Canvas Clipping Test

This demo tests whether the strokes of shapes in HTML5 Canvas can serve as clipping areas for subsequent drawings. The specific questions:

Can a thick line's stroke itself be used as a clipping path?
Can a rectangle's stroke be used as a clipping path?

You can edit the code for each test directly in the textareas below and click "Run Test" to see the results.

Test 1: Standard Line Clipping Attempt

Here we try to use a line's stroke directly as a clipping path:

Test 2: Alternative Approach

Try different approaches to clipping with line strokes:

Test 3: Rectangle with Stroke

Testing if a rectangle's stroke is used as a clipping path (it isn't):

Conclusion

Experiment with different approaches by modifying the code above. The tests demonstrate that neither line strokes nor rectangle strokes can be directly used as clipping paths - only the mathematical path (with no thickness) is used for clipping.

Key observations:

Test 1 shows that when clipping to a line, only the infinitely thin mathematical line is used as the clipping path, not the visible stroke.
Test 2 demonstrates a workaround by creating a rectangular clipping path that matches the line's stroke dimensions.
Test 3 confirms that even with rectangles, the clipping path only follows the rectangle's path outline, not including its stroke area.

Alternative approaches might include:

Creating a rectangle or polygon that surrounds the line or shape
Using multiple line segments to create a closed path
Using other Canvas techniques like compositing operations

Canvas Clipping Test: Shape Strokes as Clipping Areas

Test 1: Standard Line Clipping Attempt

Test 2: Alternative Approach

Test 3: Rectangle with Stroke

Conclusion