diff --git a/components/gfx/paint_context.rs b/components/gfx/paint_context.rs index 62ac45bab79..ab258e2ef6e 100644 --- a/components/gfx/paint_context.rs +++ b/components/gfx/paint_context.rs @@ -484,7 +484,81 @@ impl<'a> PaintContext<'a> { radius.width <= 0. || radius.height <= 0. } - // Adapted from gecko:gfx/2d/PathHelpers.h:EllipseToBezier + // The following comment is wonderful, and stolen from + // gecko:gfx/thebes/gfxContext.cpp:RoundedRectangle for reference. + // --------------------------------------------------------------- + // + // For CW drawing, this looks like: + // + // ...******0** 1 C + // **** + // *** 2 + // ** + // * + // * + // 3 + // * + // * + // + // Where 0, 1, 2, 3 are the control points of the Bezier curve for + // the corner, and C is the actual corner point. + // + // At the start of the loop, the current point is assumed to be + // the point adjacent to the top left corner on the top + // horizontal. Note that corner indices start at the top left and + // continue clockwise, whereas in our loop i = 0 refers to the top + // right corner. + // + // When going CCW, the control points are swapped, and the first + // corner that's drawn is the top left (along with the top segment). + // + // There is considerable latitude in how one chooses the four + // control points for a Bezier curve approximation to an ellipse. + // For the overall path to be continuous and show no corner at the + // endpoints of the arc, points 0 and 3 must be at the ends of the + // straight segments of the rectangle; points 0, 1, and C must be + // collinear; and points 3, 2, and C must also be collinear. This + // leaves only two free parameters: the ratio of the line segments + // 01 and 0C, and the ratio of the line segments 32 and 3C. See + // the following papers for extensive discussion of how to choose + // these ratios: + // + // Dokken, Tor, et al. "Good approximation of circles by + // curvature-continuous Bezier curves." Computer-Aided + // Geometric Design 7(1990) 33--41. + // Goldapp, Michael. "Approximation of circular arcs by cubic + // polynomials." Computer-Aided Geometric Design 8(1991) 227--238. + // Maisonobe, Luc. "Drawing an elliptical arc using polylines, + // quadratic, or cubic Bezier curves." + // http://www.spaceroots.org/documents/ellipse/elliptical-arc.pdf + // + // We follow the approach in section 2 of Goldapp (least-error, + // Hermite-type approximation) and make both ratios equal to + // + // 2 2 + n - sqrt(2n + 28) + // alpha = - * --------------------- + // 3 n - 4 + // + // where n = 3( cbrt(sqrt(2)+1) - cbrt(sqrt(2)-1) ). + // + // This is the result of Goldapp's equation (10b) when the angle + // swept out by the arc is pi/2, and the parameter "a-bar" is the + // expression given immediately below equation (21). + // + // Using this value, the maximum radial error for a circle, as a + // fraction of the radius, is on the order of 0.2 x 10^-3. + // Neither Dokken nor Goldapp discusses error for a general + // ellipse; Maisonobe does, but his choice of control points + // follows different constraints, and Goldapp's expression for + // 'alpha' gives much smaller radial error, even for very flat + // ellipses, than Maisonobe's equivalent. + // + // For the various corners and for each axis, the sign of this + // constant changes, or it might be 0 -- it's multiplied by the + // appropriate multiplier from the list before using. + // --------------------------------------------------------------- + // + // Code adapted from gecko:gfx/2d/PathHelpers.h:EllipseToBezier fn ellipse_to_bezier(path_builder: &mut PathBuilder, origin: Point2D, radius: Size2D, @@ -629,86 +703,6 @@ impl<'a> PaintContext<'a> { } } - // The following comment is wonderful, and stolen from - // gecko:gfx/thebes/gfxContext.cpp:RoundedRectangle for reference. - // - // It does not currently apply to the code, but will be extremely useful in - // the future when the below TODO is addressed. - // - // TODO(cgaebel): Switch from arcs to beziers for drawing the corners. - // Then, add http://www.subcide.com/experiments/fail-whale/ - // to the reftest suite. - // - // --------------------------------------------------------------- - // - // For CW drawing, this looks like: - // - // ...******0** 1 C - // **** - // *** 2 - // ** - // * - // * - // 3 - // * - // * - // - // Where 0, 1, 2, 3 are the control points of the Bezier curve for - // the corner, and C is the actual corner point. - // - // At the start of the loop, the current point is assumed to be - // the point adjacent to the top left corner on the top - // horizontal. Note that corner indices start at the top left and - // continue clockwise, whereas in our loop i = 0 refers to the top - // right corner. - // - // When going CCW, the control points are swapped, and the first - // corner that's drawn is the top left (along with the top segment). - // - // There is considerable latitude in how one chooses the four - // control points for a Bezier curve approximation to an ellipse. - // For the overall path to be continuous and show no corner at the - // endpoints of the arc, points 0 and 3 must be at the ends of the - // straight segments of the rectangle; points 0, 1, and C must be - // collinear; and points 3, 2, and C must also be collinear. This - // leaves only two free parameters: the ratio of the line segments - // 01 and 0C, and the ratio of the line segments 32 and 3C. See - // the following papers for extensive discussion of how to choose - // these ratios: - // - // Dokken, Tor, et al. "Good approximation of circles by - // curvature-continuous Bezier curves." Computer-Aided - // Geometric Design 7(1990) 33--41. - // Goldapp, Michael. "Approximation of circular arcs by cubic - // polynomials." Computer-Aided Geometric Design 8(1991) 227--238. - // Maisonobe, Luc. "Drawing an elliptical arc using polylines, - // quadratic, or cubic Bezier curves." - // http://www.spaceroots.org/documents/ellipse/elliptical-arc.pdf - // - // We follow the approach in section 2 of Goldapp (least-error, - // Hermite-type approximation) and make both ratios equal to - // - // 2 2 + n - sqrt(2n + 28) - // alpha = - * --------------------- - // 3 n - 4 - // - // where n = 3( cbrt(sqrt(2)+1) - cbrt(sqrt(2)-1) ). - // - // This is the result of Goldapp's equation (10b) when the angle - // swept out by the arc is pi/2, and the parameter "a-bar" is the - // expression given immediately below equation (21). - // - // Using this value, the maximum radial error for a circle, as a - // fraction of the radius, is on the order of 0.2 x 10^-3. - // Neither Dokken nor Goldapp discusses error for a general - // ellipse; Maisonobe does, but his choice of control points - // follows different constraints, and Goldapp's expression for - // 'alpha' gives much smaller radial error, even for very flat - // ellipses, than Maisonobe's equivalent. - // - // For the various corners and for each axis, the sign of this - // constant changes, or it might be 0 -- it's multiplied by the - // appropriate multiplier from the list before using. #[allow(non_snake_case)] fn create_border_path_segment(&self, path_builder: &mut PathBuilder, diff --git a/tests/html/border_twitter_fail_whale.html b/tests/html/border_twitter_fail_whale.html new file mode 100644 index 00000000000..c34a836427e --- /dev/null +++ b/tests/html/border_twitter_fail_whale.html @@ -0,0 +1,1355 @@ + + + + + Pure CSS Twitter Fail Whale - By Steve Dennis (http://www.subcide.com/experiments/fail-whale/) + + + + +

Pure CSS Twitter 'Fail Whale' by Steve Dennis (http://www.subcide.com/experiments/fail-whale/).

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