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# Drawing Lines in DirectDraw

## 6 posts in this topic

DirectDraw doesn't support line drawing... Check CGPP or preferably Abrash' black book of graphics programming for a really fast line drawing algorithm (it also has a fast one for antialiased lines)...

/Niels

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You can draw your own lines by plotting pixels on a surface. I can dig up some functions if you need them, but at least 3 books I've seen on DirectX go into this.
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Well. You want to draw lines.

Use DrawPrimitive with the LINE function.

If you dont have the D3DIM ( which you should have, its very simple to do lines with it ) , you either lock the surface
down and pixel it. Or you use the the GDI.

Locking the surface down and using a line
drawing routine would be the best if you
dont use D3DIM.

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Well, I hope this helps some. It just draws a straight vertical line. Pretty uselesse, but its just a few lines of code away from what you want

//--------------------------------------------------------------------------------------------
// Draw_VLine()
//--------------------------------------------------------------------------------------------
BOOL Draw_VLine( LPDIRECTDRAWSURFACE4 lpDDSTemp, int x, int y, int y2, WORD rgbColor )
{
int index;
WORD *wPixels;
DDSURFACEDESC2 ddsd;

ZeroMemory( &ddsd, sizeof( ddsd ) );
ddsd.dwSize = sizeof( ddsd );

if ( FAILED (lpDDSTemp->Lock( NULL, &ddsd, DDLOCK_WAIT | DDLOCK_WRITEONLY, NULL ) ) )
return Error( "> Error: Couldn't lock the Temp surface.\n> Function: Draw_Pixel().\n", DEBUG );

wPixels = ( WORD * )ddsd.lpSurface;

for ( index = 0; index <= ( y2 - y ); index++ )
wPixels[( y + index ) * ( ddsd.lPitch >> 1 ) + x] = rgbColor;

if ( FAILED (lpDDSTemp->Unlock( NULL ) ) )
return Error( "> Error: Couldn't unlock the Temp surface.\n> Function: Draw_Pixel().\n", DEBUG );

return TRUE;
}

------------------
- mallen22@concentric.net
- http://members.tripod.com/mxf_entertainment/

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Here's some more! line drawing routines. Even though these are not written in
assembly, they might actually be faster than ones written in assembly if
you have VC++6.0 and optimizations turned on.

Don't ask me why this is faster, I guess MSVC++ can write better
assembly than me.

The locking/unlocking of the surface is done outside the function, so
you can use them several times if you need to draw more than one line, like
a rectangle. surface_buffer is your pointer to the DD surface. Oh yeah,
these were written for 16-bit color.

But, if you want to speed it up even more, just move everything
into one function.

code:
//// Draw a horizontal line (dy=0) from left to right. //void  Draw_Primitive_HLine_No_Clip(INT width, WORD color, WORD *surface_buffer) {  while(width--) {    // set the color and advance one pixel    *surface_buffer++ = color; }  }

code:
//// Draw a vertical line (dx=0) from top to bottom.//voidDraw_Primitive_VLine_No_Clip(INT height, WORD color, WORD *surface_buffer, DWORD pitch) {  while(height--) {    // set the pixel    *surface_buffer = color;    // move to the next scanline pixel    surface_buffer += pitch; }  }

Reaver

[This message has been edited by Reaver (edited November 05, 1999).]

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Personally, I wouldn't trust the VC optimizer, I got a double up in speed by handcoding a few inner loops (compared to optimized C++), and I'm NOT a Ix86 ASM wizard.

And I still recommend reading Abrash' black book - He starts out with plain Bresenhams line drawing, covers "run-length slice drawing", and ends up antialiasing it... Check it out - that book can not be recommended enough !

/Niels

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Hello everybody. I have a teensy little
question.

In DirectDraw I am writing a dodgy asteroids
clone. Now what I need is the ability to
draw straight lines, even quickly if possible.

Does Direct-X supply primitives?
How else could I do it? GDI?

I have little windows programming experience,
but if it's there's no quick way availble I
can always do a port of my DOS code.

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