Drawing in Canvas off by a point

ptotushek

Summary

When drawing a round rectangle (or rectangle, etc.) in a canvas using (0, 0, g.width, g.height) half of the line width is cut off on all sides. Also on a round rectangle, the corners are funky using these parameters.

Operating System

I only tested with MacOS (M4 Pro)

Steps To Reproduce

if you use g.DrawRoundRectangle (0, 0, g.width, g.height, 8) you should see this issue. If you use g.DrawRoundRectangle (1, 1, g.width - 2, g.height - 2) then it looks correct.

Objo Studio Version

version 26.6.4

Expected Result

See second screenshot

Actual Result

See first screenshot

Screenshots, Logs, Or Sample Project

Syntec

I am not 100% but is this not the expected behaviour? a pen's width is centred on its path. If that path is at the boundary of a canvas 50% of the line would be cut off. It might be possible to implement a pen location (outside - middle - inside) for closed boundaries but open curves would have no concept of outside - middle - inside so it may not be practical to implement.

ptotushek

Thanks for your insight Syntec. You are right about it being centered. I changed the pen width to 4 (using 0, 0, g.width, g.height) and now the lines around the outside are 2 pixels deep with corners that are still smeared. This would be a little different than Xojo as (0, 0) is the start of the pen width instead of the middle and Xojo works as my original expected results above.

Syntec

That is really interesting, it seems like Xojo assumed most users would want the full pen width inside closed boundaries and honestly that is the most likely intended use case and prevents the user from having to do math but doesn't reflect the real world function of a pen. I might play around with Xojo and bit to see their pen logic, I don't recall any options to change pen behaviour. I assume when drawing open curves the pen is centred otherwise it would just be a mess trying to determine what is inside and outside.

Maybe Garry could implement a pen.location property with outside - middle (or centred) - inside for closed boundary drawing. If you are familiar with the stroke function in photoshop it is basically the same principal/options.

Garry

Fixed in the next release so it behaves how you think it should @ptotushek:

https://feedback.objo.dev/bug/498