Help on Bresenham Line Algo

[ASMCoderD]

Hello everyone.

I am having trouble implementing a bresenham line algorithm. I have tried for a few days without success. This is for an external .DLL
Note that I do know how to plot a pixel to the screen. Could anyone give me an example.

Thanks in advance.

[raymond]

The easiest way to draw a strait line is to use Windows "LineTo" function (unless you are trying to do that under 16-bit DOS as homework :().

[dedndave]

i played with Bresenham line and circle routines - about 10 years ago - got them working ok - don't remember the code   :bg
post the code you have in a zip   :U
but, google is your friend - lol - there are a lot of examples online

[Farabi]

I dont know about bresenham algo, but if you are going to make a line function this would help.

1. Get the Hypotenusa (This is my term for the distance between 2 point)

Code Select Expand


dx=x2-x1
dy=y2-y1

dx=dx*dx
dy=dy*dy

hyp=sqrt(dx+dy)



Then make a loop for hyp times.

Code Select Expand


loop_start:
pos_x= loop_cnt/hyp *hyp
pos_y=loop_cnt/hyp*hyp
jmp loop_start


I dont remember it well since I created it 3 years ago.
But you can always check Donkey Graphics lib for this algo.

[ASMCoderD]

Hello Everone:

Actually, I got the Bresenham algorithm working but I ran into secondary problems. The algorithm works but I don't have enough variables (32 bit: DWORD) left. There's EBP and ESP but those don't work with the C or STDCALL conventions (There're reserved). I tried the BASIC Convention but my .def file gives errors. Could anyone tell me how to setup the BASIC calling convention?  I am on windows, so thanks for the LineTo function, still, I need to know how to use the BASIC convention.

Thanks all for the responses!

[dedndave]

i think it is similar to C, except the calling parameters are pushed in reverse order

[ASMCoderD]

I know that but when I make a procedure in my asm file:

ProcName Proc BASIC, Arg1:DWORD, Arg2:DWORD

;code here

endp

and then put in my .def file:

EXPORTS ProcName

I get an error about error an .def file. How do I fix this?

[ASMCoderD]

Sorry to double post here, but if it isn't possible to use the BASIC convention, can I link to another routine to finish without losing my current values in my routine?

[jj2007]

It would be a lot easier to understand your problems if you posted your code, as everybody does.
Normally, you cannot run out of variables - out of registers, yes, but you need registers only for really speed-critical tasks. For all other purposes, local or global variables are just fine...

[ASMCoderD]

Therein could lie my problem. Excuse me for sounding silly here, but what are local and global variables? I am used to only using registers.

Thanks!

[dedndave]

they are essentially memory locations
local variables are more or less temporary with scope inside the procedure
generally speaking, local variables are assigned space on the stack and are accessed by [ebp-4*n]
global variables have scope outside the procedure
generally speaking, global variables are allocated a permanent memory location

I am having trouble implementing a bresenham line algorithm. I have tried for a few days without
success. This is for an external .DLL Note that I do know how to plot a pixel to the screen.

as Jochen has suggested, this doesn't tell us very much   :P
we have no idea what your problem really is
to help you make better posts, pretend you were trying to answer the question(s) you are asking
then ask yourself, "is there enough information there for us to provide help ?"

[jj2007]

what are local and global variables?

Have a look at the snippet posted here. Global variables are defined in .data (initialised with any value you like) or .data? (zero). They are marginally slower than LOCAL variables but have the advantage to be permanent.

Note also that you can use eax, ebx, ecx, edx, esi, edi but are supposed to preserve ebx esi edi by pushing them at the start of a procedure and popping them in reversed order before the ret statement. Sorry if that is too obvious :wink

[dedndave]

Jochen - i thought the fastest addressing mode was immed direct - no ?

        mov     eax,SomeLabel

faster than

        mov     eax,[ebp-4]

am i wrong (again  :P )

[jj2007]

Jochen - i thought the fastest addressing mode was immed direct - no ?

        mov     eax,SomeLabel

faster than

        mov     eax,[ebp-4]

am i wrong (again  :P )

No idea :bg

Code Select Expand

530     cycles for [ebp]
529     cycles for [MyDword]


.nolist
include \masm32\include\masm32rt.inc
.686
include \masm32\macros\timers.asm         ; get them from the Masm32 Laboratory
LOOP_COUNT   = 100000

.data?
MyDword   dd ?

.code
start:
   sub ebp, 4
   counter_begin LOOP_COUNT, HIGH_PRIORITY_CLASS
      REPEAT 100
      mov ecx, [ebp]
      mov eax, [ebp]
      mov [ebp], ecx
      mov [ebp], eax
      ENDM
   counter_end
   add ebp, 4
   print str$(eax), 9, "cycles for [ebp]", 13, 10

   counter_begin LOOP_COUNT, HIGH_PRIORITY_CLASS
      REPEAT 100
      mov ecx, MyDword
      mov eax, MyDword
      mov MyDword, ecx
      mov MyDword, eax
      ENDM
   counter_end
   print str$(eax), 9, "cycles for [MyDword]", 13, 10

   inkey chr$(13, 10, "--- ok ---", 13)
   exit
end start

[ASMCoderD]

Here is my code:

Code Select Expand

MyLine proc C, Layer:DWORD, Xpos:DWORD, Ypos:DWORD, Xpos2:DWORD, Ypos2:DWORD, Col:DWORD
    local ek:DWORD
    local y:DWORD
    local x:DWORD

    mov eax, Xpos
    mov ebx, Xpos2
    .if eax > ebx
        xchg eax, ebx
    .endif

    mov ecx, Ypos
    mov edx, Ypos2
    .if ecx > edx
        xchg ecx, edx
    .endif


    mov edi, ebx
    sub edi, eax ; dx
   
    mov esi, edx
    sub esi, ecx ; dy
   
    mov edx, esi
    shl edx, 1
    sub edx, edi
    mov ek, edx ; ek

    mov esi, ek
    add esi, edi ; dn
   
    mov edx, ek
    sub edx, edi
    mov edi, edx ; dp
   
    mov x, ebx ; x   
   
    draw:
    inc eax

    .if ek < 0
        add ek, esi
    .else
        add ek, edi
        inc ecx
    .endif

    mov edx, ecx
    mov y, edx
    shl y, 6
    shl edx, 8
    add edx, y
    add edx, eax
    add edx, dword ptr [Layer]
    add edx, 4
    mov ebx, dword ptr [Col]
    mov dword ptr [edx], ebx
   
    .if eax <= x
        jmp draw
    .endif

    ret
   
MyLine endp

I figured out very quickly how to use local integers and that solved one problem. However, the new problem seems to be here:

Code Select Expand


    .if ek < 0
        add ek, esi
    .else
        add ek, edi
        inc ecx
    .endif

I am not sure if it exits right. It seems to draw an even diagonal line. It may be a problem with the algo. I'm not sure however, I could be looking at the wrong area.

Thanks for all the help so far, I really appreciate it.