message: fix shader marking issue
diff: // only mark elements with an alpha above the picking threshold
  if (uAlpha >= uPickingAlphaThreshold) {
  - float marker = vMarker * 255.0;
  + float marker = floor(vMarker * 255.0 + 0.5); // rounding required to work on some cards on win
  if (marker > 0.1) {
  if (intMod(marker, 2.0) > 0.1) {
  gl_FragColor.rgb = mix(uHighlightColor, gl_FragColor.rgb, 0.3);
  