Drawing lines and ellipses with DirectDraw

Hey everyone, this is my problem: I want to draw a line and an ellipse, but DirectDraw has no built-in features to do so, except for in VB. Searching through my book and my brain, I came up with only two solutions: manually calculate the position of each pixel, then lock the surface and plot them; or make a call to GetDC, and use GDI to draw the line. The latter is from my unreliable book, and uses the reputedly slow GDI. However, I have no idea if the manual calculate/plot approach would be any faster. Which method should I try?

Using GDI can be slow, true. However, locking the surfaces is pretty slow also and SetPixel is RIDICULOUSLY slow. So, unless you want to write your own SetPixel ( SetPixelV slightly faster.. ) I suggest just using GDI. If you're curious though you can write your own line drawing algorithm. Look up Bresenham on google and you can use his algorithm. There are similar algorithms for elipses, circles, triangles, polygons etc. Many use DDA style algorithms. If this is not you cup of tea ;) then you can use GDI.

Alternatively, you may use a bitmap as the elipse depending on what you are doing and manipulate it accordingly. Just a thought.

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However, locking the surfaces is pretty slow also and SetPixel is RIDICULOUSLY slow.

I'm assuming you mean the GDI SetPixel, since I can't seem to find one in the DX docs... But if that's the case, wouldn't that defeat the purpose of avoiding GDI? :confused:

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So, unless you want to write your own SetPixel

I was sort of thinking of that, actually, by locking the surface and setting the pixels directly. But then, locking the surface is "pretty slow"... Would it still be faster though?

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If you're curious though you can write your own line drawing algorithm.

That could be interesting; I could even try adding special effects I guess, like gradient lines :p

In conclusion: For the moment, I guess I'll use GDI to draw my lines, although if it's worthwhile I'll probably look into making my own line/ellipse things later. Thanks MrWizard! :)

**EDIT**
About using a bitmap for an ellipse, I thought about that... but then wouldn't it take a lot of memory and take even longer to make the blit? (i.e. has to set a lot more pixels)

I would say just use GDI and unless you REALLY see a performance hit don't worry about it. You should be ok just using that. One of the times I lock surfaces is to check collisions. I can't think of too many others where you need to lock the surfaces. I'd say just use GDI you should be fine.

Ok, thanks alot!

Hey, guys (or maybe just MrWizard :D), new question! I trying to make a SetPixel or my own - this is my idea so far:

PHP Code:

//the surface is already locked //pixels contains the data, and is an unsigned char* //ddsd is my DDSURFACEDESC2 filled in with the data bool setPixel(DWORD x, DWORD y, DWORD colour) { if((x * y) > numPixels) return false; unsigned char* ptr = pixels; int bytes_per_pixel = ddsd.ddpfPixelFormat.dwRGBBitCount >> 3; ptr += ((x + (y * ddsd.lPitch >> bytes_per_pixel)) * bytes_per_pixel); if(ddsd.ddpfPixelFormat.dwRGBBitCount == 8) *ptr = (unsigned char)colour; else if(ddsd.ddpfPixelFormat.dwRGBBitCount == 16) *(unsigned short*)ptr = (unsigned short)colour; else if(ddsd.ddpfPixelFormat.dwRGBBitCount == 32) *(DWORD*)ptr = (DWORD)colour; return true; }

Would this code work? Or if it would, would it be too slow or unreliable or something? (I heard that multiplication is a really bad thing to have in graphics code)

**EDIT**
Another idea I had, was instead of the ifs, using a typedef when I lock the surface (i.e. do the if's then instead of now, then "typedef the_type (unsigned char)" or "typedef the_type (unsigned short)"). Would it work if I tried re-typedefing a type?

**EDIT2**
sorry, with all my editing the code, it's getting really jumbled right now...

Tell ya what. I'm leaving to go back to Seattle early Sunday. When I get home I'll post my code for setting and getting pixels. I think its pretty similar but may have slight differences. Talk to you more about it later.

EDIT:

Check your PM's Hunter2, :D

My linedraw

It's for DirectX8 and it only works for 32bit color.
But maybe you can use it. But you have to remove or replace some of the variables with your own (such as m_iScreenWidth and my specific buffer names).

Oh yeah and it uses goto...HAHA..

