Tenliner Challenge - #6 Shangri-La

Very impressive!

The powah of BASIC!

Nice demo! It reminds me of great works of "AV forum" of MSX・FAN!

Thank you all for the compliments. It was quite tricky to start coding in basic again. I had quite some looking up to do how stuff worked. Thankfully, the internet is a good place for this. The book from Graham Bland on Hans Otten's site was very helpful.
I was thinking of adding a 5th scroll layer in the last part by using sprites, but simultaneous movement of multiple sprites is just so slow in basic... On the other hand, I was quite surprised by the speed of the copy command. That was faster than I thought. I did not expect to get the hands animation at such a smooth level. Blockfil using the line command is also quite fast, although drawing a single line isn't.

@maggoo, the checkered background in the lastpart, was actually inspired by the sonic replayer from Metal Limit. I always liked big moving things on the screen (which ofcourse you can't do in screen5). Although the replayer did it in a very different way, this is also a nice trick

The really nice thing of basic is actually its limitations. My original thoughts were to use a vdp(24) scroll in the last part. But as basic does not allow you to access the lower part of the screen (line 212 and below) (atleast, I thought - I did not check). One has to come up with different ideas.
Maybe one day I'll rewrite this to assembly and add that fifth sprite layer.

@Manuel, it is basic, c'mon... you can figure it out yourself But I'll try to explain. The last part just comes down to one big logical operator trick, using xor 2 and xor 3. Therefore, you'll need to choose your colors wisely as they are very limited.

The checkered background is color 8 and 10. It appears to scroll by updating the outerline of each block. In this case there is a line update from xpos 0 to xpos 255 by the line command (x,y)-(x2,y2),2,,xor. This will flip color 8 to 10 and 10 to 8.

The white text on screen is color 15 and 7. The operator xor 2 changes these to 13 and 5. As these colors are also set to white, you will not see the change.

The blue vertical bar is drawn over the screen using a line command with xor 3. Here we decide if the bar goes in front or behind the text (or even the background). The table below should clarify it a bit more.

Color xor2 xor3 Comment
0 2 3 Black (border)
1 3 2 Not used
2 2 1 Not used
3 1 0 Not used
4 6 7 vertical bar color
5 7 6 White
6 4 5 vertical bar color
7 5 4 white
8 10 11 Checkered background
9 11 10 Checkered background / vertical bar color
10 8 9 Checkered background
11 9 8 Checkered background / vertical bar color
12 14 15 White / vertical bar color
13 15 14 White
14 12 13 White / vertical bar color
15 13 12 white

By setting color 12 and 14, or 4 and 6 to white (text) or blue(vertical bar), you can determine if the blue vertical bar goes before and behind the text. Updating these color schedules during the program (which I didn't), allows even more cool tricks.

@MRC team
User Nestor Sancho Bejarano was so kind to dive into my program and optimize it. The speed has been greatly increased. Is there a possiblity to replace the current version with the optimized one?

The Shangri-La download has been updated; the disk image now also contains an OPTIM.BAS with the optimized version by Nestor Sancho Bejarano. In accordance with BlueCrystal's wishes, his original entry is the participating entry to the challenge. The optimized version is for your enjoyment.

Beware the powerrrrrrr of MSX-BASIC!