This is the core PDF viewer code:

@Stable
class PDFContext(pdf: String) {
    val pdfFile = File(pdf)
    val document = Loader.loadPDF(pdfFile)
    val pdfRenderer = PDFRenderer(document)
}

@Composable
fun DocumentView(pdfContext: PDFContext, pageIndex: Int, modifier: Modifier = Modifier) {
    Box(modifier.fillMaxSize().drawWithCache {
        onDrawBehind {
            drawIntoCanvas {
                val w = size.width
                val h = size.height
                clipRect(0f, 0f, w, h){
                    with (it.nativeCanvas) {
                        SkikoGraphics2D(this).also { g2 ->
                            g2.background = java.awt.Color.LIGHT_GRAY
                            g2.clearRect(0, 0, w.toInt(), h.toInt())
                            with(pdfContext) {
                                val page = document.getPage(pageIndex)
                                val cb = page.cropBox
                                val scale = min(w/cb.width, h/cb.height)
                                val sx = cb.lowerLeftX*scale
                                val sy = cb.lowerLeftY*scale
                                val sw = cb.width*scale
                                val sh = cb.height*scale
                                if (sw <= w) g2.translate(0.5 * (w - sw), 0.0) // center horizontally on canvas.
                                if (sh <= h) g2.translate(0.0, 0.5 * (h - sh)) // center vertically on canvas.
                                g2.background = java.awt.Color.WHITE
                                g2.clearRect(sx.toInt(), sy.toInt(), sw.toInt(), sh.toInt())
                                pdfRenderer.renderPageToGraphics(pageIndex, g2, scale)
                                log.debug { "pdfRenderer.renderPageToGraphics" }
                            }
                        }
                    }
                }
            }
        }
    })
}

At the moment I see two main problems: 1. When I just move the mouse (no buttons pressed) over the buttons at the top of the app or over the document area then I can see that the graphics seems to be constantly re-rendered. I thought that exactly this should not happen when I use the drawWithCache modifier and even without it I would not expect that. 2. During the procedure above I see lots of strange rendering artefakts popping up which mostly disappear as soon as I leave the mouse untouched but not always. Somehow it looks like there might be concurrency problems but can that be with this setup? I have to admit that I am a bit lost here and don’t know where to look. Is there any documentation on how one should deal with heavy rendering jobs like this in compose to get the best performance?