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Fixes #4099: Line renderer did not render lines if their coordinates fell outside of the viewport. #4100

Merged
merged 7 commits into from
Oct 9, 2019
23 changes: 13 additions & 10 deletions Source/Charts/Renderers/LineChartRenderer.swift
Original file line number Diff line number Diff line change
Expand Up @@ -354,17 +354,20 @@ open class LineChartRenderer: LineRadarRenderer
_lineSegments[i] = _lineSegments[i].applying(valueToPixelMatrix)
}

if (!viewPortHandler.isInBoundsRight(_lineSegments[0].x))
{
break
}
// Determine the start and end coordinates of the line, and make sure they differ.
guard
let firstCoordinate = _lineSegments.first,
let lastCoordinate = _lineSegments.last,
firstCoordinate != lastCoordinate else { continue }

// make sure the lines don't do shitty things outside bounds
if !viewPortHandler.isInBoundsLeft(_lineSegments[1].x)
|| (!viewPortHandler.isInBoundsTop(_lineSegments[0].y) && !viewPortHandler.isInBoundsBottom(_lineSegments[1].y))
{
continue
}
// If both points lie left of viewport, skip stroking.
if !viewPortHandler.isInBoundsLeft(lastCoordinate.x) { continue }

// If both points lie right of the viewport, break out early.
if !viewPortHandler.isInBoundsRight(firstCoordinate.x) { break }

// Only stroke the line if it intersects with the viewport.
guard viewPortHandler.isIntersectingLine(from: firstCoordinate, to: lastCoordinate) else { continue }

// get the color that is set for this line-segment
context.setStrokeColor(dataSet.color(atIndex: j).cgColor)
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57 changes: 57 additions & 0 deletions Source/Charts/Utils/ViewPortHandler.swift
Original file line number Diff line number Diff line change
Expand Up @@ -416,6 +416,17 @@ open class ViewPortHandler: NSObject
return isInBoundsTop(y) && isInBoundsBottom(y)
}

/**
A method to check whether coordinate lies within the viewport.

- Parameters:
- point: a coordinate.
*/
@objc open func isInBounds(point: CGPoint) -> Bool
{
return isInBounds(x: point.x, y: point.y)
}

@objc open func isInBounds(x: CGFloat, y: CGFloat) -> Bool
{
return isInBoundsX(x) && isInBoundsY(y)
Expand Down Expand Up @@ -443,6 +454,52 @@ open class ViewPortHandler: NSObject
return (_contentRect.origin.y + _contentRect.size.height) >= normalizedY
}

/**
A method to check whether a line between two coordinates intersects with the view port by using a linear function.

Linear function (calculus): `y = ax + b`

Note: this method will not check for collision with the right edge of the view port, as we assume lines run from left
to right (e.g. `startPoint < endPoint`).

- Parameters:
- startPoint: the start coordinate of the line.
- endPoint: the end coordinate of the line.
*/
@objc open func isIntersectingLine(from startPoint: CGPoint, to endPoint: CGPoint) -> Bool
{
// If start- and/or endpoint fall within the viewport, bail out early.
if isInBounds(point: startPoint) || isInBounds(point: endPoint) { return true }
// check if x in bound when it's a vertical line
if startPoint.x == endPoint.x { return isInBoundsX(startPoint.x) }

// Calculate the slope (`a`) of the line (e.g. `a = (y2 - y1) / (x2 - x1)`).
let a = (endPoint.y - startPoint.y) / (endPoint.x - startPoint.x)
// Calculate the y-correction (`b`) of the line (e.g. `b = y1 - (a * x1)`).
let b = startPoint.y - (a * startPoint.x)

// Check for colission with the left edge of the view port (e.g. `y = (a * minX) + b`).
// if a is 0, it's a horizontal line; checking b here is still valid, as b is `point.y` all the time
if isInBoundsY((a * contentRect.minX) + b) { return true }

// Skip unnecessary check for collision with the right edge of the view port
// (e.g. `y = (a * maxX) + b`), as such a line will either begin inside the view port,
// or intersect the left, top or bottom edges of the view port. Leaving this logic here for clarity's sake:
// if isInBoundsY((a * contentRect.maxX) + b) { return true }

// While slope `a` can theoretically never be `0`, we should protect against division by zero.
guard a != 0 else { return false }

// Check for collision with the bottom edge of the view port (e.g. `x = (maxY - b) / a`).
if isInBoundsX((contentRect.maxY - b) / a) { return true }

// Check for collision with the top edge of the view port (e.g. `x = (minY - b) / a`).
if isInBoundsX((contentRect.minY - b) / a) { return true }

// This line does not intersect the view port.
return false
}

/// The current x-scale factor
@objc open var scaleX: CGFloat
{
Expand Down