canvas

package
v0.0.10 Latest Latest
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 Go to latest Published: Jun 2, 2026 License: MIT Imports: 13 Imported by: 0

Documentation

Overview

Package canvas defines the rendering backend abstraction. All drawing operations go through the Canvas interface, which decouples geometry rendering from the specific graphics library (gogpu/gg, SVG, etc.).

Index

Constants

View Source 
const (
	ShapeCircle       = "circle"
	ShapeSquare       = "square"
	ShapeTriangle     = "triangle"
	ShapeTriangleDown = "triangleDown"
	ShapeDiamond      = "diamond"
	ShapePlus         = "plus"
	ShapeCross        = "cross"
	ShapeStar         = "star"
	ShapePentagon     = "pentagon"
	ShapeHexagon      = "hexagon"
)

Shape name constants — single source of truth for all shape identifiers used throughout the library (scales, drawers, legends, canvas backends).

Variables

View Source 
var (
	AnchorTopLeft      = TextAnchor{0, 0}
	AnchorTopCenter    = TextAnchor{0.5, 0}
	AnchorTopRight     = TextAnchor{1, 0}
	AnchorMiddleLeft   = TextAnchor{0, 0.5}
	AnchorCenter       = TextAnchor{0.5, 0.5}
	AnchorMiddleRight  = TextAnchor{1, 0.5}
	AnchorBottomLeft   = TextAnchor{0, 1}
	AnchorBottomCenter = TextAnchor{0.5, 1}
	AnchorBottomRight  = TextAnchor{1, 1}
)

Common text anchors.

Functions

func DrawShapePath added in v0.0.8 

func DrawShapePath(c Canvas, shape string, cx, cy, r float64)

DrawShapePath constructs a shape path using the Canvas path API. This is the fallback implementation used by RecordingCanvas and other backends that do not have native polygon primitives. RasterCanvas uses gg.Context.DrawRegularPolygon directly instead — see RasterCanvas.DrawShape.

func ExportPDF 

func ExportPDF(r *recording.Recording, w io.Writer) (int64, error)

ExportPDF replays a recording into the native PDF backend and writes to w.

func ExportSVG 

func ExportSVG(r *recording.Recording, w io.Writer) (int64, error)

ExportSVG replays a recording into the native SVG backend and writes to w.

func IsStrokeShape added in v0.0.8 

func IsStrokeShape(shape string) bool

IsStrokeShape reports whether the shape should be rendered with stroke rather than fill (i.e., line-based shapes).

func Shapes added in v0.0.8 

func Shapes() []string

Shapes returns the ordered list of all supported shape names. The order matches the default cycle used by [scale.ShapeScale].

Types

type Canvas 

type Canvas interface {

	// Save pushes the current graphics state (color, transform, clip) onto a stack.
	Save()
	// Restore pops the graphics state stack.
	Restore()

	// Translate shifts the origin by (dx, dy).
	Translate(dx, dy float64)
	// Rotate applies a rotation of angle radians around the current origin.
	Rotate(angle float64)
	// ScaleXY applies a non-uniform scale.
	ScaleXY(sx, sy float64)

	// MoveTo starts a new sub-path at (x, y).
	MoveTo(x, y float64)
	// LineTo adds a line segment from the current point to (x, y).
	LineTo(x, y float64)
	// QuadraticTo adds a quadratic Bézier curve to (x, y) via control point (cx, cy).
	QuadraticTo(cx, cy, x, y float64)
	// CubicTo adds a cubic Bézier curve to (x, y) via control points (cx1, cy1) and (cx2, cy2).
	CubicTo(cx1, cy1, cx2, cy2, x, y float64)
	// ClosePath closes the current sub-path with a line to the start point.
	ClosePath()
	// ClearPath discards the current path without drawing.
	ClearPath()

