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pulling_texture.html
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<!-- vim: sw=4 ts=4 expandtab smartindent ft=javascript
-->
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<title>WebGL Demo</title>
<style> document, body { margin: 0px; padding: 0px; overflow: hidden; } </style>
</head>
<body>
<canvas id="glcanvas"></canvas>
<script>
const canvas = document.getElementById('glcanvas');
const gl = canvas.getContext('webgl2', {antialias: true});
if (!gl) { alert('Failed to initialize WebGL'); }
(window.onresize = () => {
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
/* account for e.g. high-retina macbook screens */
if (window.devicePixelRatio > 1) {
canvas.style.width = `${canvas.width}px`;
canvas.style.height = `${canvas.height}px`;
canvas.width *= window.devicePixelRatio;
canvas.height *= window.devicePixelRatio;
}
gl.viewport(
0,
0,
canvas.width,
canvas.height
);
})();
const geo_vbuf_pos = gl.createBuffer();
const geo_vbuf_color = gl.createBuffer();
const geo_ibuf = gl.createBuffer();
let shaders;
/* compile shaders */
{
const vs_geo = `#version 300 es
in vec3 a_pos;
in vec4 a_color;
out vec4 v_color;
uniform sampler2D u_tex_position;
void main() {
vec4 position;
{
ivec2 texel_coord = ivec2(gl_InstanceID % 4, gl_InstanceID / 4);
position = texelFetch(u_tex_position, texel_coord, 0);
}
gl_Position = vec4(position.xyz + a_pos, 1);
v_color = a_color;
}`;
const fs_geo = `#version 300 es
precision mediump float;
in vec4 v_color;
out vec4 color;
void main() {
color = v_color;
}`;
function createProgram(gl, vertexSource, fragmentSource) {
function createShader(gl, type, source) {
const shader = gl.createShader(type);
gl.shaderSource(shader, source);
gl.compileShader(shader);
if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
throw new Error(gl.getShaderInfoLog(shader));
}
return shader;
}
const program = gl.createProgram();
const vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexSource);
const fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentSource);
gl.attachShader(program, vertexShader);
gl.attachShader(program, fragmentShader);
gl.linkProgram(program);
if (!gl.getProgramParameter(program, gl.LINK_STATUS)) {
throw new Error(gl.getProgramInfoLog(program));
}
const wrapper = {program};
const numAttributes = gl.getProgramParameter(program, gl.ACTIVE_ATTRIBUTES);
for (let i = 0; i < numAttributes; i++) {
const attribute = gl.getActiveAttrib(program, i);
wrapper[attribute.name] = gl.getAttribLocation(program, attribute.name);
}
const numUniforms = gl.getProgramParameter(program, gl.ACTIVE_UNIFORMS);
for (let i = 0; i < numUniforms; i++) {
const uniform = gl.getActiveUniform(program, i);
wrapper[uniform.name] = gl.getUniformLocation(program, uniform.name);
}
return wrapper;
}
shaders = {
geo: createProgram(gl, vs_geo, fs_geo)
}
}
/* generate/upload geometry */
let idx_count;
{
const geo_idx = [];
const geo_pos = [];
const geo_color = [];
/* generate geometry */
{
geo_color.push(
255, 0, 0, 255,
0, 255, 0, 255,
0, 0, 255, 255
);
const vbuf_i = geo_pos.length / 3;
geo_pos.push( 0.05, -0.1, 0);
geo_pos.push(-0.05, -0.1, 0);
geo_pos.push( 0.00, 0.1, 0);
geo_idx.push(0, 1, 2);
}
idx_count = geo_idx.length;
/* upload geometry */
{
gl.enableVertexAttribArray(shaders.geo.a_pos);
gl.bindBuffer(gl.ARRAY_BUFFER, geo_vbuf_pos);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(geo_pos), gl.STATIC_DRAW);
gl.enableVertexAttribArray(shaders.geo.a_color);
gl.bindBuffer(gl.ARRAY_BUFFER, geo_vbuf_color);
gl.bufferData(gl.ARRAY_BUFFER, new Uint8Array(geo_color), gl.STATIC_DRAW);
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, geo_ibuf);
gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array(geo_idx), gl.STATIC_DRAW);
}
}
let tex_positions = gl.createTexture();
{
const data = new Float32Array([
-0.1, 0.0, 0.0, 1.0,
0.1, 0.0, 0.0, 1.0,
0.0, 0.1, 0.0, 1.0,
0.0,-0.1, 0.0, 1.0,
-0.4, 0.0, 0.0, 1.0,
0.4, 0.0, 0.0, 1.0,
0.0, 0.4, 0.0, 1.0,
0.0,-0.4, 0.0, 1.0,
-0.8, 0.0, 0.0, 1.0,
0.8, 0.0, 0.0, 1.0,
0.0, 0.8, 0.0, 1.0,
0.0,-0.8, 0.0, 1.0,
-1.2, 0.0, 0.0, 1.0,
1.2, 0.0, 0.0, 1.0,
0.0, 1.2, 0.0, 1.0,
0.0,-1.2, 0.0, 1.0,
]);
gl.bindTexture(gl.TEXTURE_2D, tex_positions);
gl.texImage2D(
gl.TEXTURE_2D,
0, /* mip level */
gl.RGBA32F, /* format */
4, /* width */
4, /* height */
0, /* border */
gl.RGBA, /* format */
gl.FLOAT, /* type */
data,
);
// we don't need any filtering
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
}
requestAnimationFrame(function frame(timestamp) {
requestAnimationFrame(frame);
{
/* set up premultiplied alpha */
gl.blendFunc(gl.ONE, gl.ONE_MINUS_SRC_ALPHA);
gl.enable(gl.BLEND);
gl.enable(gl.DEPTH_TEST);
gl.depthFunc(gl.LEQUAL);
/* clear all */
gl.clearColor(0, 0, 0, 1);
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
/* geo pass */
{
gl.useProgram(shaders.geo.program);
/* bind geometry */
{
gl.bindBuffer(gl.ARRAY_BUFFER, geo_vbuf_pos);
gl.vertexAttribPointer(shaders.geo.a_pos, 3, gl.FLOAT, false, 0, 0);
gl.bindBuffer(gl.ARRAY_BUFFER, geo_vbuf_color);
gl.vertexAttribPointer(shaders.geo.a_color, 4, gl.UNSIGNED_BYTE, true, 0, 0);
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, geo_ibuf);
}
gl.drawElementsInstanced(gl.TRIANGLES, idx_count, gl.UNSIGNED_SHORT, 0, 16);
}
}
})
</script>
</body>
</html>