Python GUIs: Understanding QPainter Coordinates in PyQt6 — How the coordinate system works for drawing on canvases in PyQt6

The useful part

I really having trouble understanding the coordinate system used in QPainter. If you've started drawing with QPainter in PyQt6, you might have been surprised the first time you drew a line. That's because QPainter uses a coordinate system where the origin (0, 0) is in the top-left corner of the canvas, not the bottom-left.

How it works

• This catches a lot of people off guard, so in this tutorial we'll walk through exactly how QPainter coordinates work, how to visualize them, and how to convert between screen coordinates and the...
• In most math courses, you learn to plot points on a Cartesian plane where (0, 0) is at the bottom-left.
• QPainter (and most screen-based graphics systems) does things differently: (0, 0) is at the top-left corner of the drawing surface.
• This means that as your y value gets larger, you move down the screen, not up.
• Here's a simple diagram to illustrate: python (0,0) &boxh&boxh&boxh&boxh&boxh&boxh&boxh&boxh&boxh&boxh&boxh&boxh&boxh&boxh&boxhâ–º x increases &boxv &boxv &boxv &boxv â–¼ y increases So when you call...

Details worth keeping

The x-axis increases to the right, and the y-axis increases upward. The x-axis increases to the right (same as math). The y-axis increases downward (opposite of math).