	// SetColor sets the current drawing color for both fill and stroke.
	SetColor(c color.Color)
	// SetRGBA sets the current drawing color from normalized components.
	SetRGBA(r, g, b, a float64)
	// SetLineWidth sets the stroke width in pixels.
	SetLineWidth(w float64)
	// SetLineDash sets the dash pattern. Pass nil or empty for solid lines.
	SetLineDash(pattern ...float64)
	// Fill fills the current path with the current color, then clears the path.
	Fill()
	// Stroke draws the current path outline, then clears the path.
	Stroke()
	// FillPreserve fills without clearing the path (allows subsequent stroke).
	FillPreserve()
	// Clip clips rendering to the current path. Call after constructing a path
	// (e.g. DrawRectangle). Use Save/Restore to undo the clip.
	Clip()
	// ClipRect clips rendering to the axis-aligned rectangle (x, y, w, h).
	// This is much faster than DrawRectangle+Clip for rectangular clip regions
	// because the backend can use a GPU scissor rect instead of rasterizing
	// a full-resolution clip mask.
	ClipRect(x, y, w, h float64)

	// DrawCircle adds a circle path centered at (cx, cy) with radius r.
	DrawCircle(cx, cy, r float64)
	// DrawRectangle adds a rectangle path at (x, y) with dimensions (w, h).
	DrawRectangle(x, y, w, h float64)
	// DrawLine adds a line path from (x1, y1) to (x2, y2).
	DrawLine(x1, y1, x2, y2 float64)
	// DrawShape adds a path for the specified shape centered at (cx, cy) with size/radius r.
	// Supported shapes: "circle", "square", "triangle", "diamond", "triangleDown",
	// "plus", "cross", "star", "pentagon", "hexagon".
	DrawShape(shape string, cx, cy, r float64)

	// SetFontSize sets the font size in points.
	SetFontSize(size float64)
	// SetTabularNums enables or disables tabular (monospaced) digit widths
	// for subsequent text rendering. When enabled, digits occupy uniform
	// horizontal space for aligned numeric columns (e.g., axis tick labels).
	// Backends that don't support OpenType features may ignore this.
	SetTabularNums(enabled bool)
	// DrawStringAnchored draws text at (x, y) with anchor (ax, ay) ∈ [0,1].
	// (0,0) = top-left, (0.5,0.5) = center, (1,1) = bottom-right.
	DrawStringAnchored(text string, x, y, ax, ay float64)
	// MeasureString returns the width and height of the rendered text.
	MeasureString(text string) (w, h float64)

	// Clear fills the entire canvas with the given color.
	Clear(c color.Color)
	// Width returns the canvas width in pixels.
	Width() int
	// Height returns the canvas height in pixels.
	Height() int
	// DrawImage composites the given image onto the canvas at position (x, y).
	// Used for compositing panel sub-canvases during parallel rendering.
	DrawImage(img image.Image, x, y float64)

	// Close releases backend resources (GPU buffers, etc.).
	// Implementations that hold no resources may return nil.
	Close() error
}

Canvas is the core rendering abstraction. Implementations provide the actual drawing primitives targeting specific backends (CPU rasterizer, GPU pipeline, SVG writer, etc.).

The API is modeled after gogpu/gg's Context for natural integration, but abstracted so alternative backends can be swapped without changing any rendering logic.

type FontWeight 

type FontWeight int

FontWeight describes font weight for text rendering. 

const (
	WeightNormal FontWeight = 400
	WeightBold   FontWeight = 700
)

FontWeight constants for common weights.

type RasterCanvas added in v0.0.10 

type RasterCanvas struct {
	// contains filtered or unexported fields
}

RasterCanvas wraps a gogpu/gg.Context to implement the Canvas interface. This is the primary CPU-based rendering backend.

func NewRasterCanvas added in v0.0.10 

func NewRasterCanvas(width, height int) *RasterCanvas

NewRasterCanvas creates a Canvas backed by a gogpu/gg rasterizer.

