Canvas globalCompositeOperation：蒙版仅作用于红蓝图层，紫色图层仍受影响求助

Hey there! I took a look at your issue where the purple layer is still being affected by the mask meant only for red and blue, even though the orange layer is working correctly. The root problem here is mask scope—right now, your mask is probably applied to a parent element that includes the purple layer, or the purple layer is nested within the same container as the red/blue layers.

Here's the fix: #

We need to wrap just the red and blue layers in a dedicated group (<g>) and apply the mask only to that group. This way, the mask's effect is limited strictly to the layers inside the group, leaving purple and orange completely untouched.

Corrected SVG Code Example #

<svg width="400" height="400">
  <!-- Define your mask -->
  <mask id="mask">
    <rect x="50" y="50" width="200" height="200" fill="white"/>
  </mask>

  <!-- Group red and blue layers with the mask applied -->
  <g mask="url(#mask)">
    <rect x="0" y="0" width="150" height="150" fill="red"/>
    <rect x="100" y="100" width="150" height="150" fill="blue"/>
  </g>

  <!-- Purple and orange layers stay outside the masked group -->
  <rect x="200" y="0" width="150" height="150" fill="purple"/>
  <rect x="0" y="200" width="150" height="150" fill="orange"/>
</svg>

What Changed? #

• I created a <g> element and set its mask attribute to your existing mask ID. All red/blue layers are moved inside this group.
• The purple and orange layers are kept as direct children of the SVG, not inside the masked group. This ensures the mask never touches them.

This structure guarantees that your mask only affects the red and blue layers, while purple and orange render exactly as they should—no unintended masking!

内容的提问来源于stack exchange，提问作者zaarr78