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riz

OpenGL simple 2D graphics API in OpenGL or DirectX?

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Hi everyone, I''m taking a graphics class and I have to write a basic wireframe render which does backface culling. As part of the project, we are allowed to use OpenGL or DirectX, but only for dumping out our calculations to the screen. This means I can only use simple calls like "set pixel at x,y" or "draw line from pixel x,y to a,b". The rest of the rendering, such as going through the viewing pipeline, backface culling, etc. I have to do myself, I just need a simple API in a C++ window that can draw to the screen, so once I have done all the rendering, I can make the simple calls to the grpahics api to draw my stuff to the window. Do you have any suggestions as to what API i could use? The professor suggested that C++ and OpenGL was a good combination. Thanks, Riz

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I''ve done pretty much the same sorts of things in my graphics classes. I always used C++ and GLUT, and I never had any problems.

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Hi mmelson,

Thanks for replying. I''ve never used GLUT before, but I looked at the API, and it doesn''t seem to have any functions to draw basic primitives, such as lines and points. Could you tell me what kind of setup you had for your graphics programs? I''d really appreciate any help,

thanks,
riz

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im am currently doing something similar, and am using GLUT, i currently using

glColor3f for my colour
glVertex2i for my put pixel,

but if any 1 actually knows how i can get direct access to the video memory like in direct draw in opengl i would be very happy :D as im sure glVertex2i is pretty slow

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GLUT is a small convenience toolkit for OpenGL, it handles things like the windowing system, and rudimentary input. All drawing is done through OpenGL.

riz, I think OpenGL is pretty well suited for what you have in mind. You should also consider GLUT to get a fast working OpenGL framework running, if you don''t need any fancy features.

supagu: drawing individual pixels by glVertex is pretty much the slowest way there is OpenGL is primarily a vector API. Either you use the texture method (create a texture of the size of the screen, directly write your pixels to it, and finally render it to the screen with a single quad), or drop OpenGL and use something like DirectDraw or, better, SDL.

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Ok I must be getting this all wrong but:

My assignment is to make a basic renderer from scratch. Once all my points have been transformed to their pixel positions, I have use some API to "dump" out the graphics to the screen, using simple functions like "draw line" in OpenGL or some graphics package. Basically, I can''t use OpenGL''s 3D capability at all.

Since OpenGL is primarily an API for 3D Graphics, I''m having trouble figuring out what settings to put for setting the GL camera and perpective matrix to ensure that I get only 2D output.

if anyone has any other graphics package, or a code example in GDI (native windows graphics calls) I would really appreciate it.

thanks,
riz

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OpenGL doesn''t require you to use the 3D features in any way. Every 3D API can be used as a 2D API, if you ignore the 3rd dimension.

You simply setup a 2D orthographic camera, by using glOrtho():

glOrtho(0, 1024, 0, 768, -1, 1);

That would be for a 1024x768 screen, as an example. You can now address the screen coordinates in the (0..1023/0..767) range. To plot a point, or draw a line, you use the glVertex2() function family. This works very well, if you want to process 2D vector graphics.

If you want direct raw access to each pixel, however, then this method is not optimal. This is the case, if you want to write your own rasterizer, and line drawing functions.

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aahhh I see

Thanks Yann L, I was just confused about how to set up an orthogonal camera, but one simple function call is very nice, hehe.

Thanks for everyone''s help, I''m going to go and try it out!

riz

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