Macaw/Source/render/TextRenderer.swift

import Foundation
import UIKit

class TextRenderer: NodeRenderer {
	let text: Text

	init(text: Text, ctx: RenderContext, animationCache: AnimationCache) {
		self.text = text
		super.init(node: text, ctx: ctx, animationCache: animationCache)
	}

	override func node() -> Node {
		return text
	}

	override func doAddObservers() {
		super.doAddObservers()
		observe(text.textVar)
		observe(text.fontVar)
		observe(text.fillVar)
		observe(text.alignVar)
		observe(text.baselineVar)
	}

	override func doRender(_ force: Bool, opacity: Double) {
		let message = text.text
		let font = getUIFont()
		// positive NSBaselineOffsetAttributeName values don't work, couldn't find why
		// for now move the rect itself
		if var color = text.fill as? Color {
			color = RenderUtils.applyOpacity(color, opacity: opacity)
			UIGraphicsPushContext(ctx.cgContext!)
            message.draw(in: getBounds(font), withAttributes: [NSFontAttributeName: font,
                NSForegroundColorAttributeName: getTextColor(color)])
			UIGraphicsPopContext()
		}
	}

    fileprivate func getUIFont() -> UIFont {
        if let textFont = text.font {
            if let customFont = UIFont(name: textFont.name, size: CGFloat(textFont.size)) {
                return customFont
            } else {
                return UIFont.systemFont(ofSize: CGFloat(textFont.size))
            }
        }
        return UIFont.systemFont(ofSize: UIFont.systemFontSize)
    }

    fileprivate func getBounds(_ font: UIFont) -> CGRect {
        let textAttributes = [NSFontAttributeName: font]
        let textSize = NSString(string: text.text).size(attributes: textAttributes)
        return CGRect(x: calculateAlignmentOffset(text, font: font),
                          y: calculateBaselineOffset(text, font: font),
                          width: CGFloat(textSize.width), height: CGFloat(textSize.height))
    }

	fileprivate func calculateBaselineOffset(_ text: Text, font: UIFont) -> CGFloat {
		var baselineOffset = CGFloat(0)
		switch text.baseline {
		case Baseline.alphabetic:
			baselineOffset = font.ascender
		case Baseline.bottom:
			baselineOffset = font.ascender - font.descender
		case Baseline.mid:
			baselineOffset = (font.ascender - font.descender) / 2
		default:
			break
		}
		return -baselineOffset
	}

	fileprivate func calculateAlignmentOffset(_ text: Text, font: UIFont) -> CGFloat {
		let textAttributes = [
			NSFontAttributeName: font
		]
		let textSize = NSString(string: text.text).size(attributes: textAttributes)
		var alignmentOffset = CGFloat(0)
		switch text.align {
		case Align.mid:
			alignmentOffset = textSize.width / 2
		case Align.max:
			alignmentOffset = textSize.width
		default:
			break
		}
		return -alignmentOffset
	}

	fileprivate func getTextColor(_ fill: Fill) -> UIColor {
		if let color = fill as? Color {
			return UIColor(cgColor: RenderUtils.mapColor(color))
		}
		return UIColor.black
	}
}