func NewRasterCanvasCPU added in v0.0.10 

func NewRasterCanvasCPU(width, height int) *RasterCanvas

NewRasterCanvasCPU creates a Canvas that uses pure-CPU analytic rasterization, bypassing the GPU accelerator. This produces deterministic output even when multiple canvases are created in a single process (useful for tests).

func RasterFromContext added in v0.0.10 

func RasterFromContext(ctx *gg.Context) *RasterCanvas

RasterFromContext wraps an existing gg.Context.

func (*RasterCanvas) Clear added in v0.0.10 

func (c *RasterCanvas) Clear(col color.Color)

Clear fills the entire canvas with the given color. Uses DrawRectangle+Fill instead of ctx.Clear() because the GPU accelerator needs a draw command to update the surface — ctx.Clear() only writes to the CPU pixmap and leaves the GPU surface stale.

func (*RasterCanvas) ClearPath added in v0.0.10 

func (c *RasterCanvas) ClearPath()

ClearPath discards the current path without drawing.

func (*RasterCanvas) Clip added in v0.0.10 

func (c *RasterCanvas) Clip()

Clip clips rendering to the current path.

func (*RasterCanvas) ClipRect added in v0.0.10 

func (c *RasterCanvas) ClipRect(x, y, w, h float64)

ClipRect clips rendering to the axis-aligned rectangle (x, y, w, h). Uses gg.Context.ClipRect which pushes a rect onto the clip stack without rasterizing a full-resolution anti-aliased clip mask. Profile showed the generic Clip() path consuming ~75% of frame time via MaskClipper.rasterizeScanlineAA — this bypasses that entirely.

func (*RasterCanvas) Close added in v0.0.10 

func (c *RasterCanvas) Close() error

Close releases the underlying gg.Context's GPU resources. Always call Close (or use defer) when the canvas is no longer needed to avoid GPU resource leaks (wgpu BindGroup/Buffer finalizer warnings).

func (*RasterCanvas) ClosePath added in v0.0.10 

func (c *RasterCanvas) ClosePath()

ClosePath closes the current sub-path.

func (*RasterCanvas) Context added in v0.0.10 

func (c *RasterCanvas) Context() *gg.Context

Context returns the underlying gg.Context for direct access when needed (e.g., font loading, image export).

func (*RasterCanvas) CubicTo added in v0.0.10 

func (c *RasterCanvas) CubicTo(cx1, cy1, cx2, cy2, x, y float64)

CubicTo adds a cubic Bézier curve via (cx1, cy1) and (cx2, cy2) to (x, y).

func (*RasterCanvas) DrawCircle added in v0.0.10 

func (c *RasterCanvas) DrawCircle(cx, cy, r float64)

DrawCircle adds a circle path centered at (cx, cy) with radius r.

func (*RasterCanvas) DrawImage added in v0.0.10 

func (c *RasterCanvas) DrawImage(img image.Image, x, y float64)

DrawImage composites img onto the canvas at pixel position (x, y).

func (*RasterCanvas) DrawLine added in v0.0.10 

func (c *RasterCanvas) DrawLine(x1, y1, x2, y2 float64)

DrawLine adds a line path from (x1, y1) to (x2, y2).

func (*RasterCanvas) DrawRectangle added in v0.0.10 

func (c *RasterCanvas) DrawRectangle(x, y, w, h float64)

DrawRectangle adds a rectangle path at (x, y) with dimensions (w, h).

func (*RasterCanvas) DrawShape added in v0.0.10 

func (c *RasterCanvas) DrawShape(shape string, cx, cy, r float64)

DrawShape adds a path for the specified shape centered at (cx, cy) with size/radius r. Uses gg.Context.DrawRegularPolygon for polygon shapes for optimal rendering.

func (*RasterCanvas) DrawStringAnchored added in v0.0.10 

func (c *RasterCanvas) DrawStringAnchored(s string, x, y, ax, ay float64)

