Function applyLumEffect

apps/sim/lib/pptx-renderer/renderer/image-renderer.ts:562–607

* Apply a luminance (brightness/contrast) effect to an image. * * OOXML ` ` supports `bright` (additive brightness offset, 0–100000 = 0–100%) * and `contrast` (multiplicative contrast, -100000 to 100000). * e.g. bright="100000" makes the entire image white (preserving alpha).

(lum: SafeXmlNode, img: HTMLImageElement)

 * e.g. bright="100000" makes the entire image white (preserving alpha).
 */
function applyLumEffect(lum: SafeXmlNode, img: HTMLImageElement): void {
  const bright = (lum.numAttr('bright') ?? 0) / 100000 // 0–1
  const contrast = (lum.numAttr('contrast') ?? 0) / 100000 // -1 to 1

  if (bright === 0 && contrast === 0) return

  const apply = () => {
    const w = img.naturalWidth
    const h = img.naturalHeight
    if (!w || !h) return

    const canvas = document.createElement('canvas')
    canvas.width = w
    canvas.height = h
    const c = canvas.getContext('2d')
    if (!c) return

    c.drawImage(img, 0, 0)
    const imageData = c.getImageData(0, 0, w, h)
    const data = imageData.data

    for (let i = 0; i < data.length; i += 4) {
      for (let ch = 0; ch < 3; ch++) {
        // Normalize to 0–1
        let v = data[i + ch] / 255
        // Apply contrast (expand/compress around 0.5)
        if (contrast !== 0) {
          v = 0.5 + (v - 0.5) * (1 + contrast)
        }
        // Apply additive brightness offset
        v += bright
        data[i + ch] = Math.round(Math.max(0, Math.min(255, v * 255)))
      }
      // Alpha preserved
    }

    c.putImageData(imageData, 0, 0)
    img.src = canvas.toDataURL()
  }

  if (img.complete && img.naturalWidth) {
    apply()
  } else {
    img.addEventListener('load', apply, { once: true })
  }
}

// ---------------------------------------------------------------------------
// BiLevel Effect