Original C64 Lode Runner Source Code

Aaaaah it's one 21k assembly file (including data in hex format). Step #1 for anyone trying to port this to another platform will be to split it up into smaller files, no doubt.

this is a great remake of the Load Runner follow up, Mad Monks Revenge. it works amazing on a modern macOS!

https://mmr.quarkrobot.com/

Just wanted to note: this is in no way the original source code for the game. It's disassembled and commented source code.

Here is the repository owner explaining the process himself: https://github.com/Piddewitt/C64-Game-Source-Code

Nice work and interesting still, but maybe we can correct the title?

This can't be the original source code.

https://github.com/Piddewitt/Loderunner/blob/main/Lode%20Run...

Original source, I imagine, would be very tersely commented, if only to fit in memory / floppy, and would have very short variable and subroutine names, and lots of mess and commented-out lines from experiments.

This looks like a very lovingly done disassembly.

  Commented source code of the C64 Lode Runner Game - Including the copy protection

I don't think I ever played an actual 'Lode Runner', just Steve Moraff's version (DOS shareware?)

Whatever happened to that guy?

Look at the subroutine `EnemyMoveGetMaxRowBot` starting at line #9353. On #9414 the data row pointer is set to the enemy's current row. On #9441 it checks if the column to the left is a pole. On #9516 it checks if the column to the right is a pole. Now notice that on #9461 the row pointer is moved to the row below so it can check for a walkable tile (brick or ladder). When the right-side check is done after a left-side check the row pointer will be on the wrong row.

Here it is in C (from my own notes)

    SetCurrentRow1(y);
    if (CURROW1[x] != 0) {
        if (x != 0) {
            if (CURROW1[x-1] == 4) {
                TargetY = y;
                if (y >= PlayerY)
                    return y;
            } else {
                SetCurrentRow1(y+1);
                if (CURROW1[x-1] == 1 || CURROW1[x-1] == 2 || CURROW1[x-1] == 3) {
                    TargetY = y;
                    if (y >= PlayerY)
                        return y;
                }
            }
        }
        if (x < 27) {
            if (CURROW1[x+1] == 4) {
                TargetY = y;
                if (y >= PlayerY)
                    return y;
            } else {
                SetCurrentRow1(y+1);
                if (CURROW1[x+1] == 1 || CURROW1[x+1] == 2 || CURROW1[x+1] == 3) {
                    TargetY = y;
                    if (y >= PlayerY)
                        return y;
                }
            }
        }
    }

The bug can be seen on level 29 if you stand on the left set of blocks that has a single gold in it. The enemies will get stuck on the second ladder which has a pole on the right side.

The Apple II, Atari 8-bit, Commodore 64, and naturally the VIC-20 versions of the game have this bug since they were all made by Broderbund. But interestingly so does the Hudson Soft NES port. The later Macintosh version, which is otherwise a direct port of the Apple II code, fixed it. The IBM-PC version didn't have this bug because it was rewritten with the memory layout column-ordered instead of row-ordered. But then introduced a similar bug by subtracting when it should be adding.

(edit: I hadn't checked until just now but I'm amused to find that Lode Runner Legacy from 2017 preserved this bug in the classic game mode.)

oh my, they used my favorite solution for the how to draw a circle interview question

I love how well structured these old 8bit asm games always seem to be.

One of my first video games I played. I loved designing my own levels.

I just went to a talk at Portland Retro Game Festival by the dutch guy that made an official Atari Lode Runner port. He said he found a japanese book that had the C source in it and got the enemy AI from that.

This is pretty cool.

For anyone curious, the draw a circle code in Circle.asm appears to use Bresenham's circle drawing algorithm.

https://www.geeksforgeeks.org/c/bresenhams-circle-drawing-al...

The secret is to draw 1 arc of a 45 degree angle and the reflect it (redraw it with different coordinates).