Thursday, February 21, 2008

Capturing key inputs

Following on what I said yesterday, no emulator would be good enough without the ability to capture key inputs. This is pretty easy and can be quite useful in alot of situations. An exemple of this can be found in the form tutorial_Tetris. (Yes, there is a Tetris game in DAX for those who didn't know!)

The first thing you need to do is add a Tree control to your design and set it's "AutoDeclaration" to Yes. The Tree control allows us to capture the "keyDown" events by overwriting the method with the same name. We can then use the vKey that is passed to this method and do whatever we want when a key is pressed.

boolean keyDown(int vKey, boolean ctrl, boolean shift)
{
        boolean ret;

        ret = super(vKey, ctrl, shift);

        switch (vkey)
        {
                case 49: //1 (1)
                        keyPressed = 2;
                        break;
                case 81: //4 (Q)
                        keyPressed = 5;
                        break;
                case 50: //5 (W)
                        keyPressed = 6;
                        break;
        }
        return ret;
}

So for our emulator, we want to have the emulator focused on the Tree whenever it's not processing information. So after we execute an instruction, we give back the focus to the Tree like so :

void runEmu()
{
        int opcode;
        ;

        opcode = memory[pointer]
        this.execute(opcode);
        pointer++;

        if (emuRunning)
                this.setTimeOut(identifierStr(runEmu),0,false);
        Tree.setFocus();
}

This is just a rough example, but we could call methods from here to execute a certain peice of code or change the emu status (like to pause or play the emulator).

I almost posted today about the importance of making backups of your code but was too annoyed with the fact that I lost a day and a half worth of work :p.... So remember guys, ALWAYS backup your projects, even if automatic backups are suppose to be running every night.

Tuesday, February 19, 2008

Chip8 in DAX 4.0 (continued...)

I know I haven't posted in a while... but I'm bored and this seems like a great time to continue my little adventure with emulation in Microsoft's Dynamics AX 4.0. I will probably not go as in-dept as I originally planned since the Chip8 platform is well-documented already. I'll try to focus on the challenges that the DAX platform brings into emulating a system.

Every emulator consists of a main loop that executes instructions, also known as opcodes. A typical loop in pseudocode would look a little something like this:

while emulor is running
        fetch opcode from memory at pointer's location
        execute opcode
        increase pointer
loop

In DAX this can be something as simple as (The boolean in the while statement can be changed to a variable to allow to start/stop the emulator):

while (true)
{
        opcode = this.memory[pointer];
        this.execute(opcode);
        opcode++;
}

Unfortunatly, if you try to run a loop like this, you will notice that the DAX client seems to hang as it's running an infinite loop. This prevents anything to be updated to the screen (like the Chip8 display area) and prevents any keyboard input to be captured (capturing input will be explained in another blog entry.... which I promise will not be in another month this time!). These issues can be bypassed by doing something like this :

The memory[] array, pointer and emuRunning variable would be declared in the classDeclaration in this exemple.

void runEmu()
{
        int opcode;
        ;

        opcode = memory[pointer]
        this.execute(opcode);
        pointer++;

        if (emuRunning)
                this.setTimeOut(identifierStr(runEmu),0,false);
}

Instead of using a loop, I made use of the setTimeOut method to call the same method over and over again as long as the emulator is running. This leaves enough time for the client to update itself and allow the user to move around any window that would be opened in the client.

That's it for tonight. On a last note, using Threads should work also. I haven't had any free time lately to give it a try but it's kind of like the "Find" feature in DAX. When you search for a string through code, the client will update its result window while it is searching more results.