kitepdf-core/io.github.yuroyami.kitepdf.core.render/KiteCanvas

KiteCanvas

High-level drawing target. Implement this to add a new render backend; use PdfPage.renderTo to drive an existing one.

The PageRenderer walks the content stream, maintains the graphics-state stack, accumulates paths, and finally calls one of these device methods with a complete, ready-to-paint primitive. Backends therefore don't need to track the CTM, the current path, or text positioning. They receive only the final geometry plus the transform to apply.

Concrete implementations shipped:

ComposeCanvas (:kitepdf-compose-viewer): paints into a Compose DrawScope.
SkiaCanvas (:kitepdf-skia-renderer): paints into a Skia Canvas.
AwtCanvas / AndroidNativeCanvas / CoreGraphicsCanvas / Canvas2dCanvas (:kitepdf-native-renderer): host-platform raster backends.

Inheritors

NoopCanvas

RecordingCanvas

Properties

resolvesGlyphOutlines

open val resolvesGlyphOutlines: Boolean

True when this canvas needs resolved glyph outlines (TextGlyph.outline), i.e. it actually paints (a render backend). Extraction canvases that only read text + advances override this to false, letting the driver skip the cost of resolving glyph outlines. Such a canvas gets every text run through drawGlyphs, also a run that paints nothing, such as invisible OCR text.

Functions

applySoftMask

open fun applySoftMask(kind: SoftMask.Kind, maskBBox: KiteRectangle, maskCtm: KiteMatrix, render: () -> Unit, renderMask: (KiteCanvas) -> Unit)

Apply a soft mask to the content rendered inside render (ISO 32000-1 §11.6.5). The default implementation just calls render. Backends without offscreen compositing fall back to painting through the mask.

open fun applySoftMask(kind: SoftMask.Kind, maskBBox: KiteRectangle, maskCtm: KiteMatrix, transfer: KiteMaskTransfer?, render: () -> Unit, renderMask: (KiteCanvas) -> Unit)

Applies a soft mask whose values pass through transfer before they gate the content (ISO 32000-1, 11.6.5.2, Table 144, /TR). A null transfer is the identity. The transfer applies to every mask value, also where the group paints nothing.

beginPage

abstract fun beginPage(widthPt: Double, heightPt: Double, deviceCtm: KiteMatrix)

Set up for a page render. The renderer calls this once before any draw call, with the page dimensions (in PDF user units, 1pt = 1/72 inch) and the desired device CTM (e.g. flip Y and scale to fit a target rectangle).

beginTransparencyGroup

open fun beginTransparencyGroup(bbox: KiteRectangle, ctm: KiteMatrix, isolated: Boolean = false, knockout: Boolean = false, alpha: Double = 1.0, blendMode: KiteBlendMode = KiteBlendMode.Normal)

Open a transparency group (ISO 32000-1 §11.4). Subsequent paints accumulate into an offscreen layer; endTransparencyGroup composites the layer back onto the parent with blendMode + alpha.

drawGlyphs

abstract fun drawGlyphs(glyphs: List<TextGlyph>, fontSize: Double, unitsPerEm: Int, hasOutlines: Boolean, fontSpec: FontSpec, textToDevice: KiteMatrix, color: RgbColor, alpha: Double = 1.0, blendMode: KiteBlendMode = KiteBlendMode.Normal)

Paint one text run, already laid out into glyphs by the document handler. Format-neutral: no PDF (or other) font object crosses the seam, so every handler (PDF, EPUB, and others) drives text the same way.

drawImage

open fun drawImage(image: KiteImageData, ctm: KiteMatrix, alpha: Double = 1.0)

Paint an XObject Image under ctm. PDF defines the image's bounds as the unit square (0..1, 0..1); the CTM already encodes the scale + position. Backends that can decode image paint the pixels; others draw a placeholder rather than throw.

open fun drawImage(image: KiteImageData, ctm: KiteMatrix, alpha: Double, blendMode: KiteBlendMode)

Paint an XObject Image as drawImage does, composited with blendMode. The blend mode of the graphics state applies to an image as to every other paint (ISO 32000-1, 11.3.5).

endPage

abstract fun endPage()

endTransparencyGroup

open fun endTransparencyGroup()

fillPath

abstract fun fillPath(path: KitePath, ctm: KiteMatrix, color: RgbColor, evenOdd: Boolean, alpha: Double = 1.0, blendMode: KiteBlendMode = KiteBlendMode.Normal)

Fill path under ctm with color at alpha (0..1) under the given blendMode. The default alpha = 1.0 + blendMode = Normal is the plain over-paint that PDF assumes when no ExtGState modifies the state.

fillShading

open fun fillShading(shading: KiteShading, ctm: KiteMatrix, clipPath: KitePath?, alpha: Double = 1.0, blendMode: KiteBlendMode = KiteBlendMode.Normal)

Fill clipPath (under ctm) with the gradient defined by shading. If clipPath is null the shading covers the current clip region (or the page, when no clip is active). That is the spec's sh operator.

hostGlyphOutline

open fun hostGlyphOutline(text: String, fontSpec: FontSpec): KitePath?

The outline of text in the host face this canvas draws a font without embedded outlines in, chosen from fontSpec as drawGlyphs chooses it. The outline is in glyph space: 1000 units per em, y up, and the pen at the origin on the baseline. A document handler strokes and clips such text with it, since a missing font program does not excuse the stroke (ISO 32000-1, 9.3.6).

paintComplexShading

fun KiteCanvas.paintComplexShading(shading: KiteShading, ctm: KiteMatrix, clipPath: KitePath?, alpha: Double = 1.0, blendMode: KiteBlendMode = KiteBlendMode.Normal): Boolean

Renders the complex shading types, so every backend supports them identically with no code of its own:

popClip

abstract fun popClip()

pushClip

abstract fun pushClip(path: KitePath, ctm: KiteMatrix, evenOdd: Boolean)

Push a clip to path under ctm. Matched 1:1 by popClip.

strokePath

abstract fun strokePath(path: KitePath, ctm: KiteMatrix, color: RgbColor, lineWidth: Double, alpha: Double = 1.0, blendMode: KiteBlendMode = KiteBlendMode.Normal, dashArray: List<Double>? = null, dashPhase: Double = 0.0, lineCap: Int = 0, lineJoin: Int = 0, miterLimit: Double = 10.0)

Stroke path under ctm with color at lineWidth user-units, alpha, blendMode. lineCap 0/1/2 = butt/round/square; lineJoin 0/1/2 = miter/round/bevel.