HTML canvas globalCompositeOperation模式的规范在哪里？

Question

最近，我一直在遍历数十亿字节的关于画布混合模式各个方面的博学论文，甚至发现了像这样的精美测试页。

但是，我只能在每个像素的基础上找到关于不同模式的模糊描述，包括在选择src / dest像素或组合src / dest值时使用alpha通道的方式。

请问一个善良的灵魂可以向我提供可靠的消息来源吗？

Answer 1

HTML5 canvas 2d上下文的正式规范由WhatWG和万维网联合会发布 。

WhatWG为复合操作值引用了单独的规范 。

W3对其定义如下：

source-atop
    A atop B. Display the source image wherever both images are opaque. Display the destination image wherever the destination image is opaque but the source image is transparent. Display transparency elsewhere.
source-in
    A in B. Display the source image wherever both the source image and destination image are opaque. Display transparency elsewhere.
source-out
    A out B. Display the source image wherever the source image is opaque and the destination image is transparent. Display transparency elsewhere.
source-over (default)
    A over B. Display the source image wherever the source image is opaque. Display the destination image elsewhere.
destination-atop
    B atop A. Same as source-atop but using the destination image instead of the source image and vice versa.
destination-in
    B in A. Same as source-in but using the destination image instead of the source image and vice versa.
destination-out
    B out A. Same as source-out but using the destination image instead of the source image and vice versa.
destination-over
    B over A. Same as source-over but using the destination image instead of the source image and vice versa.
lighter
    A plus B. Display the sum of the source image and destination image, with color values approaching 255 (100%) as a limit.
copy
    A (B is ignored). Display the source image instead of the destination image.
xor
    A xor B. Exclusive OR of the source image and destination image.
vendorName-operationName
    Vendor-specific extensions to the list of composition operators should use this syntax.