draw.go

// 13 december 2015

package ui

// #include <stdlib.h>
// #include "ui.h"
// static uiDrawBrush *newBrush(void)
// {
// 	uiDrawBrush *b;
// 
// 	b = (uiDrawBrush *) malloc(sizeof (uiDrawBrush));
// 	// TODO
// 	return b;
// }
// static uiDrawBrushGradientStop *newStops(size_t n)
// {
// 	uiDrawBrushGradientStop *stops;
// 
// 	stops = (uiDrawBrushGradientStop *) malloc(n * sizeof (uiDrawBrushGradientStop));
// 	// TODO
// 	return stops;
// }
// static void setStop(uiDrawBrushGradientStop *stops, size_t i, double pos, double r, double g, double b, double a)
// {
// 	stops[i].Pos = pos;
// 	stops[i].R = r;
// 	stops[i].G = g;
// 	stops[i].B = b;
// 	stops[i].A = a;
// }
// static void freeBrush(uiDrawBrush *b)
// {
// 	if (b->Type == uiDrawBrushTypeLinearGradient || b->Type == uiDrawBrushTypeRadialGradient)
// 		free(b->Stops);
// 	free(b);
// }
// static uiDrawStrokeParams *newStrokeParams(void)
// {
// 	uiDrawStrokeParams *b;
// 
// 	b = (uiDrawStrokeParams *) malloc(sizeof (uiDrawStrokeParams));
// 	// TODO
// 	return b;
// }
// static double *newDashes(size_t n)
// {
// 	double *dashes;
// 
// 	dashes = (double *) malloc(n * sizeof (double));
// 	// TODO
// 	return dashes;
// }
// static void setDash(double *dashes, size_t i, double dash)
// {
// 	dashes[i] = dash;
// }
// static void freeStrokeParams(uiDrawStrokeParams *sp)
// {
// 	if (sp->Dashes != NULL)
// 		free(sp->Dashes);
// 	free(sp);
// }
// static uiDrawMatrix *newMatrix(void)
// {
// 	uiDrawMatrix *m;
// 
// 	m = (uiDrawMatrix *) malloc(sizeof (uiDrawMatrix));
// 	// TODO
// 	return m;
// }
// static void freeMatrix(uiDrawMatrix *m)
// {
// 	free(m);
// }
import "C"

// BUG(andlabs): Ideally, all the drawing APIs should be in another package ui/draw (they all have the "uiDraw" prefix in C to achieve a similar goal of avoiding confusing programmers via namespace pollution); managing the linkage of the libui shared library itself across multiple packages is likely going to be a pain, though. (Custom controls implemented using libui won't have this issue, as they *should* only need libui present when linking the shared object, not when linking the Go wrapper. I'm not sure; I'd have to find out first.)

// Path represents a geometric path in a drawing context.
// This is the basic unit of drawing: all drawing operations consist of
// forming a path, then stroking, filling, or clipping to that path.
// A path is an OS resource; you must explicitly free it when finished.
// Paths consist of multiple figures. Once you have added all the
// figures to a path, you must "end" the path to make it ready to draw
// with.
// TODO rewrite all that
// 
// Or more visually, the lifecycle of a Path is
// 	p := NewPath()
// 	for every figure {
// 		p.NewFigure(...) // or NewFigureWithArc
// 		p.LineTo(...)    // any number of these in any order
// 		p.ArcTo(...)
// 		p.BezierTo(...)
// 		if figure should be closed {
// 			p.CloseFigure()
// 		}
// 	}
// 	p.End()
// 	// ...
// 	dp.Context.Stroke(p, ...) // any number of these in any order
// 	dp.Context.Fill(p, ...)
// 	dp.Context.Clip(p)
// 	// ...
// 	p.Free() // when done with the path
// 
// A Path also defines its fill mode. (This should ideally be a fill
// parameter, but some implementations prevent it.)
// TODO talk about fill modes
type Path struct {
	p	*C.uiDrawPath
}

// TODO
type FillMode uint
const (
	Winding FillMode = iota
	Alternate
)

// NewPath creates a new Path with the given fill mode.
func NewPath(fillMode FillMode) *Path {
	var fm C.uiDrawFillMode

	switch fillMode {
	case Winding:
		fm = C.uiDrawFillModeWinding
	case Alternate:
		fm = C.uiDrawFillModeAlternate
	default:
		panic("invalid fill mode passed to ui.NewPath()")
	}
	return &Path{
		p:	C.uiDrawNewPath(fm),
	}
}

