So here it is. Or rather, on sourceforge, see link on page 1.
This time, I need to talk about the technical details, as you need this knowledge to find the best parameters for your game. The latest patch uses a dual approach:
A static threshold is used to find areas of nearly-equal colours. The static threshold ranges from 0-255 and has the exact same meaning as before.
After applying the static threshold, the 4 input pixels involved in each output pixel are analyzed and the maximum and minimum difference is calculated. Then an average value of these two is calculated, which is user-configurable from 100% maximum/0% minimum to 0% maximum/100% minimum. This adaptive threshold ranges from 0-100, 75 means the adaptive threshold value is 75%max + 25%min.
Thus, there are 4 keys to tweak these settings: Ctrl+Alt+F3/F4 decrease/increase the static threshold. Ctrl+Alt+F5/F6 decrease/increase the adaptive ratio.
The default value is 0/75 (no static threshold, 75%max adaptive threshold), which is very good for simple cases. But when you have games like Master of Magic, with rendered&anti-aliased graphics but also many sharp edges, you need both settings. Likewise for X-Com, which has many (supposedly) smooth areas, yet also some edges which differ by only a small colour amount. Final example is Ultima 4 (+VGA patch), which has mostly easy scalable line graphics, but a few very noticeable line steps, the avatar even has some anti-aliasing.
Each one has different properties. The key to success is to find the optimum usage of static vs. adaptive threshold. Using this procedure, you get the optimum values for your game in 15 minutes at most:
Start the game, play it a bit with default settings. Look for edges or line steps you don't like. Also watch for edges it gets right. Try to get the working and non-working places on screen simultaneously, or at least near each other.
Now try to increase the dynamic threshold. Doesn't work? Fine, turn it down to 0. Increase the static threshold until it gets some edges (hopefully some of the previously non-working ones). As soon as that happens, turn the dynamic threshold up again, see if it gets the rest of the edges as well. Nothing happens, or it gets too much? Turn down the static threshold until the wrong edges are right again. Turn up the dynamic threshold until the missing edges get recognized. Repeat 5-10 times until everything looks right.
No success? Then try the opposite direction: dynamic threshold 100, turn up static until all edges are recognized. If wrong edges remain, lower dynamic until the wrong edges disappear. Repeat until everything works okay.
So you think you are done? Move the mouse. See if the mouse pointer is interrupted, especially in busy areas. If it is, increase the adaptive threshold (if using the first approach) or the static one (if using the second approach). Keep the correct edges always correct, and try to get as much mouse pointer correctness as possible - this is simply not possible at all times, but try to get the best possible value.
Peek at the console to see which values you have set last and set them in dosbox.conf. Complicated, but worth the effort, IMHO.
Feel free to post your values here, I'd like to see some more. If it works well enough, I may feel inclined to do Hq3x next. Funny how opinions can change - Hq2x is so good, now the blurriness of fullscreen-on-a-LCD annoys me 😀
P.S.: My prime success case is X-Com: I use static 16, adaptive 54, which works 98% perfect. (The last part I'd love to see would be the pattern on ufo floor tiles, but I guess that's impossible to get while having smoothened outer ufo walls.)
Masters of Magic was also hard to get: I use static 54, adaptive 100, but I'm not entirely convinced by that yet - gets everything, but too blurry in some parts.