TextMetrics & rendered text changed from v1.0.2 to v^2.0.0

[MarosPistej]

About

Texts aren't rendered same as in v1.0.2, TextMetrics are different for all textBaseLine but it is most noticeable for top && bottom, when middle || alphabetic are used changes are very small.

baseline: alphabetic
baseline: bottom

old: v1.0.2, new: v2.0.1

Notice: how text is shifted upwards when baseline: bottom

Reproducible example

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function drawTestText() {
  const width = 150
  const height = 100
  const canvas = new Canvas(width, height)
  const context = canvas.getContext('2d')

  context.fillStyle = 'white'
  context.fillRect(0, 0, width, height)

  context.strokeStyle = 'blue'
  context.beginPath()
  for (let i = 0; i < height; i += 10) {
    context.moveTo(0, i)
    context.lineTo(width, i)
  }
  context.stroke()
  context.closePath()

  context.font = '50px Lato'
  context.fillStyle = 'black'
  context.textAlign = 'left'
  context.textBaseline = 'bottom'
  const text = 'TEST'
  const measurements = context.measureText(text)
  console.log(measurements)
  context.fillText(text, 25, 75)

  context.beginPath()
  context.strokeStyle = 'red'
  context.strokeRect(
    25 + measurements.lines[0].x,
    75 + measurements.lines[0].y,
    measurements.lines[0].width,
    measurements.lines[0].height
  )
}

Expected behavior

I am unsure about this, to be honest. This is causing me problems because I had fine-tuned my render functions to display text in specific positions based on TextMetrics. Primarily, I would like to know if this is/was an expected change between versions and, if possible, what caused it.

[samizdatco]

Nothing changed between v1 and v2 within skia-canvas itself, but it upgrades to a much newer revision of rust-skia, so things have almost certainly changed under the hood. However: one alternative explanation that comes to mind is that your system is now using gpu-based rendering as of v2 (in which case setting canvas.gpu = false would yield different results).

That said, after looking over the way different baselines are computed (for #209) I think I've found some modifications that would better match the way browsers calculate offsets and determine the default leading when a lineHeight value isn't included in the ctx.font assignment.

More to come…