Chip 8 Emulator in Vb.Net - Xtreme Visual Basic Talk

05-08-2010, 12:17 PM

s33k-n-d3str0y s33k-n-d3str0y is offline

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Join Date: May 2010

Posts: 6

Chip 8 Emulator in Vb.Net

hi friends..
i really need your help in this problem..i am trying to create chip 8 emulator in vb.net, i have coded all opcodes so far but the real problem is in drawing sprites as i have really dont have any idea of graphics and how to draw pixels.. please help me i have found this vb 6 code on internet if any one can help me in converting it to vb.net and also improve it and also tell me the logic behind that it will be highly appreciated... but pls do reply quick and keep replying as i have lot of questions but first let done this...

i have these two function that will draw pixels on a picture box..

Code:

Sub DrawSprite()
    v(&HF) = 0
   
    x = v(opcode2) * 4
    y = v(opcode3) * 4
    For j = 0 To opcode4 - 1
        datax = ram(Index + j)
        i = 0
        If datax >= 128 Then
            DrawScreen
            datax = datax - 128
        End If
        i = i + 1
        If datax >= 64 Then
            DrawScreen
            datax = datax - 64
        End If
        i = i + 1
        If datax >= 32 Then
            DrawScreen
            datax = datax - 32
        End If
        i = i + 1
        If datax >= 16 Then
            DrawScreen
            datax = datax - 16
        End If
        i = i + 1
        If datax >= 8 Then
            DrawScreen
            datax = datax - 8
        End If
        i = i + 1
        If datax >= 4 Then
            DrawScreen
            datax = datax - 4
        End If
        i = i + 1
        If datax >= 2 Then
            DrawScreen
            datax = datax - 2
        End If
        i = i + 1
        If datax >= 1 Then
            DrawScreen
            datax = datax - 1
        End If
    Next j

End Sub

Code:

Sub DrawScreen()
        If Picture1.Point(1 + x + (i * 4), y + (j * 4)) = RGB(c1, c2, c3) Then
            v(&HF) = 1
            Picture1.Line (1 + x + (i * 4), y + (j * 4))-(1 + x + (i * 4) + 3, y + (j * 4) + 3), RGB(0, 0, 0), BF
        Else
            Picture1.Line (1 + x + (i * 4), y + (j * 4))-(1 + x + (i * 4) + 3, y + (j * 4) + 3), RGB(c1, c2, c3), BF
        End If
End Sub

the problem Picture.Point and Picture.Line is no longer supported in vb.Net so ho to improve DrawScreen() function??????????

05-08-2010, 06:44 PM

snarfblam

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Posts: 871

If you want to programatically manipulate individual pixels, you probably want to create a Bitmap as a buffer and use LockBits to get/set image data. You can then draw the buffer Bitmap to the screen to show the rendered image.

Using the Lockbits method to access image data

If you want to render other graphics, you need to use a Graphics object, which will output the result of the drawing operations to the target it was created for. It can be used for a control (Control.CreateGraphics) or a Bitmap (Graphics.FromImage). You would probably want to look into a GDI+ tutorial.

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05-09-2010, 02:24 AM

s33k-n-d3str0y s33k-n-d3str0y is offline

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Join Date: May 2010

Posts: 6

understanding logic

first of all thanks for your relpy..

i have to draw the screen when following opcode appears in ROM

Dxyn - DRW Vx, Vy, nibble
(where x and y are 4 bit constant)
(V(0-F) are 16 register of 8-bit each, VF register is used as flag for some operations)

the Dxyn Instruction opcode is break and read byte by byte as...
opcode1 = D //any thing which is replaced by D goes in opcode1
opcode2 = x //any thing which is replaced by x in opcode goes here
opcode3 = y // any thing which is replaced by y in opcode goes here
opcode4 = n // any thing which is replaced by n in opcode goes here

the instruction say, Display n-byte sprite starting at memory location I at (Vx, Vy), set VF = collision.

The interpreter reads n bytes from memory, starting at the address stored in I. These bytes are then displayed as sprites on screen at coordinates (Vx, Vy). Sprites are XORed onto the existing screen. If this causes any pixels to be erased, VF is set to 1, otherwise it is set to 0. If the sprite is positioned so part of it is outside the coordinates of the display, it wraps around to the opposite side of the screen.

the code i have provided the DrawSprite() functions work as..

v(&HF) = 0 //initially VF register flag is set to 0
x = v(opcode2) * 4 //getting x-cordinate from instruction opcode
y = v(opcode3) * 4 //getting y-cordinates from instruction opcode

//now the forloop comes which is runnig 0 to opcode4 -1; where opcode 4 is the address of memory loaction

For j = 0 To opcode4 - 1
datax = ram(Index + j) // let suppose at any moment the value of index is 922
// when the drawSprite() function is called, it say copy
// the data of memory location ram(index+j) to datax
/////////////////////////////////////////////////////////////////////////////////////
now the following code comes which is my problem to understand that why we are comapring datax>=64, datax>=32 so on?????????? and why is 'i' incrementing??? (i is declared as a byte)
/////////////////////////////////////////////////////////////////////////////////////

Code:

 i = 0
            If datax >= 64 Then
                DrawScreen()
                datax = datax - 64
            End If
            i = i + 1
            If datax >= 32 Then
                DrawScreen()
                datax = datax - 32
            End If
            i = i + 1
            If datax >= 16 Then
                DrawScreen()
                datax = datax - 16
            End If
            i = i + 1
            If datax >= 8 Then
                DrawScreen()
                datax = datax - 8
            End If
            i = i + 1
            If datax >= 4 Then
                DrawScreen()
                datax = datax - 4
            End If
            i = i + 1
            If datax >= 2 Then
                DrawScreen()
                datax = datax - 2
            End If
            i = i + 1
            If datax >= 1 Then
                DrawScreen()
                datax = datax - 1
            End If
        Next j

Last edited by s33k-n-d3str0y; 05-09-2010 at 02:25 AM. Reason: some spelling mistakes

05-09-2010, 01:51 PM

snarfblam

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Join Date: Apr 2005

Location: USA

Posts: 871

Just to be clear, I'm not particularly familiar with Chip 8. Anyways, this code:

Code:

            If datax >= 64 Then
                DrawScreen()
                datax = datax - 64
            End If
            i = i + 1
            If datax >= 32 Then
                DrawScreen()
                datax = datax - 32
            End If

' ...

Appears to be checking bits of the byte. The first bit represents a value of 64, the second 32, so on. If you aren't familiar with binary math, you probably aren't prepared to emulate (implement?) Chip 8. If you are, this is the same as

Code:

If datax And 64 = 64 Then ' Is bit set
    DrawScreen()
    DataX = DataX And Not 64 ' Clear bit
End If

I have no idea what DrawScreen() does, and again, I don't know any of the details of Chip 8, so that's about all I can tell you. I can take a guess that i is meant to represent the index of the bit being checked.

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