74 lines
2.1 KiB
Markdown
74 lines
2.1 KiB
Markdown
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SkRect
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======
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*Rectangles*
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<!--Updated Mar 4, 2011-->
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SkRect is basic to many drawing and measuring operations. It can be
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drawn using canvas.drawRect(), but it is also used to return the
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bounds of objects like paths and text characters. It is specified
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using SkScalar values.
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SkIRect is the integer counter part to SkRect, but is specified using
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32bit integers.
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<!--?prettify lang=cc?-->
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struct SkRect {
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SkScalar fLeft;
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SkScalar fTop;
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SkScalar fRight;
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SkScalar fBottom;
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// methods
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};
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SkRect rect = SkRect::MakeLTRB(left, top, right, bottom);
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SkRect has the usual getters, to return width(), height(), centerX(),
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etc. It also has methods to compute unions and intersections between
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rectangles.
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Converting between SkRect and SkIRect is asymetric. Short of overflow
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issues when SkScalar is an int, converting from SkIRect to SkRect is
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straight forward:
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<!--?prettify lang=cc?-->
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SkRect::set(const SkIRect&);
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However, convert from SkRect to SkIRect needs to know how to go from
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fractional values to integers.
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<!--?prettify lang=cc?-->
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SkRect::round(SkIRect*) const; // Round each coordinate.
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SkRect::roundOut(SkIRect*) const; // Apply floor to left/top,
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// and ceil to right/bottom.
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In Skia, rectangle coordinates describe the boundary of what is drawn,
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such that an empty rectangle encloses zero pixels:
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bool SkRect::isEmpty() const { return fLeft >= fRight || fTop >= fBottom; }
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<!--?prettify lang=cc?-->
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SkScalar SkRect::width() const { return fRight - fLeft; }
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SkScalar SkRect::height() const { return fBottom - fTop; }
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bool SkRect::contains(SkScalar x, SkScalar y) const {
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return fLeft <= x && x < fRight && fTop <= y && y < fBottom;
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}
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Thus, to draw a single pixel (assuming no matrix on the canvas), the
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rectangle should be initialized as follows:
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<!--?prettify lang=cc?-->
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SkRect r = SkRect::MakeXYWH(x, y, SkIntToScalar(1), SkIntToScalar(1));
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The same conventions hold for the integer counterpart: SkIRect. This
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also dovetails with SkRegion, which has the same model for set
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membership, and which uses SkIRect.
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