fix initial rendering

glsl/raymarching.js

    gl.uniform2f(iResolution, w, h);
    render();
  };
  
  render();
  var sidebarEl = document.createElement("div");
  sidebarEl.style = `
  });
  
  addSliders(sidebarEl, sliders);
  
  render();
} catch (e) {
  window.error = e;
  var msg = document.createElement("pre");

glsl/sliders.js

    switch (slider.type) {
      case "float":
        slider.uniform = gl.getUniformLocation(program, slider.name);
        gl.uniform1f(slider.uniform, slider.range[1]);
        
        slider.onChange = function(ev) {
          gl.uniform1f(slider.uniform, parseFloat(ev.target.value));
      case "vec3":
        slider.values = slider.range.map((r) => r[1]);
        slider.uniform = gl.getUniformLocation(program, slider.name);
        if (slider.type == "vec2") {
          gl.uniform2f(slider.uniform, slider.values[0], slider.values[1]);
        } else if (slider.type == "vec3") {
          gl.uniform3f(slider.uniform, slider.values[0], slider.values[1], slider.values[2]);
        } else {
          throw new Error("unknown slider type " + slider.type);
        }
        
        slider.onChange = function(ev, i) {
          slider.values[0] = parseFloat(ev.target.value);