Hmm, I’m not sure if this is actually much of an improvement. But here it is.
There’s an arc function and an Arc class. Parameters are centre, xaxis (can be vec2 or number), yaxis (ditto), start angle (radians), delta angle (radians).
-- Arc path drawing
Arc = class()
local __makeArc = function(nsteps)
-- nsteps doesn't make a huge difference in the range 50,300
nsteps = nsteps or 50
local m = mesh()
m.shader = shader([[
//
// A basic vertex shader
//
//This is the current model * view * projection matrix
// Codea sets it automatically
uniform mat4 modelViewProjection;
uniform lowp vec4 scolour;
uniform lowp vec4 ecolour;
lowp vec4 mcolour = ecolour - scolour;
//This is the current mesh vertex position, color and tex coord
// Set automatically
attribute vec4 position;
attribute vec4 color;
attribute vec2 texCoord;
varying highp vec2 vTexCoord;
varying lowp vec4 vColour;
varying highp float vWidth;
varying highp float vCore;
uniform float width;
uniform float taper;
uniform float blur;
uniform float cap;
uniform float scap;
uniform float ecap;
float swidth = width + blur;
float ewidth = taper*width - width;
float ecapsw = clamp(cap,0.,1.)*ecap;
float scapsw = clamp(cap,0.,1.)*scap;
uniform vec2 centre;
uniform vec2 xaxis;
uniform vec2 yaxis;
uniform float startAngle;
uniform float deltaAngle;
void main()
{
highp float t = clamp(position.y,0.,1.);
vCore = t;
highp float w = smoothstep(0.,1.,t);
vWidth = w*ewidth + swidth;
highp vec2 bpos = centre + cos(t*deltaAngle + startAngle) * xaxis + sin(t*deltaAngle + startAngle) * yaxis;
highp vec2 bdir = -sin(t*deltaAngle + startAngle) * xaxis + cos(t*deltaAngle + startAngle) * yaxis;
bdir = vec2(bdir.y,-bdir.x);
bdir = vWidth*normalize(bdir);
bpos = bpos + position.x*bdir;
highp vec4 bzpos = vec4(bpos.x,bpos.y,0.,1.);
bzpos.xy += (ecapsw*max(position.y-1.,0.)
+scapsw*min(position.y,0.))*vec2(-bdir.y,bdir.x);
highp float s = clamp(position.y,
scapsw*position.y,1.+ecapsw*(position.y-1.));
vTexCoord = vec2(texCoord.x,s);
vColour = t*mcolour + scolour;
//Multiply the vertex position by our combined transform
gl_Position = modelViewProjection * bzpos;
}
]],[[
//
// A basic fragment shader
//
uniform highp float blur;
uniform highp float cap;
varying highp vec2 vTexCoord;
varying highp float vWidth;
varying lowp vec4 vColour;
varying highp float vCore;
void main()
{
lowp vec4 col = vColour;
highp float edge = blur/(vWidth+blur);
col.a = mix( 0., col.a,
(2.-cap)*smoothstep( 0., edge,
min(vTexCoord.x,1. - vTexCoord.x) )
* smoothstep( 0., edge,
min(1.5-vTexCoord.y, .5+vTexCoord.y) )
+ (cap - 1.)*smoothstep( 0., edge,
.5-length(vTexCoord - vec2(.5,vCore)))
);
gl_FragColor = col;
}
]])
for n=1,nsteps do
m:addRect(0,(n-.5)/nsteps,1,1/nsteps)
end
m:addRect(0,1.25,1,.5)
m:addRect(0,-.25,1,.5)
return m
end
local m = __makeArc()
m.shader.blur = 2
m.shader.cap = 2
m.shader.scap = 1
m.shader.ecap = 1
-- centre, xaxis, yaxis, startAngle, deltaAngle, taper
function arc(a,b,c,d,e,f)
if type(a) == "table" then
f = b
a,b,c,d,e = unpack(a)
end
if type(b) ~= "userdata" then
b = b*vec2(1,0)
end
if type(c) ~= "userdata" then
c = c*vec2(0,1)
end
--m.shader.blur = 15
m.shader.taper = f or 1
m.shader.width = strokeWidth()
m.shader.scolour = color(stroke())
m.shader.ecolour = color(stroke())
m.shader.cap = (lineCapMode()-1)%3
m.shader.centre = a
m.shader.xaxis = b
m.shader.yaxis = c
m.shader.startAngle = d
m.shader.deltaAngle = e
m:draw()
end
function Arc:init(...)
