Bezier

This is an implementation of cubic and quadratic Bezier curves for Gideros. Features:

• Is a Gideros "Shape" object for easy integration into your project.
• Very quick calculation of cubic and quadratic Bezier curves.
• Automatic scaling of number of steps.
• Deferred drawing (the most expensive operation) until you want it.
• Optional reduction of calculated points to just those needed. Can generally result in a reduction of 25% to 75% depending on the curve.
• Length of curve calculation.

#Install

Just add the Bezier.lua file to your project.

Example

local curve = Bezier.new()
stage:addChild(curve)

local p1 = {x=50,y=50}
local p2 = {x=200,y=50}
local p3 = {x=50,y=200}
local p4 = {x=200,y=200}

curve:createCubicCurve(p1, p2, p3, p4)
curve:reduce()
curve:setLineStyle(2, 0x000000, 1)
curve:setFillStyle(Shape.SOLID, 0xFF0000, 1)
curve:draw(true) -- Draw as a closed path

Notes

It is important to remember that this class is based on the Gideros Shape class. Therefore, you need to set a line and/or fill style before calling Bezier:draw() as the default for a Shape object is to be invisible. Also, if you want to call draw() again after calculating new points, you need to call clear() then set the line and fill styles again. Think of this class as a Shape that adds functions to replace the actual calls to beginPath(), moveTo(), lineTo(), closePath() and endPath(). Otherwise, everything else is true.

#Methods

###Bezier.new() Creates a new Bezier object, which inherits from Shape.

###Bezier:getPoints() Returns a table/list of points, if any have been calculated.

###Bezier:setPoints(points) Sets the points used to draw the curve.

Parameters:

• points - A table/list of points in the format {{x=0,y=0}, ...}

###Bezier:setAutoStepScale(scale) Sets the factor used to estimate the number of steps to use if none are explicitly given. The formula is:

d1 = distance between p1 and p2
d2 = distance between p2 and p3
d3 = distance between p3 and p4

steps = (d1 + d2 + d3) * scale

Parameters:

• scale - Basically the percentage of the distance between the start, end and control points of a curve. Default: .1

###Bezier:getAutoStepScale() Returns the current auto step scale factor.

###Bezier:getLength() Returns the total length of the curve by adding up the distance between each point in the curve.

###Bezier:draw(isClosed) Draws the curve using the inherited Shape methods as a series of lines. Remember, you have to add the curve somewhere in the scene graph for it to be visible.

Parameters:

• isClosed - Controls whether the curve is drawn as a closed path or not. Default: false

###Bezier:createQuadraticCurve(p1, p2, p3, steps) Calculates the points needed to form a quadratic curve comprised of a start point (p1), a single control point (p2) and an end point (p3).

Parameters:

• p1: Beginning of the path. Must be table with 'x' and 'y' keys, i.e. {x=100,y=100}
• p2: First control point of the path. Must be table with 'x' and 'y' keys, i.e. {x=100,y=100}
• p3: End of the path. Must be table with 'x' and 'y' keys, i.e. {x=100,y=100}
• steps: Number of steps to create in the path. Default: estimate based on distance between points. See Bezier:setAutoStepScale

###Bezier:createCubicCurve(p1, p2, p3, p4, steps) Calculates the points needed to form a cubic curve comprised of a start point (p1), a control point (p2), another control point (p3) and an end point (p4).

Parameters:

• p1: Beginning of the path. Must be table with 'x' and 'y' keys, i.e. {x=100,y=100}
• p2: First control point of the path. Must be table with 'x' and 'y' keys, i.e. {x=100,y=100}
• p3: Second control point of the path. Must be table with 'x' and 'y' keys, i.e. {x=100,y=100}
• p4: End of the path. Must be table with 'x' and 'y' keys, i.e. {x=100,y=100}
• steps: Number of steps to create in the path. Default: estimate based on distance between points. See Bezier:setAutoStepScale

###Bezier:reduce(epsilon) Reduces the number of points in the path by examining the distance between each point and line from surrounding points. If the point is greater than epsilon then it will be kept, otherwise it is discarded.

Parameters:

• epsilon: Minimum distance from the line of the curve for a point to be kept. Higher values result in more points being thrown away. Default: .1