DrawStringAnchored draws text at (x, y) with anchor (ax, ay).

func (*RasterCanvas) EncodePNG added in v0.0.10 

func (c *RasterCanvas) EncodePNG(w io.Writer) error

EncodePNG writes the canvas as PNG to the given writer.

func (*RasterCanvas) Fill added in v0.0.10 

func (c *RasterCanvas) Fill()

Fill fills the current path with the current color, then clears the path.

func (*RasterCanvas) FillPreserve added in v0.0.10 

func (c *RasterCanvas) FillPreserve()

FillPreserve fills without clearing the path (allows subsequent stroke).

func (*RasterCanvas) Height added in v0.0.10 

func (c *RasterCanvas) Height() int

Height returns the canvas height in pixels.

func (*RasterCanvas) Image added in v0.0.10 

func (c *RasterCanvas) Image() image.Image

Image returns the underlying image.

func (*RasterCanvas) LineTo added in v0.0.10 

func (c *RasterCanvas) LineTo(x, y float64)

LineTo adds a line segment from the current point to (x, y).

func (*RasterCanvas) MeasureString added in v0.0.10 

func (c *RasterCanvas) MeasureString(s string) (float64, float64)

MeasureString returns the width and height of the rendered text.

func (*RasterCanvas) MoveTo added in v0.0.10 

func (c *RasterCanvas) MoveTo(x, y float64)

MoveTo starts a new sub-path at (x, y).

func (*RasterCanvas) QuadraticTo added in v0.0.10 

func (c *RasterCanvas) QuadraticTo(cx, cy, x, y float64)

QuadraticTo adds a quadratic Bézier curve via control point (cx, cy) to (x, y).

func (*RasterCanvas) Restore added in v0.0.10 

func (c *RasterCanvas) Restore()

Restore pops the graphics state from the stack.

func (*RasterCanvas) Rotate added in v0.0.10 

func (c *RasterCanvas) Rotate(angle float64)

Rotate applies a rotation of angle radians.

func (*RasterCanvas) Save added in v0.0.10 

func (c *RasterCanvas) Save()

Save pushes the current graphics state onto the stack.

func (*RasterCanvas) SavePNG added in v0.0.10 

func (c *RasterCanvas) SavePNG(path string) error

SavePNG writes the canvas to a PNG file.

func (*RasterCanvas) ScaleXY added in v0.0.10 

func (c *RasterCanvas) ScaleXY(sx, sy float64)

ScaleXY applies a non-uniform scale.

func (*RasterCanvas) SetColor added in v0.0.10 

func (c *RasterCanvas) SetColor(col color.Color)

SetColor sets the current drawing color for both fill and stroke.

func (*RasterCanvas) SetFontSize added in v0.0.10 

func (c *RasterCanvas) SetFontSize(size float64)

SetFontSize resolves the best available font at the given size. Resolution order: system font via fonts resolver -> embedded Go Regular fallback.

func (*RasterCanvas) SetLineDash added in v0.0.10 

func (c *RasterCanvas) SetLineDash(pattern ...float64)

SetLineDash sets the dash pattern. Pass nil or empty for solid lines.

func (*RasterCanvas) SetLineWidth added in v0.0.10 

func (c *RasterCanvas) SetLineWidth(w float64)

SetLineWidth sets the stroke width in pixels.

func (*RasterCanvas) SetRGBA added in v0.0.10 

func (c *RasterCanvas) SetRGBA(r, g, b, a float64)

SetRGBA sets the current drawing color from normalized components.

func (*RasterCanvas) SetTabularNums added in v0.0.10 

func (c *RasterCanvas) SetTabularNums(enabled bool)

SetTabularNums enables or disables tabular (monospaced) digit widths.

func (*RasterCanvas) Stroke added in v0.0.10 

func (c *RasterCanvas) Stroke()

Stroke draws the current path outline, then clears the path.

