Embedded raster images in pdf plotting output

[vvolkl]

Feature description

I was making this nice VIOLIN6 in ROOT:

But the icons I added don't show up in the pdf I tried to save from the script:

violin_bundle.pdf

with the script telling me:

   Warning in <TASImage::Paint>: PDF not implemented yet

I ended up postprocessing the pdf, which is a minor annoyance (also I hit a few more ROOT quirks while doing it). It'd be nice to implement drawing bitmaps to pdf too. I have an (untested, unreviewed) AI-generated patch here: https://github.com/vvolkl/root/tree/tasimage-draw-pdf

I'm happy prepare a proper PR from that branch if that's OK from the maintainer side.

Previous discussions:

https://root-forum.cern.ch/t/tasimage-not-implemented-for-pdf/10476
https://root-forum.cern.ch/t/warning-in-tasimage-paint-pdf-not-implemeted-yet/20122

Minimal reproducer

// Minimal ROOT repro for TASImage PDF output.
// Run:
//   root -l -b -q minimal_tasimage_pdf_warning.C

void minimal_tasimage_pdf_warning() {
    gROOT->SetBatch(kTRUE);

    // Create a tiny PNG asset using ROOT itself so the repro is self-contained.
    auto *src = new TCanvas("src", "src", 64, 64);
    auto *box = new TBox(0.15, 0.15, 0.85, 0.85);
    box->SetFillColor(kRed + 1);
    box->SetLineColor(kRed + 2);
    box->Draw();
    src->SaveAs("minimal_icon.png");

    // Re-open the PNG through TImage/TASImage and draw it on a second canvas.
    auto *c = new TCanvas("c", "c", 400, 300);
    auto *img = TImage::Open("minimal_icon.png");
    if (!img) {
        Error("minimal_tasimage_pdf_warning", "could not open minimal_icon.png");
        return;
    }

    auto *pad = new TPad("imgpad", "", 0.35, 0.25, 0.65, 0.75);
    pad->SetFillStyle(4000);
    pad->SetFrameFillStyle(0);
    pad->SetBorderMode(0);
    pad->SetBorderSize(0);
    pad->SetTopMargin(0);
    pad->SetBottomMargin(0);
    pad->SetLeftMargin(0);
    pad->SetRightMargin(0);
    pad->Draw();
    pad->cd();
    img->Draw("X");
    c->cd();

    c->SaveAs("minimal_tasimage_pdf_warning.pdf"); // empty
    c->SaveAs("minimal_tasimage_pdf_warning.png"); // shows box
}

ROOT version:

root --version
ROOT Version: 6.38.04
Built for macosxarm64 on Mar 11 2026, 21:39:24
From tags/6-38-04@6-38-04

Alternatives considered

No response

Additional context

No response

[linev]

Please create PR with your changes.

[vvolkl]

Please create PR with your changes.

Done; I've read up on the pdf format and done one more iteration using an image XObject instead of the inline graphics in the original branch. Bit more complex, but seems like the better way to do it.