PHP Code:

void LineDraw(int x1, int y1, int x2, int y2, int r, int g, int b) { LPDIRECT3DSURFACE8 pBackBuffer; D3DLOCKED_RECT D3DLockedRect; HRESULT hr; int *pSurfaceData; int *p; int Color32 = 0x0000000; //ARGB if (m_iBitsPerPixel == 32) { Color32 |= b; Color32 |= (g <<8); Color32 |= (r <<16); } else return; int x, y; int dx, dy; int incx, incy; int balance; if ( (x1<0) || (x1<=m_iScreenWidth) || (y1<0) || (y1>=m_iScreenHeight) || (x2 >= m_iScreenWidth) || (x2 < 0) || (y2<0) || (y2 >= m_iScreenHeight) ) goto LINEDRAWWITHCHECK; //lock backbuffer m_pd3dDevice->GetBackBuffer(0, D3DBACKBUFFER_TYPE_MONO, &pBackBuffer); hr = pBackBuffer->LockRect(&D3DLockedRect, NULL, D3DLOCK_NO_DIRTY_UPDATE); if (hr != D3D_OK) { pLog->Log("Gfx::LineDraw - unable to lock backbuffer"); return; } pSurfaceData = (int*)D3DLockedRect.pBits; if (x2 >= x1) { dx = x2 - x1; incx = 1; } else { dx = x1 - x2; incx = -1; } if (y2 >= y1) { dy = y2 - y1; incy = 1; } else { dy = y1 - y2; incy = -1; } x = x1; y = y1; if (dx >= dy) { dy <<= 1; balance = dy - dx; dx <<= 1; while (x != x2) { //plotpixel p = pSurfaceData; p += (y * (D3DLockedRect.Pitch/4)) + x; *p = Color32; if (balance >= 0) { y += incy; balance -= dx; } balance += dy; x += incx; } //plotpixel p = pSurfaceData; p += (y * (D3DLockedRect.Pitch/4)) + x; *p = Color32; } else { dx <<= 1; balance = dx - dy; dy <<= 1; while (y != y2) { //plotpixel p = pSurfaceData; p += (y * (D3DLockedRect.Pitch/4)) + x; *p = Color32; if (balance >= 0) { x += incx; balance -= dy; } balance += dx; y += incy; } //plotpixel p = pSurfaceData; p += (y * (D3DLockedRect.Pitch/4)) + x; *p = Color32; } //unlock backbuffer hr = pBackBuffer->UnlockRect(); if (hr != D3D_OK) { pLog->Log("Gfx::Unable to unlock backbuffer. "); } return; LINEDRAWWITHCHECK: //lock backbuffer m_pd3dDevice->GetBackBuffer(0, D3DBACKBUFFER_TYPE_MONO, &pBackBuffer); hr = pBackBuffer->LockRect(&D3DLockedRect, NULL, D3DLOCK_NO_DIRTY_UPDATE); if (hr != D3D_OK) return; pSurfaceData = (int*)D3DLockedRect.pBits; if (x2 >= x1) { dx = x2 - x1; incx = 1; } else { dx = x1 - x2; incx = -1; } if (y2 >= y1) { dy = y2 - y1; incy = 1; } else { dy = y1 - y2; incy = -1; } x = x1; y = y1; if (dx >= dy) { dy <<= 1; balance = dy - dx; dx <<= 1; while (x != x2) { //plotpixel if ( (x >=0) && (x <m_iScreenWidth) && (y >=0) && (y < m_iScreenHeight) ) { p = pSurfaceData; p += (y * (D3DLockedRect.Pitch/4)) + x; *p = Color32; } if (balance >= 0) { y += incy; balance -= dx; } balance += dy; x += incx; } //plotpixel if ( (x >=0) && (x <m_iScreenWidth) && (y >=0) && (y < m_iScreenHeight) ) { p = pSurfaceData; p += (y * (D3DLockedRect.Pitch/4)) + x; *p = Color32; } } else { dx <<= 1; balance = dx - dy; dy <<= 1; while (y != y2) { //plotpixel if ( (x >=0) && (x <m_iScreenWidth) && (y >=0) && (y < m_iScreenHeight) ) { p = pSurfaceData; p += (y * (D3DLockedRect.Pitch/4)) + x; *p = Color32; } if (balance >= 0) { x += incx; balance -= dy; } balance += dx; y += incy; } //plotpixel if ( (x >=0) && (x <m_iScreenWidth) && (y >=0) && (y < m_iScreenHeight) ) { p = pSurfaceData; p += (y * (D3DLockedRect.Pitch/4)) + x; *p = Color32; } } //unlock backbuffer hr = pBackBuffer->UnlockRect(); if (hr != D3D_OK) pLog->Log("Gfx::LineDraw() - Unable to unlock backbuffer."); }

Unless you're making a REALLY graphics-intensive game, the GDI is fine.
It's actually not that slow.

Ok, thanks everyone.

P.S.
I really needed the SetPixel(), since that's doing all the background-drawing (i.e. drawing stars), and in the GDI version the star-drawing took something like the 4th longest time to do.