int DrawMyLine(int x0, int y0, // starting position
int x1, int y1, // ending position
UCHAR color, // color index
UCHAR *vb_start, int lpitch) // video buffer and memory pitch
{
//x1>x0
int dx,dy,dx2,dy2,x_inc,y_inc,slope,error;
dx=x1-x0;
dy=y1-y0;
error=2*dy-dx;
slope=dy/dx;
y_inc=lpitch+slope;
x_inc=1;
int e_move=2*dy;
int ne_move=2*(dy-dx);
vb_start=vb_start+x0+y0*lpitch;
for(int x=x0;x<=x1;x++)
{
*vb_start=color;
if(error<=0)
{
vb_start+=x_inc;
error+=e_move;
}
else
{
vb_start+=x_inc;
vb_start+=y_inc;
error+=ne_move;
}
}
return 0;
}
Bresenhams Algorithm
Author
Hey guys , i ve translated the bresenham algorithm which i had read from the following text.
http://gamedev.cs.colorado.edu/tutorials/Bresenham.pdf
now the only slight problem i m facing is , the increment for Y , which the text suggests should be 1 , the algorithm dosen't perform well with it , and ends up drawing a blunder.When i take it up logically , the y co-ordinate must increase by the slope , instead of 1 ,per x co-orinate , there must be something i am missing out. (i guess error handling is only what makes this algo differ from mid-point algorithm - which if i am not wrong is just increasing y per x )Though the program works well with the slope , but it adds a division , ok so i dont want to be Mr.Optimization but is there any other way around this ??
(This small section i ve written which is for the first quadrant only , i guess some small changes and this can be incorporated in the others too :)
basically, y_delta is only 1 if the line changes more in the y direction than in the x direction. Otherwise it is the x_delta that will be 1. (i.e. you always step by 1 in the longest dimension, while the shorter dimension is only incremented sometimes, based on the "(error < 0)" criterion)
here are some other articles here on gamedev:
article 1
article 2
here are some other articles here on gamedev:
article 1
article 2
If I'm reading the code correctly, you have code for the case where the slope is less than or equal to 1.
Here's how I solved it for that case:
for 0 .. dx - 1
draw a pixel at x0, y0
if the error is greater than or equal to 0
then, increment y0 by the y increment and the error becomes error minux 2*dx
increment x0 by the x increment
error becomes error plus 2 * dy
end for
The if statement in the loop check the error. This influences whether the next point should be (xi+1, yi) or (xi+1, yi+1). (note: read the i's as subscripts). This is what lonesock was talking about.
Hope this helps.
[Edited by - arcadion on July 9, 2005 3:39:51 PM]
Here's how I solved it for that case:
for 0 .. dx - 1
draw a pixel at x0, y0
if the error is greater than or equal to 0
then, increment y0 by the y increment and the error becomes error minux 2*dx
increment x0 by the x increment
error becomes error plus 2 * dy
end for
The if statement in the loop check the error. This influences whether the next point should be (xi+1, yi) or (xi+1, yi+1). (note: read the i's as subscripts). This is what lonesock was talking about.
Hope this helps.
[Edited by - arcadion on July 9, 2005 3:39:51 PM]
Author
thanks for the reply's , sorry i forgot to mention , as i was just starting out i constrained my self from passing values which would mess it up.[ie dx << dy ] , i 'll check those articles :)
Author
Man , this is really getting to me :'(
This is what the second articel suggests for drawing lines with a bresenham algorithm.
which is pretty much what i am doing , i guess there is some fault in this line
y_inc=lpitch+1;
right now i am only passing co-ordinates which the program can handle , eg 0,0,320,240.
now when i pass the above set of co-ordinates , i get the perfect result , provided my y_increment is
y_inc=lpitch+slope;
but , if i change the y_inc according to the algorithm , ie
y_inc=lpitch+1;
the line being drawn is not proper.
arcadion , could you please elaborate on the error handling part , as i am completely aware why we are adding 2*dx and 2*(dy-dx) in this case , but i am unable to reach a conclusion why what you suggest is done.I do have a book which suggests exactly what you say but , it dosent carry any information on the subject.
Here's the entire code , those who are too lazy to type :P
This is what the second articel suggests for drawing lines with a bresenham algorithm.
