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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.

Contrast

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

The safe content of the screen may not be updated properly, if the unsafe content causes an overflow in the graphics processing unit (GPU) and prevents rendering the safe content.

Note: It is important, that the safe layout is tested with a certified graphics processing unit.

Refreshing of Overlapping Elements

From Qt Safe Renderer 1.1 onwards, safety-critical UI elements can overlap with each other. When the topmost UI element no longer overlaps with some other element, the bottom UI element is not automatically refreshed. Instead, refreshing requires a manual event.

Visibility After Scaling

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

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