Features Affecting Visibility of Safety-Critical UI Elements

When you design a layout with safety-critical UI elements, you should be careful with the following Qt Safe Renderer features as they might affect the visibility of the UI elements.

Opacity Value 0 in Animations

From Qt Safe Renderer 1.2 onwards, you can animate safety-critical UI elements. When you use the opacity feature in your animations, you must remember that opacity value 0 makes the safety-critical UI elements invisible in the UI even if a visibility ON event has been sent to the element. See Animations in Safety-Critical UI for more information about animations.

Color of UI Elements

When you select a color of the safety-critical UI element, note that color-blind people or otherwise visually impaired people may not be able to see the UI elements properly.

If the color of the icon is the same as the background color, it is not possible to distinguish the icon from the screen.


From Qt Safe Renderer 2.0 onwards, the Qt Safe Renderer tooling evaluates the contrast between the drawn safety-critical element and the background fill color as follows:

  • Contrast verification is based on the W3C recommendations. For more information, see https://www.w3.org/TR/WCAG/#contrast-minimum.
  • If some issues are detected, you see warning notes. However, in practice, you are responsible for handling the contrast.
  • Note: Contrast depends always on the used display.

Unsafe Content Causing Overflows in GPU

In UI, the non-safe content shall not interfere with the Qt Safe Renderer output. You can ensure this by using separate hardware layers in the display processor.

If you cannot certify the graphics pipeline, you must use the output monitor to validate the rendering output.

Visibility After Scaling

In general, scaling (that is, changing height and width) may affect visibility of UI elements:

  • The quality of the UI element's icon decreases after scaling.
  • The scaled UI element can hide other UI elemnents.
  • The minimized UI element can be invisible.

Available under certain Qt licenses.
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