暗黑模式的同時切換另外一張暗色的Logo達到明亮和暗黑的效果，成本就是需要一明一暗兩張圖片配合使用，而現在，不需要多餘的圖片，只需要通過簡單的自定義顏色即可：
:root{--logo-color:#2b2b2b}
path.path{
fill:var(--logo-color);
}svg的fill屬性可以直接渲染圖片顏色：
簡單而又方便，還等什麼？拋棄落伍的PNG吧。
配合濾鏡，還可以打造霓虹燈特效：
filter: drop-shadow(0px 0px 2px var(--logo-color));
結語：“舊時王謝堂前燕，飛入尋常百姓家”，通過淘汰落後產能、上大壓小、加強技術革新，我們可以利用SVG技術打造成本更低，擴展性更高的圖像展示方案，何樂而不為？最後，奉上演示項目地址：https://github.com/zcxey2911/svg\_website\_logo，博君一曬。
原文轉載自「劉悦的技術博客」 https://v3u.cn/a_id_207
