freetype/raster: new Path and Stroke API.
The stroking algorithm is a placeholder. A proper one will land in a future change once the API is agreed upon. R=r, rsc CC=golang-dev, rog http://codereview.appspot.com/1708045
This commit is contained in:
Nigel Tao
parent
bfc68b0d61
commit
2316e5355d
|
|
@ -7,6 +7,7 @@ include $(GOROOT)/src/Make.$(GOARCH)
|
|||
|
||||
TARG=freetype-go.googlecode.com/hg/freetype/raster
|
||||
GOFILES=\
|
||||
geom.go\
|
||||
paint.go\
|
||||
raster.go\
|
||||
|
||||
|
|
|
|||
260
freetype/raster/geom.go
Normal file
260
freetype/raster/geom.go
Normal file
|
|
@ -0,0 +1,260 @@
|
|||
// Copyright 2010 The Freetype-Go Authors. All rights reserved.
|
||||
// Use of this source code is governed by your choice of either the
|
||||
// FreeType License or the GNU General Public License version 2,
|
||||
// both of which can be found in the LICENSE file.
|
||||
|
||||
package raster
|
||||
|
||||
import (
|
||||
"fmt"
|
||||
"math"
|
||||
)
|
||||
|
||||
// A 24.8 fixed point number.
|
||||
type Fixed int32
|
||||
|
||||
// String returns a human-readable representation of a 24.8 fixed point number.
|
||||
// For example, the number one-and-a-quarter becomes "1:064".
|
||||
func (x Fixed) String() string {
|
||||
i, f := x/256, x%256
|
||||
if f < 0 {
|
||||
f = -f
|
||||
}
|
||||
return fmt.Sprintf("%d:%03d", int32(i), int32(f))
|
||||
}
|
||||
|
||||
// maxAbs returns the maximum of abs(a) and abs(b).
|
||||
func maxAbs(a, b Fixed) Fixed {
|
||||
if a < 0 {
|
||||
a = -a
|
||||
}
|
||||
if b < 0 {
|
||||
b = -b
|
||||
}
|
||||
if a < b {
|
||||
return b
|
||||
}
|
||||
return a
|
||||
}
|
||||
|
||||
// A two-dimensional point or vector, in 24.8 fixed point format.
|
||||
type Point struct {
|
||||
X, Y Fixed
|
||||
}
|
||||
|
||||
// Len returns the length of the vector p.
|
||||
func (p Point) Len() Fixed {
|
||||
// TODO(nigeltao): use fixed point math.
|
||||
x := float64(p.X)
|
||||
y := float64(p.Y)
|
||||
return Fixed(math.Sqrt(x*x + y*y))
|
||||
}
|
||||
|
||||
// Norm returns the vector p normalized to the given length, or the zero Point
|
||||
// if p is degenerate.
|
||||
func (p Point) Norm(length Fixed) Point {
|
||||
d := p.Len()
|
||||
if d == 0 {
|
||||
return Point{0, 0}
|
||||
}
|
||||
// TODO(nigeltao): should we check for overflow?
|
||||
return Point{p.X * length / d, p.Y * length / d}
|
||||
}
|
||||
|
||||
// RotateCW returns the vector p rotated clockwise by 90 degrees.
|
||||
func (p Point) RotateCW() Point {
|
||||
return Point{p.Y, -p.X}
|
||||
}
|
||||
|
||||
// RotateCCW returns the vector p rotated counter-clockwise by 90 degrees.
|
||||
func (p Point) RotateCCW() Point {
|
||||
return Point{-p.Y, p.X}
|
||||
}
|
||||
|
||||
// An Adder accumulates points on a curve.
|
||||
type Adder interface {
|
||||
// Start starts a new curve at the given point.
|
||||
Start(a Point)
|
||||
// Add1 adds a linear segment to the current curve.
|
||||
Add1(b Point)
|
||||
// Add2 adds a quadratic segment to the current curve.
|
||||
Add2(b, c Point)
|
||||
// Add3 adds a cubic segment to the current curve.
|
||||
Add3(b, c, d Point)
|
||||
}
|
||||
|
||||
// A Path is a sequence of curves, and a curve is a start point followed by a
|
||||
// sequence of linear, quadratic or cubic segments.
|
||||
type Path []Fixed
|
||||
|
||||
// String returns a human-readable representation of a Path.
|
||||
func (p Path) String() string {
|
||||
s := ""
|
||||
for i := 0; i < len(p); {
|
||||
if i != 0 {
|
||||
s += " "
|
||||
}
|
||||
switch p[i] {
|
||||
case 0:
|
||||
s += "S0" + fmt.Sprint([]Fixed(p[i+1:i+3]))
|
||||
i += 3
|
||||
case 1:
|
||||
s += "A1" + fmt.Sprint([]Fixed(p[i+1:i+3]))
|
||||
i += 3
|
||||
case 2:
|
||||
s += "A2" + fmt.Sprint([]Fixed(p[i+1:i+5]))
|
||||
i += 5
|
||||
case 3:
|
||||
s += "A3" + fmt.Sprint([]Fixed(p[i+1:i+7]))
|
||||
i += 7
|
||||
default:
|
||||
panic("freetype/raster: bad path")
|
||||
}
|
||||
}
|
||||
return s
|
||||
}
|
||||
|
||||
// grow adds n elements to p.