PutPixel(x, y); { Draw a pixel at the current point }if d < 0 then d := d + (2 * deltay)else begin d := d + 2 * (deltay - deltax); y := y + 1; end;x := x + 1;which is pretty much what i am doing , i guess there is some fault in this line
y_inc=lpitch+1;
right now i am only passing co-ordinates which the program can handle , eg 0,0,320,240.
now when i pass the above set of co-ordinates , i get the perfect result , provided my y_increment is
y_inc=lpitch+slope;
but , if i change the y_inc according to the algorithm , ie
y_inc=lpitch+1;
the line being drawn is not proper.
arcadion , could you please elaborate on the error handling part , as i am completely aware why we are adding 2*dx and 2*(dy-dx) in this case , but i am unable to reach a conclusion why what you suggest is done.I do have a book which suggests exactly what you say but , it dosent carry any information on the subject.
Here's the entire code , those who are too lazy to type :P
#define WIN32_LEAN_AND_MEAN #define INITGUID#include <windows.h> #include <windowsx.h> #include <mmsystem.h>#include <iostream.h> #include <conio.h>#include <stdlib.h>#include <malloc.h>#include <memory.h>#include <string.h>#include <stdarg.h>#include <stdio.h> #include <math.h>#include <io.h>#include <fcntl.h>#include <ddraw.h> // include directdraw// DEFINES ////////////////////////////////////////////////// defines for windows #define WINDOW_CLASS_NAME "WINCLASS1"// default screen size#define SCREEN_WIDTH 640 // size of screen#define SCREEN_HEIGHT 480#define SCREEN_BPP 8 // bits per pixel#define BITMAP_ID 0x4D42 // universal id for a bitmap#define MAX_COLORS_PALETTE 256// TYPES //////////////////////////////////////////////////////// basic unsigned typestypedef unsigned short USHORT;typedef unsigned short WORD;typedef unsigned char UCHAR;typedef unsigned char BYTE;// PROTOTYPES //////////////////////////////////////////////int DDraw_Fill_Surface(LPDIRECTDRAWSURFACE7 lpdds,int color);int Draw_Line(int x0, int y0, int x1, int y1, UCHAR color, UCHAR *vb_start, int lpitch);// MACROS /////////////////////////////////////////////////// tests if a key is up or down#define KEYDOWN(vk_code) ((GetAsyncKeyState(vk_code) & 0x8000) ? 1 : 0)#define KEYUP(vk_code) ((GetAsyncKeyState(vk_code) & 0x8000) ? 0 : 1)// initializes a direct draw struct#define DDRAW_INIT_STRUCT(ddstruct) { memset(&ddstruct,0,sizeof(ddstruct)); ddstruct.dwSize=sizeof(ddstruct); }// GLOBALS ////////////////////////////////////////////////HWND main_window_handle = NULL; // globally track main windowint window_closed = 0; // tracks if window is closedHINSTANCE hinstance_app = NULL; // globally track hinstance// directdraw stuffLPDIRECTDRAW7 lpdd = NULL; // dd objectLPDIRECTDRAWSURFACE7 lpddsprimary = NULL; // dd primary surfaceLPDIRECTDRAWSURFACE7 lpddsback = NULL; // dd back surfaceLPDIRECTDRAWPALETTE lpddpal = NULL; // a pointer to the created dd paletteLPDIRECTDRAWCLIPPER lpddclipper = NULL; // dd clipperPALETTEENTRY palette[256]; // color palettePALETTEENTRY save_palette[256]; // used to save palettesDDSURFACEDESC2 ddsd; // a direct draw surface description structDDBLTFX ddbltfx; // used to fillDDSCAPS2 ddscaps; // a direct draw surface capabilities structHRESULT ddrval; // result back from dd callsDWORD start_clock_count = 0; // used for timingchar buffer[80]; // general printing buffer// FUNCTIONS ////////////////////////////////////////////////inline int Draw_Pixel(int x, int y,int color, UCHAR *video_buffer, int lpitch){// this function plots a single pixel at x,y with colorvideo_buffer[x + y*lpitch] = color;// return successreturn(1);} // end Draw_Pixel/////////////////////////////////////////////////////////////int DDraw_Fill_Surface(LPDIRECTDRAWSURFACE7 lpdds,int color){DDBLTFX ddbltfx; // this contains the DDBLTFX structure// clear out the structure and set