prepare for supporting camera movement via mouse & keyboard

glsl/raymarching.js

    gl.uniform2f(iResolution, canvas.width, canvas.height);
    gl.uniform1f(iGlobalTime, 0.0);
    gl.uniform3f(iMouse, 0.0, 0.0, 0.0);
    
    tt.origin = gl.getUniformLocation(program, 'origin');
    // two triangles
    var positions = new Float32Array([
      }
    });
    
    tt.direction = [0, 0, 1];
    tt.angle = {horizontal: 0.0, vertical: 0.0};
    
    var iDirection = gl.getUniformLocation(program, 'iDirection');
    gl.uniform3f(iDirection, tt.direction[0], tt.direction[1], tt.direction[2]);
    
    var mousePressed = false;
    tt.canvas.addEventListener("mousedown", function(ev) { if (ev.button == 0) { mousePressed = true; }});
    tt.canvas.addEventListener("mouseup", function(ev) { mousePressed = false; });
    
    tt.canvas.addEventListener("mousemove", function(ev) {
      gl.uniform3f(iMouse, ev.clientX, canvas.clientHeight - ev.clientY, 0.0);
      
      if (!mousePressed || !iDirection) {
        return;
      }
      
      tt.angle.horizontal += 0.0001 * (tt.w/2 - ev.clientX);
      tt.angle.vertical += 0.0001 * (tt.h/2 - ev.clientY);
      tt.direction = [Math.cos(tt.angle.vertical) * Math.sin(tt.angle.horizontal),
                      Math.sin(tt.angle.vertical),
                      Math.cos(tt.angle.vertical) * Math.cos(tt.angle.horizontal)];
      
      gl.uniform3f(iDirection, tt.direction[0], tt.direction[1], tt.direction[2]);
      requestAnimationFrame(tt.render);
    });
    
    window.addEventListener('keydown', function(ev) {
      if (document.activeElement != document.body) {
        return;
      }
      
      var origin = tt.gl.getUniform(tt.program, tt.origin);
      
      switch (ev.keyCode) {
        case 87: // W
          origin = [origin[0]+tt.direction[0], origin[1]+tt.direction[1], origin[2]+tt.direction[2]];
          break;
        case 65: // A
          break;
        case 83: // S
          origin = [origin[0]-tt.direction[0], origin[1]-tt.direction[1], origin[2]-tt.direction[2]];
          break;
        case 68: // D
          break;
        default:
          return
      }
      
      gl.uniform3f(tt.origin, origin[0], origin[1], origin[2]);
      requestAnimationFrame(tt.render);
    });
    
    window.onresize = function(ev) {
      tt.w = tt.canvas.width = window.innerWidth;
      tt.h = tt.canvas.height = window.innerHeight;