|
||||
func (p *Path) grow(n int) {
|
||||
n += len(*p)
|
||||
if n > cap(*p) {
|
||||
old := *p
|
||||
*p = make([]Fixed, n, 2*n+8)
|
||||
copy(*p, old)
|
||||
return
|
||||
}
|
||||
*p = (*p)[0:n]
|
||||
}
|
||||
|
||||
// Clear cancels any previous calls to p.Start or p.AddXxx.
|
||||
func (p *Path) Clear() {
|
||||
*p = (*p)[0:0]
|
||||
}
|
||||
|
||||
// Start starts a new curve at the given point.
|
||||
func (p *Path) Start(a Point) {
|
||||
n := len(*p)
|
||||
p.grow(3)
|
||||
(*p)[n] = 0
|
||||
(*p)[n+1] = a.X
|
||||
(*p)[n+2] = a.Y
|
||||
}
|
||||
|
||||
// Add1 adds a linear segment to the current curve.
|
||||
func (p *Path) Add1(b Point) {
|
||||
n := len(*p)
|
||||
p.grow(3)
|
||||
(*p)[n] = 1
|
||||
(*p)[n+1] = b.X
|
||||
(*p)[n+2] = b.Y
|
||||
}
|
||||
|
||||
// Add2 adds a quadratic segment to the current curve.
|
||||
func (p *Path) Add2(b, c Point) {
|
||||
n := len(*p)
|
||||
p.grow(5)
|
||||
(*p)[n] = 2
|
||||
(*p)[n+1] = b.X
|
||||
(*p)[n+2] = b.Y
|
||||
(*p)[n+3] = c.X
|
||||
(*p)[n+4] = c.Y
|
||||
}
|
||||
|
||||
// Add3 adds a cubic segment to the current curve.
|
||||
func (p *Path) Add3(b, c, d Point) {
|
||||
n := len(*p)
|
||||
p.grow(7)
|
||||
(*p)[n] = 3
|
||||
(*p)[n+1] = b.X
|
||||
(*p)[n+2] = b.Y
|
||||
(*p)[n+3] = c.X
|
||||
(*p)[n+4] = c.Y
|
||||
(*p)[n+5] = d.X
|
||||
(*p)[n+6] = d.Y
|
||||
}
|
||||
|
||||
// AddPath adds the Path q to p.
|
||||
func (p *Path) AddPath(q Path) {
|
||||
n, m := len(*p), len(q)
|
||||
p.grow(m)
|
||||
copy((*p)[n:n+m], q)
|
||||
}
|
||||
|
||||
// A Cap signifies how to begin or end a stroked curve.
|
||||
type Cap int
|
||||
|
||||
const (
|
||||
RoundCap Cap = iota
|
||||
ButtCap
|
||||
SquareCap
|
||||
)
|
||||
|
||||
// A Join signifies how to join interior nodes of a stroked curve.
|
||||
type Join int
|
||||
|
||||
const (
|
||||
RoundJoin Join = iota
|
||||
BevelJoin
|
||||
MiterJoin
|
||||
)
|
||||
|
||||
// AddStroke adds a stroked Path.
|
||||
func (p *Path) AddStroke(q Path, width Fixed, cap Cap, join Join) {
|
||||
Stroke(p, q, width, cap, join)
|
||||
}
|
||||
|
||||
// Stroke adds the stroked Path q to p.
|
||||
func Stroke(p Adder, q Path, width Fixed, cap Cap, join Join) {
|
||||
if len(q) == 0 {
|
||||
return
|
||||
}
|
||||
if q[0] != 0 {
|
||||
panic("freetype/raster: bad path")
|
||||
}
|
||||
i := 0
|
||||
for j := 3; j < len(q); {
|
||||
switch q[j] {
|
||||
case 0:
|
||||
stroke(p, q[i:j], width, cap, join)
|
||||
i, j = j, j+3
|
||||
case 1:
|
||||
j += 3
|
||||
case 2:
|
||||
j += 5
|
||||
case 3:
|
||||
j += 7
|
||||
}
|
||||
}
|
||||
stroke(p, q[i:len(q)], width, cap, join)
|
||||
}
|
||||
|
||||
// stroke adds the stroked Path q to p, where q consists of exactly one curve.
|
||||
func stroke(p Adder, q Path, width Fixed, cap Cap, join Join) {
|
||||
// TODO(nigeltao): replace this placeholder stroking algorithm. It only
|
||||
// handles linear segments, and it doesn't cap or join but instead only
|
||||
// fattens each segment independently by half the width, and doesn't
|
||||
// correct for overlaps.
