Perfect Line Thickness Using TCanvas DrawLine With Delphi XE5 Firemonkey On Android And IOS

If you’re using Delphi XE5 Firemonkey to do any kind of drawing on TCanvas with DrawLine you may have run into this issue. The problem is that when you draw a one pixel line what you end up with doesn’t appear as a one pixel line. I believe this issue exists on both Android and IOS. Roman Yankovsky has a blog post demonstrating the problem and showing the solution. Here is an example of DrawLine where the problem manifests:

Canvas.DrawLine(PointF(50 + I * 25, 0), PointF(50 + I * 25, ClientHeight), 1);

And here is the an example of DrawLine with the extra code that fixes the problem:

Canvas.DrawLine(PointF(50 + I * 25 – (Canvas.Stroke.Thickness / 2), 0),
PointF(50 + I * 25 – (Canvas.Stroke.Thickness / 2), ClientHeight), 1);

Roman has much more comprehensive example code on his blog and even a second method for correcting the problem.

Head over to read the full blog post about correcting DrawLine on TCanvas.