the size field DDRAW_INIT_STRUCT(ddbltfx);// set the dwfillcolor field to the desired colorddbltfx.dwFillColor = color; // ready to blt to surfacelpdds->Blt(NULL, // ptr to dest rectangle NULL, // ptr to source surface, NA NULL, // ptr to source rectangle, NA DDBLT_COLORFILL | DDBLT_WAIT, // fill and wait &ddbltfx); // ptr to DDBLTFX structure// return successreturn(1);} // end DDraw_Fill_Surface///////////////////////////////////////////////////////////////int Draw_Line(int x0, int y0, // starting position int x1, int y1, // ending position UCHAR color, // color index UCHAR *vb_start, int lpitch) // video buffer and memory pitch{// this function draws a line from xo,yo to x1,y1 using differential error// terms (based on Bresenahams work)int dx, // difference in x's dy, // difference in y's dx2, // dx,dy * 2 dy2, x_inc, // amount in pixel space to move during drawing y_inc, // amount in pixel space to move during drawing error, // the discriminant i.e. error i.e. decision variable index; // used for looping// pre-compute first pixel address in video buffervb_start = vb_start + x0 + y0*lpitch;// compute horizontal and vertical deltasdx = x1-x0;dy = y1-y0;// test which direction the line is going in i.e. slope angleif (dx>=0) { x_inc = 1; } // end if line is moving rightelse { x_inc = -1; dx = -dx; // need absolute value } // end else moving left// test y component of slopeif (dy>=0) { y_inc = lpitch; } // end if line is moving downelse { y_inc = -lpitch; dy = -dy; // need absolute value } // end else moving up// compute (dx,dy) * 2dx2 = dx << 1;dy2 = dy << 1;// now based on which delta is greater we can draw the lineif (dx > dy) { // initialize error term error = dy2 - dx; // draw the line for (index=0; index <= dx; index++) { // set the pixel *vb_start = color; // test if error has overflowed if (error >= 0) { error-=dx2; // move to next line vb_start+=y_inc; } // end if error overflowed // adjust the error term error+=dy2; // move to the next pixel vb_start+=x_inc; } // end for } // end if |slope| <= 1else { // initialize error term error = dx2 - dy; // draw the line for (index=0; index <= dy; index++) { // set the pixel *vb_start = color; // test if error overflowed if (error >= 0) { error-=dy2; // move to next line vb_start+=x_inc; } // end if error overflowed // adjust the error term error+=dx2; // move to the next pixel vb_start+=y_inc; } // end for } // end else |slope| > 1// return successreturn(1);} // end Draw_Line///////////////////////////////////////////////////////////////int Draw_Text_GDI(char *text, int x,int y, COLORREF color, LPDIRECTDRAWSURFACE7 lpdds){// this function draws the sent text on the sent surface // using color index as the color in the paletteHDC xdc; // the working dc// get the dc from surfaceif (FAILED(lpdds->GetDC(&xdc))) return(0);// set the colors for the text upSetTextColor(xdc,color);// set background mode to transparent so black isn't copiedSetBkMode(xdc, TRANSPARENT);// draw the text aTextOut(xdc,x,y,text,strlen(text));// release the dclpdds->ReleaseDC(xdc);// return successreturn(1);} // end Draw_Text_GDIint DrawMyLine(int x0, int y0, // starting position int x1, int y1, // ending position UCHAR color, // color index UCHAR *vb_start, int lpitch) // video buffer and memory pitch{//x1>x0int dx,dy,dx2,dy2,x_inc,y_inc,slope,error;dx=x1-x0;dy=y1-y0;error=2*dy-dx;slope=dy/dx;y_inc=lpitch+1;x_inc=1;int e_move=2*dy;int ne_move=2*dy-2*dx;vb_start=vb_start+x0+y0*lpitch;int y=0;for(int x=x0;x<=x1-1;x++){ *vb_start=color; vb_start+=x_inc; if(error<0) { error+=e_move; } else { vb_start+=y_inc; error+=ne_move; y+=1; }}sprintf(buffer,"Value of x = %d y=%d",x,y);Draw_Text_GDI(buffer,0,0,255,lpddsprimary);return 0;}LRESULT CALLBACK WindowProc(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam){// this is the main message handler of