Understanding and application of SVG Path path parameters: Why is the end coordinate -.1 0 instead of 0 0, and what is the difference between using lowercase letters a and z?

Deeply understand SVG Path Parameters and Applications

SVG paths (Path) are powerful tools in SVG drawings, but the understanding and application of their parameters are often confusing. This article will use code snippets as an example to explain in detail the meaning and usage techniques of SVG Path parameters.

Code snippet:

 <code>offset: path("M 100,0 a 100 100 0 1 1 -.1 0 z");</code>

We will analyze the -.1 0 coordinates and the reasons for the use of upper and lowercase letters a and z .

SVG Path Command Overview

First, let’s review the commonly used SVG Path commands:

• M xy : Move the brush to coordinates (x, y) .
• L xy : draw lines from the current position to coordinates (x, y) .
• H x : draw the line horizontally to the x coordinate.
• V y : draw lines vertically to y coordinates.
• Z or z : Close the path, connected to the starting point.
• C x1 y1, x2 y2, xy or c dx1 dy1, dx2 dy2, dx dy : cubic Bezier curve.
• Q x1 y1, xy or q dx1 dy1, dx dy : Quadratic Bezier curve.
• A rx ry x-axis-rotation large-arc-flag sweep-flag xy or a rx ry x-axis-rotation large-arc-flag sweep-flag dx dy : elliptical arc.

Code Analysis

Let's analyze the code one by one:

• M 100,0 : Move the brush to point (100, 0) .
• a 100 100 0 1 1 -.1 0 : Draw an ellipse arc. The parameters are as follows:
  • 100 100 : The x-radius and y-radius of the ellipse.
  • 0 : The rotation angle of the x-axis (0 degrees).
  • 1 : Large arc mark (1 means drawing a large arc).
  • 1 : Scan the flag (1 indicates clockwise).
  • -.1 0 : The end point coordinate of the arc, the offset relative to the starting point.
• z : Close the path and connect to the starting point.

-.1 0

Why is the end coordinate -.1 0 instead of 0 0 ? This is because if the start and end points exactly coincide, the SVG renderer may not be able to interpret this arc path correctly. -.1 0 is a tiny offset that ensures that the path is valid while having little effect on the visual effect.

The difference between upper and lower case letters a and z

• The lowercase letter a means drawing an ellipse arc using relative coordinates. -.1 0 is the offset relative to the starting point (100, 0) , and the actual end point coordinate is (99.9, 0) .
• The lowercase letter z indicates a closed path. There is no difference between Z and z in function, it is just that Z uses absolute coordinates, while z uses relative coordinates, but the z command itself does not involve coordinates.

Through the above analysis, we have a clearer understanding of the meaning of SVG Path parameters and how to apply them. Mastering these details can create complex SVG graphics more efficiently.

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