func (*RasterCanvas) Translate added in v0.0.10 

func (c *RasterCanvas) Translate(dx, dy float64)

Translate shifts the origin by (dx, dy).

func (*RasterCanvas) Width added in v0.0.10 

func (c *RasterCanvas) Width() int

Width returns the canvas width in pixels.

type RecordingCanvas 

type RecordingCanvas struct {
	// contains filtered or unexported fields
}

RecordingCanvas wraps a recording.Recorder to implement the Canvas interface. All drawing operations are captured as a recording that can later be replayed into any backend (SVG, PDF, raster, etc.) via [Recording.Playback].

func NewRecordingCanvas 

func NewRecordingCanvas(width, height int) *RecordingCanvas

NewRecordingCanvas creates a Canvas that records all drawing operations. After rendering, call RecordingCanvas.FinishRecording and replay into the desired backend (e.g., SVG, PDF).

func (*RecordingCanvas) Clear 

func (c *RecordingCanvas) Clear(col color.Color)

Clear fills the entire canvas with the given color.

func (*RecordingCanvas) ClearPath 

func (c *RecordingCanvas) ClearPath()

ClearPath discards the current path without drawing.

func (*RecordingCanvas) Clip 

func (c *RecordingCanvas) Clip()

Clip clips rendering to the current path.

func (*RecordingCanvas) ClipRect added in v0.0.10 

func (c *RecordingCanvas) ClipRect(x, y, w, h float64)

ClipRect clips rendering to the axis-aligned rectangle (x, y, w, h). Falls back to DrawRectangle+Clip since recording.Recorder does not have a dedicated ClipRect. This is acceptable because RecordingCanvas is used for SVG/PDF export, not interactive rendering.

func (*RecordingCanvas) Close added in v0.0.5 

func (c *RecordingCanvas) Close() error

Close is a no-op for RecordingCanvas (no GPU resources to release).

func (*RecordingCanvas) ClosePath 

func (c *RecordingCanvas) ClosePath()

ClosePath closes the current sub-path.

func (*RecordingCanvas) CubicTo 

func (c *RecordingCanvas) CubicTo(cx1, cy1, cx2, cy2, x, y float64)

CubicTo adds a cubic Bézier curve via (cx1, cy1) and (cx2, cy2) to (x, y).

func (*RecordingCanvas) DrawCircle 

func (c *RecordingCanvas) DrawCircle(cx, cy, r float64)

DrawCircle adds a circle path centered at (cx, cy) with radius r.

func (*RecordingCanvas) DrawImage added in v0.0.6 

func (c *RecordingCanvas) DrawImage(_ image.Image, _, _ float64)

DrawImage is a no-op for RecordingCanvas. SVG/PDF recording does not support raster compositing; parallel panel rendering is only used by raster backends (RasterCanvas).

func (*RecordingCanvas) DrawLine 

func (c *RecordingCanvas) DrawLine(x1, y1, x2, y2 float64)

DrawLine adds a line path from (x1, y1) to (x2, y2).

func (*RecordingCanvas) DrawRectangle 

func (c *RecordingCanvas) DrawRectangle(x, y, w, h float64)

DrawRectangle adds a rectangle path at (x, y) with dimensions (w, h).

func (*RecordingCanvas) DrawShape added in v0.0.8 

func (c *RecordingCanvas) DrawShape(shape string, cx, cy, r float64)

DrawShape adds a path for the specified shape centered at (cx, cy) with size/radius r.

func (*RecordingCanvas) DrawStringAnchored 

func (c *RecordingCanvas) DrawStringAnchored(s string, x, y, ax, ay float64)

DrawStringAnchored draws text at (x, y) with anchor (ax, ay).