the systemPAINTSTRUCT ps; // used in WM_PAINTHDC hdc; // handle to a device contextchar buffer[80]; // used to print strings// what is the message switch(msg) { case WM_CREATE: { // do initialization stuff here // return success return(0); } break; case WM_PAINT: { // simply validate the window hdc = BeginPaint(hwnd,&ps); // end painting EndPaint(hwnd,&ps); // return success return(0); } break; case WM_DESTROY: { // kill the application, this sends a WM_QUIT message PostQuitMessage(0); // return success return(0); } break; default:break; } // end switch// process any messages that we didn't take care of return (DefWindowProc(hwnd, msg, wparam, lparam));} // end WinProc///////////////////////////////////////////////////////////int Game_Main(void *parms = NULL, int num_parms = 0){// this is the main loop of the game, do all your processing// here// make sure this isn't executed againif (window_closed) return(0);// for now test if user is hitting ESC and send WM_CLOSEif (KEYDOWN(VK_ESCAPE)) { PostMessage(main_window_handle,WM_CLOSE,0,0); window_closed = 1; } // end if// lock primary bufferDDRAW_INIT_STRUCT(ddsd);if (FAILED(lpddsprimary->Lock(NULL,&ddsd, DDLOCK_WAIT | DDLOCK_SURFACEMEMORYPTR, NULL)))return(0);/*// draw 1000 random linesfor (int index=0; index < 1000; index++) { Draw_Line(rand()%SCREEN_WIDTH, rand()%SCREEN_HEIGHT, rand()%SCREEN_WIDTH, rand()%SCREEN_HEIGHT, rand()%256, (UCHAR *)ddsd.lpSurface, ddsd.lPitch); } // end for index*/DrawMyLine(0,0,320,240,255,(UCHAR*)ddsd.lpSurface,ddsd.lPitch);//DrawMyLine(0,0,320,240,255,(UCHAR*)ddsd.lpSurface,ddsd.lPitch);// unlock primary bufferif (FAILED(lpddsprimary->Unlock(NULL))) return(0);// wait a secSleep(33);// return success or failure or your own return code herereturn(1);} // end Game_Main////////////////////////////////////////////////////////////int Game_Init(void *parms = NULL, int num_parms = 0){// this is called once after the initial window is created and// before the main event loop is entered, do all your initialization// here// create IDirectDraw interface 7.0 object and test for errorif (FAILED(DirectDrawCreateEx(NULL, (void **)&lpdd, IID_IDirectDraw7, NULL))) return(0);// set cooperation to full screenif (FAILED(lpdd->SetCooperativeLevel(main_window_handle, DDSCL_FULLSCREEN | DDSCL_ALLOWMODEX | DDSCL_EXCLUSIVE | DDSCL_ALLOWREBOOT))) return(0);// set display mode to 640x480x8if (FAILED(lpdd->SetDisplayMode(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP,0,0))) return(0);// clear ddsd and set sizeDDRAW_INIT_STRUCT(ddsd); // enable valid fieldsddsd.dwFlags = DDSD_CAPS;// request primary surfaceddsd.ddsCaps.dwCaps = DDSCAPS_PRIMARYSURFACE;// create the primary surfaceif (FAILED(lpdd->CreateSurface(&ddsd, &lpddsprimary, NULL))) return(0);// build up the palette data arrayfor (int color=1; color < 255; color++) { // fill with random RGB values palette.peRed = rand()%<span class="cpp-number">256</span>;<br> palette.peGreen = rand()%<span class="cpp-number">256</span>;<br> palette.peBlue = rand()%<span class="cpp-number">256</span>;<br><br> <span class="cpp-comment">// set flags field to PC_NOCOLLAPSE</span><br> palette.peFlags = PC_NOCOLLAPSE;<br> } <span class="cpp-comment">// end for color</span><br><br><span class="cpp-comment">// now fill in entry 0 and 255 with black and white</span><br>palette[<span class="cpp-number">0</span>].peRed = <span class="cpp-number">0</span>;<br>palette[<span class="cpp-number">0</span>].peGreen = <span class="cpp-number">0</span>;<br>palette[<span class="cpp-number">0</span>].peBlue = <span class="cpp-number">0</span>;<br>palette[<span class="cpp-number">0</span>].peFlags = PC_NOCOLLAPSE;<br><br>palette[<span class="cpp-number">255</span>].peRed = <span class="cpp-number">255</span>;<br>palette[<span class="cpp-number">255</span>].peGreen = <span