w3c / w3c/csswg-drafts

[css-easing-1] Extrapolation of easing function

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css-easing-1
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Description

https://www.w3.org/TR/css-easing-1/#cubic-bezier-algo

For input progress < 0:
Point #2 implies that the tangent line though P0 and P2 should be used in the event that P1_x = 0 and P2_x > 0. This should be further constrained on P1_y = 0. It is only a valid tangent line if P1 and P0 are coincident.

If P0, P1 and P2 are all coincident. The tangent line should be through P0 and P3.

For input progress > 1:
Point #2 implies that the tangent line through P1 and P3 should be used in the event that P2_x = 1 and P1_x < 1. This should be further constrained on P2_y = 1. It is only a valid tangent line if P2 and P3 are coincident.

If P1, P2, and P3 are all coincident. The tangent line should be through P0 and P3.

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Read the CSS Easing Level 1 cubic-bezier algorithm at the linked specification section, focusing on the extrapolation rules for input progress below 0 and above 1. Compare the stated tangent-line conditions with the coincident-point cases described in the issue; done means the algorithm's constraints and fallback lines are resolved and reflected in the specification.

Written by the indexing model from the issue text.

Assessment

Tech stack
css
Domain
documentation, web-dev
Issue type
Bug
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
25/100

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