in GUI Development by

I wonder that has Filled Path support alphablended or not ? If not, Is there any way to make the same function.

Best regards

1 Answer

+1 vote


the contents displayed with Filled Path are of course alphablended with the contents found in the background. Concrete, if you specify a semi-transparent color, the Filled Path will appear semi-transparent. Please see the section Specify the color of the filled path.

Best regards

Paul Banach

Hi Paul,

How about alphablended = falsed for Filled Path. Or Alphablended = false for  "TrackLeftColorForcused" in a knob widget.

If they are not supported. Could you please share me some method to set alpha color for specific pixel (those pixels are followed a path like as arc, pie...)in a bitmap image in the runtime.

Thank you

Hello Kxfeash,

Filled Path and Stroked Path views are working implicitly with alphablending. Since Rotary Knob uses these views to display the track, disabling alphablending in such case is also not available. Disabling alphablending would result in the entire shape of the Filled Path overwriting the background contents. This is probably not what you expect.

What you try to achieve is unfortunately not possible. I suppose you want to implement a kind of mask operation with the mask changing dynamically at the runtime. Even if you would disable the alphablending, the pixel resulting from the path will overwrite the pixel in the background. In other words the Filled Path will replace the alpha AND the color information resulting from the bitmap.

I don't know your exact application case. However, if the affected bitmap is displayed directly in the background of the application and the remaining background is filled with solid color you can do following:

1. Display the bitmap.

2. In front of the Bitmap display a Filled Path view.

3. The content shown in the Filled Path view has to be an inverse of what you want to see of the bitmap.

4. The color of the Filled Path ha to correspond to the color of the background.

With this trick you overwrite the parts of the bitmap which should become invisible. This however will not do what you probably expect to do with the Rotary Knob. To achieve this, we would need to extend the Graphics Engine by bitmap operations with an additional source bitmap as mask.

I hope you can workaround your GUI design to avoid the usage of masked bitmaps.

Best regards

Paul Banach
Thank you for responding quickly.

Unfortunaterly, my backgound is not solid color. It's gradient one. It's seem that Filled Path support solid color only.

With Filled Path, yes, I would like to overwrite a part of undelying objects by the Filled Path (with Buffered = True trick).

Is there any ways to customize the TraceLeft of Knob or Gauge by a Resourse::bitmap instead of color ?. ( You guys done it well with Value Bar ).

Best Regards,


Hi Kxfeash,

in fact Filled Path support gradients, but I'm not sure whether this can help you further. The following figure demonstrates few examples of Filled Path being shown with gradients:

In turn, Value Bar is simple, it is rectangular. It displays an area of a bitmap by clipping it with a simple rectangle. From technical point of view it is still a simple copy operation of a rectangular area between the source bitmap and the display. With Gauge and Rotary Knob the area to clip is an arc so the simple rectangular copy operation can't be applied here anymore.

Best regards

Paul Banach

I've tried to create gradient path, but it quite hard to reach my target (same color with background).

Thank you very much for your support :)


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