// Free destroys a Path. After calling Free the Path cannot be used.
func (p *Path) Free() {
	C.uiDrawFreePath(p.p)
}

// NewFigure starts a new figure in the Path. The current point
// is set to the given point.
func (p *Path) NewFigure(x float64, y float64) {
	C.uiDrawPathNewFigure(p.p, C.double(x), C.double(y))
}

// NewFigureWithArc starts a new figure in the Path and adds an arc
// as the first element of the figure. Unlike ArcTo, NewFigureWithArc
// does not draw an initial line segment. Otherwise, see ArcTo.
func (p *Path) NewFigureWithArc(xCenter float64, yCenter float64, radius float64, startAngle float64, sweep float64, isNegative bool) {
	C.uiDrawPathNewFigureWithArc(p.p,
		C.double(xCenter), C.double(yCenter),
		C.double(radius),
		C.double(startAngle), C.double(sweep),
		frombool(isNegative))
}

// LineTo adds a line to the current figure of the Path starting from
// the current point and ending at the given point. The current point
// is set to the ending point.
func (p *Path) LineTo(x float64, y float64) {
	C.uiDrawPathLineTo(p.p, C.double(x), C.double(y))
}

// ArcTo adds a circular arc to the current figure of the Path.
// You pass it the center of the arc, its radius in radians, the starting
// angle (couterclockwise) in radians, and the number of radians the
// arc should sweep (counterclockwise). A line segment is drawn from
// the current point to the start of the arc. The current point is set to
// the end of the arc.
func (p *Path) ArcTo(xCenter float64, yCenter float64, radius float64, startAngle float64, sweep float64, isNegative bool) {
	C.uiDrawPathArcTo(p.p,
		C.double(xCenter), C.double(yCenter),
		C.double(radius),
		C.double(startAngle), C.double(sweep),
		frombool(isNegative))
}

// BezierTo adds a cubic Bezier curve to the current figure of the Path.
// Its start point is the current point. c1x and c1y are the first control
// point. c2x and c2y are the second control point. endX and endY
// are the end point. The current point is set to the end point.
func (p *Path) BezierTo(c1x float64, c1y float64, c2x float64, c2y float64, endX float64, endY float64) {
	C.uiDrawPathBezierTo(p.p,
		C.double(c1x), C.double(c1y),
		C.double(c2x), C.double(c2y),
		C.double(endX), C.double(endY))
}

// CloseFigure draws a line segment from the current point of the
// current figure of the Path back to its initial point. After calling this,
// the current figure is over and you must either start a new figure
// or end the Path. If this is not called and you start a new figure or
// end the Path, then the current figure will not have this closing line
// segment added to it (but the figure will still be over).
func (p *Path) CloseFigure() {
	C.uiDrawPathCloseFigure(p.p)
}

// AddRectangle creates a new figure in the Path that consists entirely
// of a rectangle whose top-left corner is at the given point and whose
// size is the given size. The rectangle is a closed figure; you must
// either start a new figure or end the Path after calling this method.
func (p *Path) AddRectangle(x float64, y float64, width float64, height float64) {
	C.uiDrawPathAddRectangle(p.p, C.double(x), C.double(y), C.double(width), C.double(height))
}

// End ends the current Path. You cannot add figures to a Path that has
// been ended. You cannot draw with a Path that has not been ended.
func (p *Path) End() {
	C.uiDrawPathEnd(p.p)
}

// DrawContext represents a drawing surface that you can draw to.
// At present the only DrawContexts are surfaces associated with
// Areas and are provided by package ui; see AreaDrawParams.
type DrawContext struct {
	c	*C.uiDrawContext
}

// BrushType defines the various types of brushes.
// 
// TODO disclaimer
type BrushType int
const (
	Solid BrushType = iota
	LinearGradient
	RadialGradient
	Image		// presently unimplemented
)

// TODO
// 
// TODO disclaimer
type LineCap int
const (
	FlatCap LineCap = iota
	RoundCap
	SquareCap
)

// TODO
// 
// TODO disclaimer
type LineJoin int
const (
	MiterJoin LineJoin = iota
	RoundJoin
	BevelJoin
)