class="cpp-number">255</span>;<br>palette[<span class="cpp-number">255</span>].peBlue = <span class="cpp-number">255</span>;<br>palette[<span class="cpp-number">255</span>].peFlags = PC_NOCOLLAPSE;<br><br><span class="cpp-comment">// create the palette object</span><br><span class="cpp-keyword">if</span> (FAILED(lpdd->CreatePalette(DDPCAPS_8BIT | DDPCAPS_ALLOW256 | <br> DDPCAPS_INITIALIZE, <br> palette,&lpddpal, NULL)))<br><span class="cpp-keyword">return</span>(<span class="cpp-number">0</span>);<br><br><span class="cpp-comment">// finally attach the palette to the primary surface</span><br><span class="cpp-keyword">if</span> (FAILED(lpddsprimary->SetPalette(lpddpal)))<br> <span class="cpp-keyword">return</span>(<span class="cpp-number">0</span>);<br><br><span class="cpp-comment">// clear the primary surface off</span><br>DDraw_Fill_Surface(lpddsprimary, <span class="cpp-number">0</span> );<br><br><br><span class="cpp-comment">// return success or failure or your own return code here</span><br><span class="cpp-keyword">return</span>(<span class="cpp-number">1</span>);<br><br>} <span class="cpp-comment">// end Game_Init</span><br><br><span class="cpp-comment">/////////////////////////////////////////////////////////////</span><br><br><span class="cpp-keyword">int</span> Game_Shutdown(<span class="cpp-keyword">void</span> *parms = NULL, <span class="cpp-keyword">int</span> num_parms = <span class="cpp-number">0</span>)<br>{<br><span class="cpp-comment">// this is called after the game is exited and the main event</span><br><span class="cpp-comment">// loop while is exited, do all you cleanup and shutdown here</span><br><br><br><span class="cpp-comment">// first the palette</span><br><span class="cpp-keyword">if</span> (lpddpal)<br> {<br> lpddpal->Release();<br> lpddpal = NULL;<br> } <span class="cpp-comment">// end if</span><br><br><span class="cpp-comment">// now the primary surface</span><br><span class="cpp-keyword">if</span> (lpddsprimary)<br> {<br> lpddsprimary->Release();<br> lpddsprimary = NULL;<br> } <span class="cpp-comment">// end if</span><br><br><span class="cpp-comment">// now blow away the IDirectDraw4 interface</span><br><span class="cpp-keyword">if</span> (lpdd)<br> {<br> lpdd->Release();<br> lpdd = NULL;<br> } <span class="cpp-comment">// end if</span><br><br><span class="cpp-comment">// return success or failure or your own return code here</span><br><span class="cpp-keyword">return</span>(<span class="cpp-number">1</span>);<br><br>} <span class="cpp-comment">// end Game_Shutdown</span><br><br><span class="cpp-comment">// WINMAIN ////////////////////////////////////////////////</span><br><br><span class="cpp-keyword">int</span> WINAPI WinMain( HINSTANCE hinstance,<br> HINSTANCE hprevinstance,<br> LPSTR lpcmdline,<br> <span class="cpp-keyword">int</span> ncmdshow)<br>{<br><br>WNDCLASSEX winclass; <span class="cpp-comment">// this will hold the class we create</span><br>HWND hwnd; <span class="cpp-comment">// generic window handle</span><br>MSG msg; <span class="cpp-comment">// generic message</span><br>HDC hdc; <span class="cpp-comment">// graphics device context</span><br><br><span class="cpp-comment">// first fill in the window class stucture</span><br>winclass.cbSize = <span class="cpp-keyword">sizeof</span>(WNDCLASSEX);<br>winclass.style = CS_DBLCLKS | CS_OWNDC | <br> CS_HREDRAW | CS_VREDRAW;<br>winclass.lpfnWndProc = WindowProc;<br>winclass.cbClsExtra = <span class="cpp-number">0</span>;<br>winclass.cbWndExtra = <span class="cpp-number">0</span>;<br>winclass.hInstance = hinstance;<br>winclass.hIcon = LoadIcon(NULL, IDI_APPLICATION);<br>winclass.hCursor = LoadCursor(NULL, IDC_ARROW); <br>winclass.hbrBackground = (HBRUSH)GetStockObject(BLACK_BRUSH);<br>winclass.lpszMenuName = NULL;<br>winclass.lpszClassName = WINDOW_CLASS_NAME;<br>winclass.hIconSm = LoadIcon(NULL, IDI_APPLICATION);<br><br><span class="cpp-comment">// save hinstance in global</span><br>hinstance_app = hinstance;<br><br><span class="cpp-comment">// register the window class</span><br><span class="cpp-keyword">if</span> (!RegisterClassEx(&winclass))<br> <span class="cpp-keyword">return</span>(<span class="cpp-number">0</span>);<br><br><span class="cpp-comment">// create the window</span><br><span class="cpp-keyword">if</span> (!