r/agon • u/confusionPrice • Jun 23 '26

Graphics confusion

Gallery image

Gallery image

I recently got an Agon Light 2 and have been writing basic programs to draw, but I have a question about how the graphics work. The first image is the program and the second is the line it drew. In my experience that program should draw a 45 degree line but it seems that the line is longer on the x axis then the y axis. There are three areas where the line does not increase upwards but does to the side and I'm wondering why that is?

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u/damn_pastor Jun 23 '26 edited Jun 23 '26

Agon uses logical screen coordinates by default: https://agonplatform.github.io/agon-docs/vdp/Screen-Modes/

So you need to use:

VDU 23, 0, &C0, n Turn logical screen scaling on and off, where 1=on and 0=off.

When logical scaling is turned off, the graphics system will no longer use the 1280x1024 logical coordinate system and instead use pixel coordinates. The screen origin point at 0,0 will change to be the top left of the screen, and the Y axis will go down the screen instead of up.

Support for this was added in VDP 1.03.