support moving left and right with the keyboard

glsl/raymarching.js

    });
    
    tt.direction = [0, 0, 1];
    tt.right = [-1, 0, 0];
    tt.angle = {horizontal: 0.0, vertical: 0.0};
    
    var iDirection = gl.getUniformLocation(program, 'iDirection');
      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)];
      tt.right = [Math.sin(tt.angle.horizontal - Math.PI/2),
                  0,
                  Math.cos(tt.angle.horizontal - Math.PI/2)];
      
      gl.uniform3f(iDirection, tt.direction[0], tt.direction[1], tt.direction[2]);
          break;
        case 37: // Left
        case 65: // A
          origin = [origin[0]-tt.right[0], origin[1]-tt.right[1], origin[2]-tt.right[2]];
          break;
        case 40: // Down
        case 83: // S
          break;
        case 39: // Right
        case 68: // D
          origin = [origin[0]+tt.right[0], origin[1]+tt.right[1], origin[2]+tt.right[2]];
          break;
        default:
          return