self:setParams(...)
end
function Arc:clone()
return Arc(self.params)
end
function Arc:makeDrawable(t)
t = t or {}
local nsteps = t.steps or self.steps
local m = __makeArc(nsteps)
m.shader.taper = t.taper or self.taper or 1
m.shader.blur = t.blur or self.blur or 2
m.shader.cap = t.cap or self.cap or (lineCapMode()-1)%3
m.shader.scap = t.scap or self.scap or 1
m.shader.ecap = t.ecap or self.ecap or 1
m.shader.width = t.width or self.width or strokeWidth()
m.shader.scolour = t.scolour or self.scolour or t.colour or color(stroke())
m.shader.ecolour = t.ecolour or self.ecolour or t.colour or color(stroke())
local a,b,c,d,e = unpack(self.params)
m.shader.centre = a
m.shader.xaxis = b
m.shader.yaxis = c
m.shader.startAngle = d
m.shader.deltaAngle = e
self.curve = m
self.draw = function(self) self.curve:draw() end
end
function Arc:draw(t)
self:makeDrawable(t)
self.curve:draw()
end
function Arc:setParams(a,b,c,d,e)
if type(a) == "table" then
a,b,c,d,e = unpack(a)
end
if type(b) ~= "userdata" then
b = b*vec2(1,0)
end
if type(c) ~= "userdata" then
c = c*vec2(0,1)
end
self.params = {a,b,c,d,e}
if self.curve then
self.curve.shader.centre = a
self.curve.shader.xaxis = b
self.curve.shader.yaxis = c
self.curve.shader.startAngle = d
self.curve.shader.deltaAngle = e
end
end
function Arc:setStyle(t)
self.scolour = t.scolour or t.colour or self.scolour
self.ecolour = t.ecolour or t.colour or self.ecolour
self.width = t.width or self.width
self.taper = t.taper or self.taper
self.blur = t.blur or self.blur
self.cap = t.cap or self.cap
self.scap = t.scap or self.scap
self.ecap = t.ecap or self.ecap
if not self.curve then
return
end
t = t or {}
if t.colour then
self.curve.shader.scolour = t.colour
self.curve.shader.ecolour = t.colour
end
if t.scolour then
self.curve.shader.scolour = t.scolour
end
if t.ecolour then
self.curve.shader.ecolour = t.ecolour
end
if t.width then
self.curve.shader.width = t.width
end
if t.taper then
self.curve.shader.taper = t.taper
end
if t.blur then
self.curve.shader.blur = t.blur
end
if t.cap then
self.curve.shader.cap = t.cap
end
if t.scap then
self.curve.shader.scap = t.scap
end
if t.ecap then
self.curve.shader.ecap = t.ecap
end
end
function Arc:point(t)
local a,b,c,d,e = unpack(self.params)
return a + math.cos(t*e + d)*b + math.sin(t*e + d)*c
end
function Arc:tangent(t)
local a,b,c,d,e = unpack(self.params)
return -math.sin(t*e + d)*b + math.cos(t*e + d)*c
end
function Arc:normal(t)
return self:tangent(t):rotate90()
end
function Arc:unitNormal(t)
local pt = self:normal(t)
local l = pt:len()
if l == 0 then
return vec2(0,0)
else
return pt/l
end
end
function Arc:unitTangent(t)
local pt = self:tangent(t)
local l = pt:len()
if l == 0 then
return vec2(0,0)
else
return pt/l
end
end
