pdf

PDF Package

The pdf package provides Leadtype's low-level PDF drawing API: document and page writers, text and image output, path drawing, font registration, and related serialization support.

Tagged PDF Accessibility

Tagged PDF output is off by default. Enable it explicitly when you want the writer to emit PDF structure trees, marked-content identifiers, and related accessibility objects:

doc := pdf.NewDocWriter()
doc.EnableTaggedPDF(true)

Leadtype writes PDF 1.7 documents and emits /StructTreeRoot, /MarkInfo, /ParentTree, page /StructParents, and marked-content associations when tagged output is enabled.

Use semantic scopes to associate rendered output with structure elements:

err := doc.WithAccessibilityTag("P", pdf.AccessibilityOptions{
	ActualText: "Accessible greeting",
}, func() {
	doc.MoveTo(1, 1)
	_ = doc.Print("Hello")
})
if err != nil {
	panic(err)
}

Use artifact scopes for decorative or non-reading-order output:

err := doc.WithAccessibilityArtifact(func() {
	doc.Rectangle(0.5, 0.5, 7.5, 10, true, false)
})
if err != nil {
	panic(err)
}

The same APIs are available on PageWriter. LTML uses this writer-level support under the hood when a document opts into ua="true".

In LTML, /ActualText is applied conservatively at higher-level structure elements such as paragraphs, labels, and opted-in graphics. Fine-grained copy/paste still relies on ToUnicode mappings rather than inline /ActualText overrides.

Gradients

Leadtype supports linear (axial) and radial gradients for PDF drawing.

Use SetFillLinearGradient or SetFillRadialGradient to make a gradient the active fill color for subsequent shapes:

if err := doc.SetFillLinearGradient(&pdf.LinearGradient{
	X0: 1, Y0: 1, X1: 4, Y1: 1,
	Stops: []pdf.GradientStop{
		{Position: 0, Color: colors.Red},
		{Position: 1, Color: colors.Blue},
	},
}); err != nil {
	panic(err)
}
doc.Rectangle(1, 1, 3, 1.5, false, true)

Use SetLineLinearGradient or SetLineRadialGradient for stroked outlines, and call ClearFillGradient or ClearLineGradient to return to solid colors.

Gradient stops must:

• start at 0
• end at 1
• increase strictly between stops

Gradient coordinates use the current document unit system, just like other drawing operations.

Painting Into A Clip

Use PaintLinearGradient or PaintRadialGradient when you want to paint a shading directly into the current clipping region instead of using it as the current fill or stroke color:

if err := doc.Path(func() {
	doc.MoveTo(5, 5)
	doc.LineTo(7, 5)
	doc.LineTo(7, 7)
	doc.LineTo(5, 7)
	doc.LineTo(5, 5)
	_ = doc.Clip(func() {
		_ = doc.PaintLinearGradient(&pdf.LinearGradient{
			X0: 5, Y0: 5, X1: 7, Y1: 7,
			Stops: []pdf.GradientStop{
				{Position: 0, Color: colors.White},
				{Position: 1, Color: colors.DarkBlue},
			},
		})
	})
}); err != nil {
	panic(err)
}

Use fill/stroke gradients when the gradient should behave like the current drawing color for later path operations. Use Paint*Gradient when the gradient should fill the current clip immediately.

Pseudo-Sweep Bands

Leadtype also supports sweep-like annular bands built from explicit angular segments and clipped linear paints.

Use PaintSweepBand when you want to compose a ring from solid wedges and gradient wedges without introducing a new PDF shading type:

err := doc.PaintSweepBand(&pdf.SweepBand{
	X: 6.25, Y: 8.5,
	InnerRadius: 0.58,
	OuterRadius: 1.02,
	Segments: []pdf.SweepBandSegment{
		{StartAngle: -22.5, EndAngle: 22.5, StartColor: colors.Red, EndColor: colors.Red},
		{StartAngle: 22.5, EndAngle: 67.5, StartColor: colors.Red, EndColor: colors.Yellow, Steps: 12},
	},
})
if err != nil {
	panic(err)
}

Each segment is clipped to its annular slice. Gradient segments use a linear gradient whose axis follows the chord between the segment's start-angle and end-angle points at the midpoint radius, which gives horizontal, vertical, or diagonal blends depending on the slice. If StartColor and EndColor are the same, the segment renders as a visually solid band while still using the same gradient paint path.

Set Steps on a segment to subdivide it into that many equal-angle painted subsegments. This makes it practical to approximate the older “many thin arches” look without manually authoring every slice. Steps <= 0 defaults to one painted segment.

PaintSweepArc provides the same behavior through a convenience parameter list.

For a runnable end-to-end example, see ../samples/test_021_gradients.go.