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105 lines
4.9 KiB
105 lines
4.9 KiB
Coordinate systems
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==================
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This is fun; brace yourself
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Document:
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All objects have a position on the page which is described in the typographic units
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named points.
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There are 72 points to the inch, and these absolute coordinates simply place your
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objects on the page.
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An example; a frame is positioned on paper some 35mm from the left border of the paper and
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some 35mm from the top of the first page. the absolute position of that frame is 100, 100
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since 100pt equals 35mm.
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Note that positioning is done from page 1, so when a frame is moved from page 1 to page 2 it
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simply gets a higher Y coordinate.
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Zoomed: (aka Normal)
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Every object on screen has a size, and at different zoom levels we use a different amount
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of pixels to display the same object.
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Our object above has a top-left position of document:(100,100). To determine where
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this is on screen we call KoZoomHander::zoomItX(xPos) and KoZoomHander::zoomItY(yPos) to
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retrieve the pixel positioning on screen at the current zoom level. The zoom level
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is stored only in the zoomhandler, which is in KWord the document (an instance of KWDocument).
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Since we are using pixel values all these values are stored in integers, they should not
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be used to move something around, the absolute coordinate system has to be used for that.
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Internal:
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The former two were mostly for objects like frames etc, not for text. Text (the individual
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words and characters) are positioned with the tqlayout coordinates. Layout is similar to the
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Zoomed system, but always uses the same resolution. This resolution is sufficiently high to
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do the tqlayout in integers, and not really lose info.
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This is the high-resolution unit in which the text tqlayout is done,
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currently set to 1440 DPI. Everything known the QRT classes will be in
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this coordinate system (including the QTextFormats). When painting, we apply
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the current zoom and resolution to find the right font size to use, and we
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have to catch up with rounding differences. However the position of the words
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(i.e. tqlayout) is the one determined previously in tqlayout units. KoZoomHandler
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offers methods for converting between tqlayout units and zoom-dependent points
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and pixels.
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Note that the Internal coordinate system starts at the topleft corner of
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the first text frame, (whereas the other coordinate systems start at the
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topleft corner of the first page).
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Also, Internal coordinates only exists within the text frames.
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Internal coordinates can be converted to Document coordinates with
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KWTextFrameSet::internalToDocument(), and the other way round with documentToInternal().
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View:
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The same as the zoomed coordinate system, but this one can use multiple pages next to each
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other. So 3 pages horizontal in preview mode is no problem. A frame on page 3
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then has a higher X coordinate then the same frame on page 1 (and e.g. the same Y).
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When converting to Zoomed the X coordinates are equals, but the Y of the frame on page
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3 is higher than the Y of the frame on page 1.
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Document (pt values, in double, KoPoint, KoRect.)
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| |
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| |--KoZoomHander::zoomIt[XY] and unzoomIt[XY]
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| V
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| Zoomed coordinates (pixel values, in int, QPoint, QRect)
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| This is also called the "Normal" coordinate system.
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| |
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| |--KWViewMode::normalToView
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| V
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| View Mode (pixels values, but e.g. pages are re-arranged)
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| That's also the KWCanvas (scrollview)'s contents coordinates.
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| And for text framesets, there's also :
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|--KWTextFrameSet::documentToInternal
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V
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Internal coordinates (the coordinates given to QRT - in "tqlayout units")
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Note that there are pixels and pts in the tqlayout unit system too !
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There are conversions between LU points and document points,
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but also direct conversions between LU pixels and view pixels.
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Font sizes
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==========
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A 12pt font will lead to a tqlayout font of ptToLayoutUnit(12)=20*12=240pt -
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that's the value stored in the QTextFormat.
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However font metrics are calculated from the 100%-zoom-level font (e.g. 12pt for a 12pt font)
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and _then_ multiplied by 20, instead of loading a 240pt font for that as we did before.
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This is implemented by KoTextFormat::charWidth().
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On screen, at 100%, a tqlayoutUnitToFontSize(240,false)=(240/20)*1.0=20.0pt font size will be used.
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This does NOT depend on the DPI settings. Qt takes care of pt->pixel conversion for fonts.
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When printing... TODO, double-check whether Qt does pt->pixel conversion correctly
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(aptqparently it didn't, in Qt 2).
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QFont multiplies by 10 and stores into a 'short'... So for QFont the maximum font size
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is 3276, and in KOffice the maximum font size in points is around 163.
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See also
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========
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koffice/kword/DESIGN for more kword-specific things,
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and for explanation about KoTextView (text-edit objects)
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David Faure <faure@kde.org>
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