GDI+ 3D Demo using C#

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Introduction

This small program was developed as part of my learning of C# with GDI+ features. It also uses code I have authored on a previous platform (Amiga) with C language. Being a newbie to C# and GDI+, I would very much appreciate helpful feedback, along with any demo animation suggestions.

Using the code

Build and run the example as a Windows Form with your C# compiler. I used Visual Studio, and for rapid coding, I have found the free Snippet Compiler by Jeff Key at www.sliver.com is excellent. When the program is run, you should see a spiraled sphere shape in gradient colors and initially you are looking toward a sphere pole.

I'll go over some points in the program code and the procedures used.

First, a Bitmap object, bmap, is created, which is not really needed if you use the System.Drawing functions, but I used it to start exploring double buffering. Also, a bitmap object is necessary in order to use the Bitmap.SetPixel method. The other Bitmap object, bm, is not used for drawing. Its function is to clear the Form bitmap so that a new rotated view of the sphere will not blit from the hidden bitmap, bmap, onto the Windows Form and leave artifacts from previous views. GDI has blitter functions available specifically for this operation but GDI+ does not.

The InitRot function takes the angles of rotation for the three axis in degrees as input from the user controls and outputs values used in the sphere rotation calculations which are combined with calculations to construct the sphere itself. The sphere object calculations result in x,y,z coordinates to describe a 3-D sphere pixel by pixel, starting from an x coordinate at one polar end of the sphere object, calculating all associated circular y coordinates then incrementing x and repeat finding the associated y points etc, etc till the opposite pole is reached.

Comment out the line of code reading :

 if((j+i)%64 >= 0 && (j+i)%64 <=32) 

and you will see this incremental plotting of points results in a plain sphere as output. What this line does is selectively filter x points to, in effect, increment x sooner than usual so that a spiral from pole to pole is formed. The mod division is for creating multiple spirals instead of just one. You can see this by substituting the commented out line :

 if(Math.Abs(j-i) <=12)

for the line using mod division. You will have to input an x or y rotation first, because the initial pole view of the single spiral does not clearly show this. Incidentally, I tried using a Point array and then index it with unsafe pointers to form the spirals, but the results were too cumbersome. One line of code worked faster and better here for me. An array with varying indexed access to the Point data would open up more graphics design possibilities. So I am still working on it, but if a more experienced C# programmer could suggest a way to use the System.Array Class I am willing to listen.

The next if block of code :

if( z2 > 0 ) { ... 

checks the z coordinates to see if they output negative results. If they do, this means that the points in 3-D space are on the hidden side of the sphere. Usually these points are skipped and not drawn since the front surface is all we see. In this case, however, since the spirals have cutout portions that allow some of the back surface spirals to show through, the SetPixel Color parameter is set to a gray gradient for these. The front spirals are colored gradients. GDI+ has good color gradient methods available, but here again, it was easier to write it this way especially since I was dealing with 3-D and rotation changes to the graphics. A lot of code would be needed to define the boundaries or paths that GDI+ calls for.

Conclusion

Recent news from Microsoft is that Avalon, the graphics package with Longhorn will provide 3-D drawing support. Have fun experimenting with the program and be sure to send me any interesting or wild and zany designs you come up with!

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Explain More. norm.net 3:21 25 Jun '04   First glimsp of the article suggests it could be a better read if you explain step by step on how you achieved the effect. I'll hang fire with my vote 'till then. Sign In·View Thread·PermaLink 2.33/5 (2 votes) Re: Explain More. drositas 19:16 25 Jun '04   Which effect are you refering to? Color, spiraling, sphere construct? Sign In·View Thread·PermaLink 2.00/5 (1 vote) Slowness... Joel Holdsworth 1:54 25 Jun '04   I find that it is possible to get a huge speed increase by using unsafe code like this: bitmap = new Bitmap(bitmapsize.Width, bitmapsize.Height, PixelFormat.Format32bppArgb); //----- Get a lock on the data -----// BitmapData bitmapdata = bitmap.LockBits(new Rectangle(new Point(0, 0), gradientbitmapsize), ImageLockMode.WriteOnly, PixelFormat.Format32bppArgb); int stride = bitmapdata.Stride; //----- Work on the raw data -----// unsafe { byte *buffer = (byte *)(void *)(bitmapdata.Scan0); if(buffer == (byte*)0) throw new Exception("null bitmap buffer"); byte *p = buffer + (x + stride*y) * 4; *p = blue; p++; *p = green; p++; *p = red; p++; *p = alpha; } //----- Unlock -----// gradientbitmap.UnlockBits(bitmapdata); By doing this you may even be able to have the ball spinning in real time! Joel Holdsworth Sign In·View Thread·PermaLink 2.00/5 (2 votes)

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