(hwnd = CreateWindowEx(NULL, <span class="cpp-comment">// extended style</span><br> WINDOW_CLASS_NAME, <span class="cpp-comment">// class</span><br> <span class="cpp-literal">"DirectDraw 8-Bit Line Drawing Demo"</span>, <span class="cpp-comment">// title</span><br> WS_POPUP | WS_VISIBLE,<br> <span class="cpp-number">0</span>,<span class="cpp-number">0</span>, <span class="cpp-comment">// initial x,y</span><br> SCREEN_WIDTH,SCREEN_HEIGHT, <span class="cpp-comment">// initial width, height</span><br> NULL, <span class="cpp-comment">// handle to parent </span><br> NULL, <span class="cpp-comment">// handle to menu</span><br> hinstance,<span class="cpp-comment">// instance of this application</span><br> NULL))) <span class="cpp-comment">// extra creation parms</span><br><span class="cpp-keyword">return</span>(<span class="cpp-number">0</span>);<br><br><span class="cpp-comment">// save main window handle</span><br>main_window_handle = hwnd;<br><br><span class="cpp-comment">// initialize game here</span><br>Game_Init();<br><br><span class="cpp-comment">// enter main event loop</span><br><span class="cpp-keyword">while</span>(<span class="cpp-keyword">TRUE</span>)<br> {<br> <span class="cpp-comment">// test if there is a message in queue, if so get it</span><br> <span class="cpp-keyword">if</span> (PeekMessage(&msg,NULL,<span class="cpp-number">0</span>,<span class="cpp-number">0</span>,PM_REMOVE))<br> { <br> <span class="cpp-comment">// test if this is a quit</span><br> <span class="cpp-keyword">if</span> (msg.message == WM_QUIT)<br> <span class="cpp-keyword">break</span>;<br> <br> <span class="cpp-comment">// translate any accelerator keys</span><br> TranslateMessage(&msg);<br><br> <span class="cpp-comment">// send the message to the window proc</span><br> DispatchMessage(&msg);<br> } <span class="cpp-comment">// end if</span><br> <br> <span class="cpp-comment">// main game processing goes here</span><br> Game_Main();<br> <br> } <span class="cpp-comment">// end while</span><br><br><span class="cpp-comment">// closedown game here</span><br>Game_Shutdown();<br><br><span class="cpp-comment">// return to Windows like this</span><br><span class="cpp-keyword">return</span>(msg.wParam);<br><br>} <span class="cpp-comment">// end WinMain</span><br><br><span class="cpp-comment">///////////////////////////////////////////////////////////</span><br><br><br><br><br></pre></div><!–ENDSCRIPT–><br><br><br><br>I am really getting pathetic at this , its been around 2 days since i am trying to figure this out ……HELLLPP!!!
Author
I hate to make this a blog kind of thing , but since there were over 100 views & no solution , i finally figured out what was wrong, so here it goes :)
in the line y_inc=lpitch+1 , i was stepping in the y direction by 1 more , as x was being incremented at every iteration , thus i needed to plot the pixel at (x+1,y) or (x+1,y+1) , what y_inc=lpitch+1 did was plot the pixel at (x+1,y+2) as a result a whole mess :D
but heck it was 4 am when i was trying to debug it :\
in the line y_inc=lpitch+1 , i was stepping in the y direction by 1 more , as x was being incremented at every iteration , thus i needed to plot the pixel at (x+1,y) or (x+1,y+1) , what y_inc=lpitch+1 did was plot the pixel at (x+1,y+2) as a result a whole mess :D
but heck it was 4 am when i was trying to debug it :\
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