| Index: third_party/WebKit/Source/core/layout/README.md
|
| diff --git a/third_party/WebKit/Source/core/layout/README.md b/third_party/WebKit/Source/core/layout/README.md
|
| index 258a06d70ddd72d6598f8d012294b1ad005da364..4cdf2f0b60212fb25e0e5e295d2d77a349df3093 100644
|
| --- a/third_party/WebKit/Source/core/layout/README.md
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| +++ b/third_party/WebKit/Source/core/layout/README.md
|
| @@ -11,50 +11,48 @@ following document lifecycle states:
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| Note that a new Blink layout system is under development. See the
|
| [LayoutNG design document](https://docs.google.com/document/d/1uxbDh4uONFQOiGuiumlJBLGgO4KDWB8ZEkp7Rd47fw4/preview).
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|
|
| -## Overflow rects and scroll offsets
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| -
|
| -PaintLayerScrollableArea uses a "scroll origin" to conceptually represent the distance between
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| -the top-left corner of the box'es content rect and the top-left corner of its overflow rect
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| -when the box is scrolled to the logical beginning of its content (e.g. all the way to the left for
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| -LTR, all the way to the right for RTL). For left-to-right and top-to-bottom flows, the scroll
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| -origin is zero, i.e., the top/left of the overflow rect is at the same position as the top/left of
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| -the box'es content rect when scrolled to the beginning of flow. For right-to-left and bottom-to-top
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| -flows, the overflow rect extends to the top/left of the client rect.
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| -
|
| -The default calculation for scroll origin is the distance between the top-left corner of the content
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| -rect and the top-left corner of the overflow rect. To illustrate, here is a box with left overflow and
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| -no vertical scrollbar:
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| -
|
| - content
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| - rect
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| - |<-------->|
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| - scroll
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| - origin
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| - |<-------->|
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| - _____________________
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| - | | |
|
| - | | |
|
| - | | |
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| - direction:rtl | | box |
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| - | | |
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| - | | |
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| - |__________|__________|
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| +## Overflow and scrolling
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|
|
| - overflow rect
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| - |<--------------------->|
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| +When a LayoutBox has scrollable overflow, it is associated with a PaintLayerScrollableArea.
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| +PaintLayerScrollableArea uses a "scroll origin" to represent the location of the top/left
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| +corner of the content rect (the visible part of the content) in the coordinate system
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| +defined by the top/left corner of the overflow rect, when the box is scrolled all the way
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| +to the beginning of its content.
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| +
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| +For content which flows left-to-right and top-to-bottom, the scroll origin will be (0, 0),
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| +i.e., the top/left of the content rect is coincident with the top/left of the overflow rect
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| +when the box is scrolled all the way to the beginning of content.
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| +
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| +For content which flows right-to-left (including direction:ltr, writing-mode:vertical-rl,
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| +and flex-direction:row-reverse), the x-coordinate of the scroll origin will be positive;
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| +and for content which flows bottom-to-top (e.g., flex-direction:column-reverse and
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| +vertical writing-mode with direction:ltr), the y-coordinate of the scroll origin will be
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| +positive.
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| +
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| +In all cases, the term 'scrollOffset' (or just 'offset') is used to represent the distance
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| +of the scrolling viewport from its location when scrolled to the beginning of content, and
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| +it uses type ScrollOffset. The term 'scrollPosition' (or just 'position') represents a
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| +point in the coordinate space defined by the overflow rect, and it uses type FloatPoint.
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| +
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| +For illustrations of these concepts, see these files:
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|
|
| +doc/ltr-tb-scroll.png
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| +doc/rtl-bt-scroll.png
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| +doc/rtl-tb-scroll.png
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| +
|
| +When computing the scroll origin, if the box is laid out right-to-left and it has a scrollbar
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| +for the orthogonal direction (e.g., a vertical scrollbar in a direction:rtl block), the size
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| +of the scrollbar must be added to the scroll origin calculation. Here are two examples --
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| +note that it doesn't matter whether the vertical scrollbar is placed on the right or left of
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| +the box (the vertical scrollbar is the `|/|` part):
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|
|
| -However, if the box has a scrollbar for the orthogonal direction (e.g., a vertical scrollbar
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| -in a direction:rtl block), the size of the scrollbar must be added to the scroll origin calculation.
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| -Here are two examples -- note that it doesn't matter whether the vertical scrollbar is placed on
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| -the right or left of the box (the vertical scrollbar is the `|/|` part):
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|
|
| content
|
| rect
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| |<-------->|
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| scroll
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| origin
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| - |<---------->|
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| + |----------->|
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| _______________________
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| | |/| |
|
| | |/| |
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| @@ -63,29 +61,28 @@ the right or left of the box (the vertical scrollbar is the `|/|` part):
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| | |/| |
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| | |/| |
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| |__________|/|__________|
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| +
|
| + overflow rect
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| + |<--------------------->|
|
|
|
| + content
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| + rect
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| + |<-------->|
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| + scroll
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| + origin
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| + |----------->|
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| + _________________________
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| + | | |/|
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| + | | |/|
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| + | | |/|
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| + writing-mode: | | box |/|
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| + vertical-rl | | |/|
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| + | | |/|
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| + |____________|__________|/|
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| +
|
| overflow rect
|
| |<--------------------->|
|
|
|
| - content
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| - rect
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| - |<-------->|
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| - scroll
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| - origin
|
| - |<---------->|
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| - _______________________
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| - | | |/|
|
| - | | |/|
|
| - | | |/|
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| - writing-mode: | | |/|
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| - vertical-rl | | |/|
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| - | | |/|
|
| - | | |/|
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| - | | |/|
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| - |__________|__________|/|
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| -
|
| - overflow rect
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| - |<--------------------->|
|
|
|
| ## Coordinate Spaces
|
|
|
|
|
Chromium Code Reviews
Issue 2387883002:
Use float for scroll offset. (Closed)
