Difference between Linux and Windows canvas resp. GradientFill?
lazarus / 39-Graphics

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Fish · 2020-05-12 15:55

Hi,

I wrote my own procedure to add, among other things, a gradient to
whatever components which very simplified looks like this:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
PaintGradient(ACanvas: TCanvas);begin  ACanvas.GradientFill(Rect(0, 0,
ACanvas.Width, ACanvas.Height), clRed, clBlue, gdVertical);end;

This works under Linux without any problems. Under Windows it doesn't.
So I made some tests with TPanels and their onPaint events. Under
Linux it makes no difference wether you pass Rect(0, 0, Panel.Width,
Panel.Height) or  Rect(0, 0, Panel.Canvas.Width, Panel.Canvas.Height)
to GradientFill, whereas under Windows only the first version is
working correctly. If you increase the height of the panels, you can
see that there definitely is a gradient, but it seems to run over the
size of the form (?).
Since there is no Canvas.Parent I'm running into problems here. Any
ideas how this can be solved?

Screenshots and test-project attached.
Thanks Chris

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Fish · 2020-05-21 15:09

No one? No idea? No hint? No comment?

I worked around the problem by passing height and width as arguments,
which is working as expected.
But it still would be interesting whether this different behavior is
intended or a bug.

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winni · 2020-05-21 15:51

Hi!

Don't rely on the dimensions of the canvas.
It is known to be buggy in Windows.
Pass the width and the height as parameter to your function.
Take the width and height from the component and not
from the component.canvas.

Winni

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Fish · 2020-05-23 07:13

QuoteIt is known to be buggy in Windows.
Ok, thank you for this information.