|
||||
a := Point{q[1], q[2]}
|
||||
for i := 3; i < len(q); {
|
||||
switch q[i] {
|
||||
case 1:
|
||||
bx, by := q[i+1], q[i+2]
|
||||
delta := Point{bx - a.X, by - a.Y}
|
||||
normal := delta.Norm(width / 2).RotateCCW()
|
||||
start := Point{a.X + normal.X, a.Y + normal.Y}
|
||||
p.Start(start)
|
||||
p.Add1(Point{bx + normal.X, by + normal.Y})
|
||||
p.Add1(Point{bx - normal.X, by - normal.Y})
|
||||
p.Add1(Point{a.X - normal.X, a.Y - normal.Y})
|
||||
p.Add1(start)
|
||||
a = Point{q[i+1], q[i+2]}
|
||||
i += 3
|
||||
case 2:
|
||||
panic("freetype/raster: stroke unimplemented for quadratic segments")
|
||||
case 3:
|
||||
panic("freetype/raster: stroke unimplemented for cubic segments")
|
||||
default:
|
||||
panic("freetype/raster: bad path")
|
||||
}
|
||||
}
|
||||
}
|
||||
|
|
@ -16,42 +16,9 @@
|
|||
package raster
|
||||
|
||||
import (
|
||||
"fmt"
|
||||
"strconv"
|
||||
)
|
||||
|
||||
// A 24.8 fixed point number.
|
||||
type Fixed int32
|
||||
|
||||
// Human-readable format for a 24.8 fixed point number. For example, the
|
||||
// number one-and-a-quarter becomes "1:064".
|
||||
func (x Fixed) String() string {
|
||||
i, f := x/256, x%256
|
||||
if f < 0 {
|
||||
f = -f
|
||||
}
|
||||
return fmt.Sprintf("%d:%03d", int32(i), int32(f))
|
||||
}
|
||||
|
||||
// maxAbs returns the maximum of abs(a) and abs(b).
|
||||
func maxAbs(a, b Fixed) Fixed {
|
||||
if a < 0 {
|
||||
a = -a
|
||||
}
|
||||
if b < 0 {
|
||||
b = -b
|
||||
}
|
||||
if a < b {
|
||||
return b
|
||||
}
|
||||
return a
|
||||
}
|
||||
|
||||
// Two-dimensional point, in 24.8 fixed point format.
|
||||
type Point struct {
|
||||
X, Y Fixed
|
||||
}
|
||||
|
||||
// A cell is part of a linked list (for a given yi co-ordinate) of accumulated
|
||||
// area/coverage for the pixel at (xi, yi).
|
||||
type cell struct {
|
||||
|
|
@ -453,6 +420,33 @@ func (r *Rasterizer) Add3(b, c, d Point) {
|
|||
}
|
||||
}
|
||||
|
||||
// AddPath adds the given Path.
|
||||
func (r *Rasterizer) AddPath(p Path) {
|
||||
for i := 0; i < len(p); {
|
||||
switch p[i] {
|
||||
case 0:
|
||||
r.Start(Point{p[i+1], p[i+2]})
|
||||
i += 3
|
||||
case 1:
|
||||
r.Add1(Point{p[i+1], p[i+2]})
|
||||
i += 3
|
||||
case 2:
|
||||
r.Add2(Point{p[i+1], p[i+2]}, Point{p[i+3], p[i+4]})
|
||||
i += 5
|
||||
case 3:
|
||||
r.Add3(Point{p[i+1], p[i+2]}, Point{p[i+3], p[i+4]}, Point{p[i+5], p[i+6]})
|
||||
i += 7
|
||||
default:
|
||||
panic("freetype/raster: bad path")
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
// AddStroke adds a stroked Path.
|
||||
func (r *Rasterizer) AddStroke(q Path, width Fixed, cap Cap, join Join) {
|
||||
Stroke(r, q, width, cap, join)
|
||||
}
|
||||
|
||||
// Converts an area value to a uint32 alpha value. A completely filled pixel
|
||||
// corresponds to an area of 256*256*2, and an alpha of 1<<32-1. The
|
||||
// conversion of area values greater than this depends on the winding rule:
|
||||
|
|
@ -533,7 +527,7 @@ func (r *Rasterizer) Rasterize(p Painter) {
|
|||
p.Paint(r.spanBuf[0:s], true)
|
||||
}
|
||||
|
||||
// Clear cancels any previous calls to r.Start or r.AddN.
|
||||
// Clear cancels any previous calls to r.Start or r.AddXxx.
|
||||
func (r *Rasterizer) Clear() {
|
||||
r.a = Point{0, 0}
|
||||
r.xi = 0
|
||||
|
|
|
|||
Loading…
Reference in New Issue
Block a user