// TODO document
const DefaultMiterLimit = 10.0

// TODO
type Brush struct {
	Type		BrushType

	// If Type is Solid.
	// TODO
	R		float64
	G		float64
	B		float64
	A		float64

	// If Type is LinearGradient or RadialGradient.
	// TODO
	X0			float64	// start point for both
	Y0			float64
	X1			float64	// linear: end point; radial: circle center
	Y1			float64
	OuterRadius	float64	// for radial gradients only
	Stops		[]GradientStop
}

// TODO
type GradientStop struct {
	Pos	float64		// between 0 and 1 inclusive
	R	float64
	G	float64
	B	float64
	A	float64
}

func (b *Brush) toC() *C.uiDrawBrush {
	cb := C.newBrush()
	cb.Type = C.uiDrawBrushType(b.Type)
	switch b.Type {
	case Solid:
		cb.R = C.double(b.R)
		cb.G = C.double(b.G)
		cb.B = C.double(b.B)
		cb.A = C.double(b.A)
	case LinearGradient, RadialGradient:
		cb.X0 = C.double(b.X0)
		cb.Y0 = C.double(b.Y0)
		cb.X1 = C.double(b.X1)
		cb.Y1 = C.double(b.Y1)
		cb.OuterRadius = C.double(b.OuterRadius)
		cb.NumStops = C.size_t(len(b.Stops))
		cb.Stops = C.newStops(cb.NumStops)
		for i, s := range b.Stops {
			C.setStop(cb.Stops, C.size_t(i),
				C.double(s.Pos),
				C.double(s.R),
				C.double(s.G),
				C.double(s.B),
				C.double(s.A))
		}
	case Image:
		panic("unimplemented")
	default:
		panic("invalid brush type in Brush.toC()")
	}
	return cb
}

// TODO
type StrokeParams struct {
	Cap			LineCap
	Join			LineJoin
	Thickness		float64
	MiterLimit		float64
	Dashes		[]float64
	DashPhase	float64
}

func (sp *StrokeParams) toC() *C.uiDrawStrokeParams {
	csp := C.newStrokeParams()
	csp.Cap = C.uiDrawLineCap(sp.Cap)
	csp.Join = C.uiDrawLineJoin(sp.Join)
	csp.Thickness = C.double(sp.Thickness)
	csp.MiterLimit = C.double(sp.MiterLimit)
	csp.Dashes = nil
	csp.NumDashes = C.size_t(len(sp.Dashes))
	if csp.NumDashes != 0 {
		csp.Dashes = C.newDashes(csp.NumDashes)
		for i, d := range sp.Dashes {
			C.setDash(csp.Dashes, C.size_t(i), C.double(d))
		}
	}
	csp.DashPhase = C.double(sp.DashPhase)
	return csp
}

// TODO
func (c *DrawContext) Stroke(p *Path, b *Brush, sp *StrokeParams) {
	cb := b.toC()
	csp := sp.toC()
	C.uiDrawStroke(c.c, p.p, cb, csp)
	C.freeBrush(cb)
	C.freeStrokeParams(csp)
}

// TODO
func (c *DrawContext) Fill(p *Path, b *Brush) {
	cb := b.toC()
	C.uiDrawFill(c.c, p.p, cb)
	C.freeBrush(cb)
}

// TODO
type Matrix struct {
	M11		float64
	M12		float64
	M21		float64
	M22		float64
	M31		float64
	M32		float64
}

// TODO identity matrix
func NewMatrix() *Matrix {
	m := new(Matrix)
	m.SetIdentity()
	return m
}

// TODO
func (m *Matrix) SetIdentity() {
	m.M11 = 1
	m.M12 = 0
	m.M21 = 0
	m.M22 = 1
	m.M31 = 0
	m.M32 = 0
}

func (m *Matrix) toC() *C.uiDrawMatrix {
	cm := C.newMatrix()
	cm.M11 = C.double(m.M11)
	cm.M12 = C.double(m.M12)
	cm.M21 = C.double(m.M21)
	cm.M22 = C.double(m.M22)
	cm.M31 = C.double(m.M31)
	cm.M32 = C.double(m.M32)
	return cm
}

func (m *Matrix) fromC(cm *C.uiDrawMatrix) {
	m.M11 = float64(cm.M11)
	m.M12 = float64(cm.M12)
	m.M21 = float64(cm.M21)
	m.M22 = float64(cm.M22)
	m.M31 = float64(cm.M31)
	m.M32 = float64(cm.M32)
	C.freeMatrix(cm)
}

