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absolute-placement.md

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Absolute placement (canvas)

When you need pixel-precise control — a certificate, a badge, a diploma, a poster — reach for a canvas layer. addCanvas(width, height, canvas -> ...) reserves a fixed-size rectangle in the surrounding flow and lets you drop children at explicit (x, y) coordinates inside it.

(0, 0) is the canvas's top-left corner; positive x extends right and positive y extends down (the screen convention). The canvas occupies its declared width x height in the flow no matter where its children land.

A positioned certificate block

import com.demcha.compose.document.dsl.ParagraphBuilder;
import com.demcha.compose.document.node.TextAlign;
import com.demcha.compose.document.style.ClipPolicy;

document.pageFlow()
        .addCanvas(523, 300, canvas -> canvas
                .name("Certificate")
                .clipPolicy(ClipPolicy.CLIP_BOUNDS)
                .position(new ParagraphBuilder()
                        .text("CERTIFICATE OF ACHIEVEMENT")
                        .textStyle(eyebrow)
                        .align(TextAlign.CENTER)
                        .build(), 0, 40)
                .position(new ParagraphBuilder()
                        .text("Jordan Rivera")
                        .textStyle(name)
                        .align(TextAlign.CENTER)
                        .build(), 0, 90))
        .build();

A child placed at x = 0 is prepared with the full canvas width, so TextAlign.CENTER centres it across the whole canvas. A child placed at x > 0 inherits that same prepared width — give such a paragraph a horizontal margin if it must not overflow the right edge.

Clipping

clipPolicy(ClipPolicy.CLIP_BOUNDS) hides anything that overflows the canvas rectangle. The default leaves overflow visible — useful for a decorative element that intentionally bleeds past the box.

Canvas vs. the flow

The canvas does not flow or wrap its children — they sit exactly where you place them. Everything outside the canvas (the surrounding pageFlow()) still flows and paginates normally; the canvas is one fixed block within it. Because the box is fixed, a canvas does not split across a page break — keep its height within one page.

See also