Scaling or rasterizing issue in Autocad 12 and 13 on Windows 3.x

[dodleh]

I have made some tests and it became clear that there is a problem with how PCEM interprets the video drawing routines. For the moment, I have not found other situations were the defect can be reproduced but it happens here.

Configurations tested: 486 AMI WinBIOS or Intel VX 430
RAM: 16MB (although it is not memory specific)
VIDEO RAM: 2MB (although with 1MB the result is the same)
Videocards: S3 Trio 764/864, ATI MACH 64 GX (one round of tests)
Windows 3.11 for Workgroups
Video mode: Driver supported (1.41B5 or standard VGA)
Autocad 12 or 13 for Windows, with or without Accelerated mode activated

Notes: on a typical real system running on VGA mode or accelerated mode with drivers (Cyrus, NeoMedia, unknown S3 card), this does not occur as on PCEM
The screenshot is from Autocad 12 but the same issue occurs in Autocad 13, pointing at a much deeper cause in PCEM due to scaling or rasterizing.

Problem: any text rendering or detailed area (using arcs or a lot of lines) looks distorted. Curves are not rendered accurately and text lacks definition, as if it would be presented at lower resolution. This happens with any Autocad model not just the test one. It does not matter if PCEM videocard's resolution is higher or lower than on a real machine (640x480 or 800x600, if it is in 4 bit color, 8 bit or 16 bit).

[SarahWalker]

Can you provide an example of what that's meant to look like please?

[dodleh]

I highly appreciate your answer. Of course, here is a sample. The biggest difference is on curved lines, with a slightly less obvious text rendering accuracy for smaller character sizes. All these differences between the PCEM image and the real PC one are slightly more noticeable at lower resolutions such as the above shown 800x600 one. Of course, the problem still manifests at 1024x768. However, for the sake of a 1:1 comparison I chose 800x600 as in the initial photo. The problem on curved lines might be due to the bezier curve generation algorithm. However, the hint at how the Autodesk logo in the drawing looks suggests a floating point to integer conversion problem pertaining to precision on the videocard emulation backend but I am not knowledgeable enough in programming to offer more suggestions.