// TODO
func (m *Matrix) Translate(x float64, y float64) {
	cm := m.toC()
	C.uiDrawMatrixTranslate(cm, C.double(x), C.double(y))
	m.fromC(cm)
}

// TODO
func (m *Matrix) Scale(xCenter float64, yCenter float64, x float64, y float64) {
	cm := m.toC()
	C.uiDrawMatrixScale(cm,
		C.double(xCenter), C.double(yCenter),
		C.double(x), C.double(y))
	m.fromC(cm)
}

// TODO
func (m *Matrix) Rotate(x float64, y float64, amount float64) {
	cm := m.toC()
	C.uiDrawMatrixRotate(cm, C.double(x), C.double(y), C.double(amount))
	m.fromC(cm)
}

// TODO
func (m *Matrix) Skew(x float64, y float64, xamount float64, yamount float64) {
	cm := m.toC()
	C.uiDrawMatrixSkew(cm,
		C.double(x), C.double(y),
		C.double(xamount), C.double(yamount))
	m.fromC(cm)
}

// TODO
func (m *Matrix) Multiply(m2 *Matrix) {
	cm := m.toC()
	cm2 := m2.toC()
	C.uiDrawMatrixMultiply(cm, cm2)
	C.freeMatrix(cm2)
	m.fromC(cm)
}

// TODO
func (m *Matrix) Invertible() bool {
	cm := m.toC()
	res := C.uiDrawMatrixInvertible(cm)
	C.freeMatrix(cm)
	return tobool(res)
}

// TODO
// 
// If m is not invertible, false is returned and m is left unchanged.
func (m *Matrix) Invert() bool {
	cm := m.toC()
	res := C.uiDrawMatrixInvert(cm)
	m.fromC(cm)
	return tobool(res)
}

// TODO unimplemented
func (m *Matrix) TransformPoint(x float64, y float64) (xout float64, yout float64) {
	panic("TODO")
}

// TODO unimplemented
func (m *Matrix) TransformSize(x float64, y float64) (xout float64, yout float64) {
	panic("TODO")
}

// TODO
func (c *DrawContext) Transform(m *Matrix) {
	cm := m.toC()
	C.uiDrawTransform(c.c, cm)
	C.freeMatrix(cm)
}

// TODO
func (c *DrawContext) Clip(p *Path) {
	C.uiDrawClip(c.c, p.p)
}

// TODO
func (c *DrawContext) Save() {
	C.uiDrawSave(c.c)
}

// TODO
func (c *DrawContext) Restore() {
	C.uiDrawRestore(c.c)
}

// FontFamilies represents an enumerator over the font families
// available for use by package ui. A FontFamilies object behaves
// similarly to a []string, except that since family names are loaded
// on demand (depending on the operating system), it is not an
// actual []string. You call ListFontFamilies to obtain a FontFamilies
// object, which should reflect the available fonts at the time of the
// call (TODO verify). Use NumFamilies to get the number of families,
// and Family to get the name of a given family by index. When
// finished, call Free.
// 
// There is no guarantee that the list of families is sorted. You will
// need to do sorting yourself if you need it.
// 
// TODO thread affinity
type FontFamilies struct {
	ff *C.uiDrawFontFamilies
}

// ListFontFamilies creates a new FontFamilies object ready for use.
func ListFontFamilies() *FontFamilies {
	return &FontFamilies{
		ff:	C.uiDrawListFontFamilies(),
	}
}

// Free destroys a FontFamilies. After calling Free, the FontFamilies
// cannot be used.
func (f *FontFamilies) Free() {
	C.uiDrawFreeFontFamilies(f.ff)
}

// NumFamilies returns the number of font families available.
func (f *FontFamilies) NumFamilies() int {
	return int(C.uiDrawFontFamiliesNumFamilies(f.ff))
}

// Family returns the name of the nth family in the list.
func (f *FontFamilies) Family(n int) string {
	cname := C.uiDrawFontFamiliesFamily(f.ff, C.uintmax_t(n))
	name := C.GoString(cname)
	C.uiFreeText(cname)
	return name
}