• Rect函数中的clamp(uv, -size/2.0, size/2.0))是我们决定点是否在矩形区域的技巧
• 函数Rotate(vec2 uv,float angle)将坐标点旋转到水平或垂直位置方便我们确定Rect和Line参数进行对比
• Blend函数mix(shapeColor, backColor, smoothstep(0.0, 0.005, shape))是常用的混合mix和smoothstep达到更好处理边缘平滑效果GLSL常用技巧

#ifdef GL_ES
precision mediump float;
#endif

uniform float time;
uniform vec2 resolution;

float pi = 3.1415926;
float tau = pi * 2.0;

vec2 Rotate(vec2 uv,float angle);

float Circle(vec2 uv,float r);
float Rect(vec2 uv,vec2 size,float r);
float Line(vec2 uv,vec2 start,vec2 end,float r);
float Merge(float a,float b);
float Outline(float a,float r);

vec3 Blend(vec3 backColor, vec3 shapeColor, float shape);

float SecStep(float x);

void main( void )
{
vec2 res = resolution / resolution.y;
vec2 uv = ( gl_FragCoord.xy / resolution.y );
uv -= res / 2.0;

float secAng = (SecStep(time) / 60.0) * tau;
float minAng = (time / 3600.0) * tau;
float hourAng = (time / 43200.0) * tau;

float clockFace = Circle(uv, 0.45);
float clockTrim = Outline(clockFace, 0.01);

vec2 secDomain = Rotate(uv, secAng);
float clockSec = Line(secDomain, vec2(0.0, -0.15), vec2(0.0, 0.35), 0.001);
clockSec = Merge(clockSec, Circle(uv, 0.01));
clockSec = Merge(clockSec, Rect(secDomain - vec2(0.0, -0.08), vec2(0.012, 0.07), 0.0));

float clockMin = Line(Rotate(uv, minAng), vec2(0.0,-0.08), vec2(0.0, 0.35), 0.005);
float clockHour = Line(Rotate(uv, hourAng), vec2(0.0,-0.05), vec2(0.0,0.3), 0.007);
clockHour = Merge(clockHour, Circle(uv, 0.02));

float tickMarks = 1.0;
vec2 tickDomain = uv;
for(int i = 0;i < 60;i++)
{
tickDomain = Rotate(tickDomain, tau / 60.0);
vec2 size = (mod(float(i + 1), 5.0) == 0.0) ? vec2(0.08, 0.01) : vec2(0.04, 0.002);
tickMarks = Merge(tickMarks, Rect(tickDomain - vec2(0.38, 0.0), size, 0.0));
}

vec3 faceColor = mix(vec3(1.0, 1.0, 0.0), vec3(1.0, 1.0, 1.0), uv.x+0.5);
vec3 trimColor = mix(vec3(0.0, 1.0, 0.0), vec3(0.0, 0.0, 1.0), uv.y + 0.5);
vec3 secColor = vec3(1.0, 0.0, 0.0);
vec3 handColor = vec3(0.0, 0.0, 0.0);

vec3 color = mix(vec3(1.0, 0.0, 0.0), vec3(1.0, 1.0, 1.0), uv.y+0.5);
color = Blend(color, faceColor, clockFace);
color = Blend(color, trimColor, clockTrim);
color = Blend(color, trimColor, tickMarks);
color = Blend(color, handColor, clockHour);
color = Blend(color, handColor, clockMin);
color = Blend(color, secColor, clockSec);

gl_FragColor = vec4(color, 1.0);
}
float SecStep(float x)
{
float interp = smoothstep(0.80, 1.0, mod(x, 1.0));
return floor(x) + interp + (sin(interp * pi)) ;
}
float Line(vec2 uv,vec2 start,vec2 end,float r)
{
return Rect(uv-(end+start)/2.0, vec2(r, end.y - start.y), r);
}
float Rect(vec2 uv,vec2 size,float r)
{
return length(uv - clamp(uv, -size/2.0, size/2.0)) - r;
}
vec2 Rotate(vec2 uv,float angle)
{
return mat2(cos(angle), sin(angle),-sin(angle), cos(angle)) * uv;
}
float Circle(vec2 uv,float r)
{
return length(uv) - r;
}
float Merge(float a,float b)
{
return min(a, b);
}
float Outline(float a,float r)
{
return abs(a) - r;
}
vec3 Blend(vec3 backColor, vec3 shapeColor, float shape)
{
return mix(shapeColor, backColor, smoothstep(0.0, 0.005, shape));
}

HT for Web中《矢量手册》中自定义绘制的clock例子实现代码如下：

function init() {
dataModel = new ht.DataModel();
graphView = new ht.graph.GraphView(dataModel);
view = graphView.getView();

view.className = 'main';
document.body.appendChild(view);
graphView.invalidate();
}, false);

ht.Default.setCompType('clock-face', function(g, rect, comp, data, view) {
var cx = rect.x + rect.width / 2;
var cy = rect.y + rect.height / 2;
var theta = 0;
var r = Math.min(rect.width, rect.height)/2 * 0.92;

g.strokeStyle = "#137";
for (var i = 0; i < 60; i++) {
g.beginPath();
g.arc(
cx + Math.cos(theta) * r,
cy + Math.sin(theta) * r,
i % 5 === 0 ? 4 : 1,
0, Math.PI * 2, true);
g.closePath();
g.lineWidth = i % 5 === 0 ? 2 : 1;
g.stroke();
theta = theta + (6 * Math.PI / 180);
}
});

ht.Default.setImage('clock', {
width: 500,
height: 500,
comps: [
{
type: 'circle',
relative: true,
rect: [0, 0, 1, 1],
background: 'yellow',
},
{
type: 'clock-face',
relative: true,
rect: [0, 0, 1, 1]
},
{
type: function(g, rect, comp, data, view) {
// get current time
var date = data.a('date');
if(!date){
return;
}

var hours = date.getHours();
var minutes = date.getMinutes();
var seconds = date.getSeconds();
hours = hours > 12 ? hours - 12 : hours;
var hour = hours + minutes / 60;
var minute = minutes + seconds / 60;

// save current context
g.save();

g.beginPath();

// draw numbers
g.font = '36px Arial';
g.fillStyle = '#000';
g.textAlign = 'center';
g.textBaseline = 'middle';
for (var n = 1; n <= 12; n++) {
var theta = (n - 3) * (Math.PI * 2) / 12;
var x = clockRadius * 0.75 * Math.cos(theta);
var y = clockRadius * 0.75 * Math.sin(theta);
g.fillText(n, x, y);
}

// draw hour
g.save();
var theta = (hour - 3) * 2 * Math.PI / 12;
g.rotate(theta);
g.beginPath();
g.moveTo(-15, -5);
g.lineTo(-15, 5);
g.fill();
g.restore();

// draw minute
g.save();
var theta = (minute - 15) * 2 * Math.PI / 60;
g.rotate(theta);
g.beginPath();
g.moveTo(-15, -4);
g.lineTo(-15, 4);
g.fill();
g.restore();

// draw second
g.save();
var theta = (seconds - 15) * 2 * Math.PI / 60;
g.rotate(theta);
g.beginPath();
g.moveTo(-15, -3);
g.lineTo(-15, 3);
g.fillStyle = '#0f0';
g.fill();
g.restore();

g.restore();
}
}
]
});

var node = new ht.Node();
node.setPosition(150, 150);
node.setSize(250, 250);
node.setImage('clock');
node.a('date', new Date());
node.s('image.stretch', 'centerUniform');

graphView.setEditable(true);

setInterval(function(){
node.a('date', new Date());
}, 1000);
}

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