Made of little things.

// Adapted from av/safe-sand, e27bafa. See THIRD_PARTY.md for provenance.
export function createContext(canvas) {
  const gl = canvas.getContext('webgl2', {
    antialias: true,
    alpha: false,
    depth: true,
    stencil: false,
    premultipliedAlpha: false,
    preserveDrawingBuffer: false,
    powerPreference: 'high-performance',
  });
  if (!gl) throw new Error('WebGL2 is not available on this device.');
  const cbf = gl.getExtension('EXT_color_buffer_float');
  if (!cbf) throw new Error('This GPU cannot render to float textures (EXT_color_buffer_float).');
  const floatBlend = !!gl.getExtension('EXT_float_blend');
  gl.getExtension('EXT_color_buffer_half_float');
  return { gl, floatBlend };
}

function compile(gl, type, src, name) {
  const s = gl.createShader(type);
  gl.shaderSource(s, src);
  gl.compileShader(s);
  if (!gl.getShaderParameter(s, gl.COMPILE_STATUS)) {
    const log = gl.getShaderInfoLog(s);
    const numbered = src.split('\n').map((l, i) => `${i + 1}: ${l}`).join('\n');
    console.error(numbered);
    throw new Error(`Shader ${name} failed: ${log}`);
  }
  return s;
}

export function program(gl, vs, fs, name = 'program') {
  const p = gl.createProgram();
  const vertex = compile(gl, gl.VERTEX_SHADER, vs, name + '.vs');
  const fragment = compile(gl, gl.FRAGMENT_SHADER, fs, name + '.fs');
  gl.attachShader(p, vertex);
  gl.attachShader(p, fragment);
  gl.linkProgram(p);
  gl.deleteShader(vertex); gl.deleteShader(fragment);
  if (!gl.getProgramParameter(p, gl.LINK_STATUS)) {
    throw new Error(`Program ${name} link failed: ${gl.getProgramInfoLog(p)}`);
  }
  const uniforms = {};
  const n = gl.getProgramParameter(p, gl.ACTIVE_UNIFORMS);
  for (let i = 0; i < n; i++) {
    const info = gl.getActiveUniform(p, i);
    const key = info.name.replace(/\[0\]$/, '');
    uniforms[key] = gl.getUniformLocation(p, info.name);
  }
  return { p, u: uniforms, name };
}

export function texture(gl, w, h, internal, format, type, filter, data = null) {
  const t = gl.createTexture();
  gl.bindTexture(gl.TEXTURE_2D, t);
  gl.texImage2D(gl.TEXTURE_2D, 0, internal, w, h, 0, format, type, data);
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, filter);
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, filter);
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
  return t;
}

export function framebuffer(gl, textures) {
  const fb = gl.createFramebuffer();
  gl.bindFramebuffer(gl.FRAMEBUFFER, fb);
  const bufs = textures.map((t, i) => {
    gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0 + i, gl.TEXTURE_2D, t, 0);
    return gl.COLOR_ATTACHMENT0 + i;
  });
  gl.drawBuffers(bufs);
  const status = gl.checkFramebufferStatus(gl.FRAMEBUFFER);
  if (status !== gl.FRAMEBUFFER_COMPLETE) throw new Error('Framebuffer incomplete: 0x' + status.toString(16));
  gl.bindFramebuffer(gl.FRAMEBUFFER, null);
  return fb;
}

export function setUniforms(gl, prog, values) {
  for (const [k, v] of Object.entries(values)) {
    const loc = prog.u[k];
    if (loc === undefined || loc === null) continue;
    if (typeof v === 'number') gl.uniform1f(loc, v);
    else if (v.type === 'i') gl.uniform1i(loc, v.v);
    else if (v.type === 'u') gl.uniform1ui(loc, v.v);
    else if (v.type === 'v4a') gl.uniform4fv(loc, v.v);
    else if (v.length === 2) gl.uniform2fv(loc, v);
    else if (v.length === 3) gl.uniform3fv(loc, v);
    else if (v.length === 4) gl.uniform4fv(loc, v);
  }
}

export function bindTex(gl, prog, name, tex, unit) {
  gl.activeTexture(gl.TEXTURE0 + unit);
  gl.bindTexture(gl.TEXTURE_2D, tex);
  const loc = prog.u[name];
  if (loc) gl.uniform1i(loc, unit);
}