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metaballs.html
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metaballs.html
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<html>
<head>
<style type="text/css">
html, body {margin: 0;}
canvas {width: 100%; height: 100%}
</style>
</head>
<body>
<canvas id="main" width="800" height="450" />
<script language="javascript">
/**
* Part 4 Challenges:
*
* - Eliminate the if statement in the fragment shader using step() and mix()
* - Make the motion of the metaball centers more complex by making
* them attracted to one another
*/
var canvas = document.getElementById("main");
var gl = canvas.getContext('webgl');
var NUM_METABALLS = 20;
var WIDTH = canvas.width;
var HEIGHT = canvas.height;
var NEG_FREQUENCY = 0.3;
var SPEED = 1;
var RADIUS = 100;
var MIN_RADIUS = 50;
/**
* Shaders
*/
// Utility to fail loudly on shader compilation failure
function compileShader(shaderSource, shaderType) {
var shader = gl.createShader(shaderType);
gl.shaderSource(shader, shaderSource);
gl.compileShader(shader);
if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
throw "Shader compile failed with: " + gl.getShaderInfoLog(shader);
}
return shader;
}
var vertexShader = compileShader('\n\
attribute vec2 position;\n\
\n\
void main() {\n\
// position specifies only x and y.\n\
// We set z to be 0.0, and w to be 1.0\n\
gl_Position = vec4(position, 0.0, 1.0);\n\
}\
', gl.VERTEX_SHADER);
var fragmentShader = compileShader('\n\
precision highp float;\n\
uniform vec4 metaballs[' + NUM_METABALLS + '];\n\
const float WIDTH = ' + WIDTH + '.0;\n\
const float HEIGHT = ' + HEIGHT + '.0;\n\
\n\
void main(){\n\
float x = gl_FragCoord.x;\n\
float y = gl_FragCoord.y;\n\
float v = 0.0;\n\
for (int i = 0; i < ' + NUM_METABALLS + '; i++) {\n\
vec4 mb = metaballs[i];\n\
float dx = mb.x - x;\n\
float dy = mb.y - y;\n\
float r = mb.z;\n\
float weight = mb.w;\n\
v += weight*r*r/(dx*dx + dy*dy);\n\
}\n\
if (v > -100000.0) {\n\
gl_FragColor = vec4(x/WIDTH, y/HEIGHT,\n\
0.0, 1.0);\n\
gl_FragColor = vec4(v/10.0, v/20.0, 0, 1.0);\n\
} else {\n\
gl_FragColor = vec4(0.0, 0.0, 0.0, 1.0);\n\
}\n\
}\n\
', gl.FRAGMENT_SHADER);
var program = gl.createProgram();
gl.attachShader(program, vertexShader);
gl.attachShader(program, fragmentShader);
gl.linkProgram(program);
gl.useProgram(program);
/**
* Geometry setup
*/
// Set up 4 vertices, which we'll draw as a rectangle
// via 2 triangles
//
// A---C
// | /|
// | / |
// |/ |
// B---D
//
// We order them like so, so that when we draw with
// gl.TRIANGLE_STRIP, we draw triangle ABC and BCD.
var vertexData = new Float32Array([
-1.0, 1.0, // top left
-1.0, -1.0, // bottom left
1.0, 1.0, // top right
1.0, -1.0, // bottom right
]);
var vertexDataBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, vertexDataBuffer);
gl.bufferData(gl.ARRAY_BUFFER, vertexData, gl.STATIC_DRAW);
/**
* Attribute setup
*/
// Utility to complain loudly if we fail to find the attribute
function getAttribLocation(program, name) {
var attributeLocation = gl.getAttribLocation(program, name);
if (attributeLocation === -1) {
throw 'Can not find attribute ' + name + '.';
}
return attributeLocation;
}
// To make the geometry information available in the shader as attributes, we
// need to tell WebGL what the layout of our data in the vertex buffer is.
var positionHandle = getAttribLocation(program, 'position');
gl.enableVertexAttribArray(positionHandle);
gl.vertexAttribPointer(positionHandle,
2, // position is a vec2
gl.FLOAT, // each component is a float
gl.FALSE, // don't normalize values
2 * 4, // two 4 byte float components per vertex
0 // offset into each span of vertex data
);
/**
* Simulation setup
*/
var metaballs = [];
for (var i = 0; i < NUM_METABALLS; i++) {
var radius = Math.random() * RADIUS + MIN_RADIUS;
var weight = 1;
if (Math.random() < NEG_FREQUENCY) {
weight = -1;
}
metaballs.push({
x: Math.random() * (WIDTH - 2 * radius) + radius,
y: Math.random() * (HEIGHT - 2 * radius) + radius,
vx: Math.random() * SPEED - SPEED/2.0,
vy: Math.random() * SPEED - SPEED/2.0,
r: radius,
weight: weight
});
}
/**
* Uniform setup
*/
// Utility to complain loudly if we fail to find the uniform
function getUniformLocation(program, name) {
var uniformLocation = gl.getUniformLocation(program, name);
if (uniformLocation === -1) {
throw 'Can not find uniform ' + name + '.';
}
return uniformLocation;
}
var metaballsHandle = getUniformLocation(program, 'metaballs');
/**
* Simulation step, data transfer, and drawing
*/
var step = function() {
// Update positions and speeds
for (var i = 0; i < NUM_METABALLS; i++) {
var mb = metaballs[i];
mb.x += mb.vx;
if (mb.x - mb.r < 0) {
mb.x = mb.r + 1;
mb.vx = Math.abs(mb.vx);
} else if (mb.x + mb.r > WIDTH) {
mb.x = WIDTH - mb.r;
mb.vx = -Math.abs(mb.vx);
}
mb.y += mb.vy;
if (mb.y - mb.r < 0) {
mb.y = mb.r + 1;
mb.vy = Math.abs(mb.vy);
} else if (mb.y + mb.r > HEIGHT) {
mb.y = HEIGHT - mb.r;
mb.vy = -Math.abs(mb.vy);
}
}
// To send the data to the GPU, we first need to
// flatten our data into a single array.
var dataToSendToGPU = new Float32Array(4 * NUM_METABALLS);
for (var i = 0; i < NUM_METABALLS; i++) {
var baseIndex = 4 * i;
var mb = metaballs[i];
dataToSendToGPU[baseIndex + 0] = mb.x;
dataToSendToGPU[baseIndex + 1] = mb.y;
dataToSendToGPU[baseIndex + 2] = mb.r;
dataToSendToGPU[baseIndex + 3] = mb.weight;
}
gl.uniform4fv(metaballsHandle, dataToSendToGPU);
gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4);
requestAnimationFrame(step);
};
step();
</script>
</body>
</html>