support navigation with cursor keys as well

glsl/raymarching.js

      var origin = tt.gl.getUniform(tt.program, tt.origin);
      
      switch (ev.keyCode) {
        case 38: // Up
        case 87: // W
          origin = [origin[0]+tt.direction[0], origin[1]+tt.direction[1], origin[2]+tt.direction[2]];
          break;
        case 37: // Left
        case 65: // A
          break;
        case 40: // Down
        case 83: // S
          origin = [origin[0]-tt.direction[0], origin[1]-tt.direction[1], origin[2]-tt.direction[2]];
          break;
        case 39: // Right
        case 68: // D
          break;
        default:
          return
      }
      
      ev.preventDefault();
      
      gl.uniform3f(tt.origin, origin[0], origin[1], origin[2]);
      requestAnimationFrame(tt.render);
    });