The anchor is pre-applied here rather than deferred to the recorder: the recording playback drops the anchor (its Backend.DrawText takes no anchor and is handed a nil face), so anchored text would otherwise render left-aligned at the baseline in SVG/PDF. We replicate gg's exact anchor math against the current face and record a base-positioned DrawString, keeping vector text aligned with the raster output.

func (*RecordingCanvas) Fill 

func (c *RecordingCanvas) Fill()

Fill fills the current path with the current color, then clears the path.

func (*RecordingCanvas) FillPreserve 

func (c *RecordingCanvas) FillPreserve()

FillPreserve fills without clearing the path (allows subsequent stroke).

func (*RecordingCanvas) FinishRecording 

func (c *RecordingCanvas) FinishRecording() *recording.Recording

FinishRecording completes the recording and returns the captured operations.

func (*RecordingCanvas) Height 

func (c *RecordingCanvas) Height() int

Height returns the canvas height in pixels.

func (*RecordingCanvas) LineTo 

func (c *RecordingCanvas) LineTo(x, y float64)

LineTo adds a line segment from the current point to (x, y).

func (*RecordingCanvas) MeasureString 

func (c *RecordingCanvas) MeasureString(s string) (float64, float64)

MeasureString returns the width and height of the rendered text.

func (*RecordingCanvas) MoveTo 

func (c *RecordingCanvas) MoveTo(x, y float64)

MoveTo starts a new sub-path at (x, y).

func (*RecordingCanvas) QuadraticTo 

func (c *RecordingCanvas) QuadraticTo(cx, cy, x, y float64)

QuadraticTo adds a quadratic Bézier curve via control point (cx, cy) to (x, y).

func (*RecordingCanvas) Restore 

func (c *RecordingCanvas) Restore()

Restore pops the graphics state from the stack.

func (*RecordingCanvas) Rotate 

func (c *RecordingCanvas) Rotate(angle float64)

Rotate applies a rotation of angle radians.

func (*RecordingCanvas) Save 

func (c *RecordingCanvas) Save()

Save pushes the current graphics state onto the stack.

func (*RecordingCanvas) ScaleXY 

func (c *RecordingCanvas) ScaleXY(sx, sy float64)

ScaleXY applies a non-uniform scale.

func (*RecordingCanvas) SetColor 

func (c *RecordingCanvas) SetColor(col color.Color)

SetColor sets the current drawing color for both fill and stroke.

func (*RecordingCanvas) SetFontSize 

func (c *RecordingCanvas) SetFontSize(size float64)

SetFontSize resolves the best available font at the given size.

func (*RecordingCanvas) SetLineDash 

func (c *RecordingCanvas) SetLineDash(pattern ...float64)

SetLineDash sets the dash pattern. Pass nil or empty for solid lines.

func (*RecordingCanvas) SetLineWidth 

func (c *RecordingCanvas) SetLineWidth(w float64)

SetLineWidth sets the stroke width in pixels.

func (*RecordingCanvas) SetRGBA 

func (c *RecordingCanvas) SetRGBA(r, g, b, a float64)

SetRGBA sets the current drawing color from normalized components.

func (*RecordingCanvas) SetTabularNums added in v0.0.5 

func (c *RecordingCanvas) SetTabularNums(enabled bool)

SetTabularNums enables or disables tabular (monospaced) digit widths.

func (*RecordingCanvas) Stroke 

func (c *RecordingCanvas) Stroke()

Stroke draws the current path outline, then clears the path.

func (*RecordingCanvas) Translate 

func (c *RecordingCanvas) Translate(dx, dy float64)

Translate shifts the origin by (dx, dy).

func (*RecordingCanvas) Width 

func (c *RecordingCanvas) Width() int

Width returns the canvas width in pixels.

type TextAnchor 

type TextAnchor struct {
	X, Y float64 // [0,1] where (0,0) = top-left, (1,1) = bottom-right
}

TextAnchor defines text alignment as normalized coordinates.

Source Files

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Directories

Path Synopsis
Package gpu opts in GPU acceleration.
 Package gpu opts in GPU acceleration.

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