# Vertices problem - real new to this but still strange

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Liron    122
Hello all, I'm just beginning with DirectX and I have a very strange problem which I can't explain, so I thought you could probably help. I took the Vertices example from the SDK tutorials (October Update but i'm sure it's all the same), added a new set of vertices (3, for a triangle) to the vertices variable, changed the size of the created vertex to hold the new vertices as well and changed the DrawPrimitive's "PrimitiveCount" parameter to 2 (so i'd expect to see 2 triangles as supplied by my 6 vertices array with a triangle list primitive type). I also changed the window size to 640*480 instead of the very small 100*100 it was in the original sample. When I ran the sample I expected to see two triangles but instead I saw only the first one (the original one). After playing for awhile I figured out something strange - my new vertices are defined like this: { 400.0f,200.0f,0.5f,1.0f,0xffff0000,}, { 500.0f,250.0f,0.5f,1.0f,0xffff0000,}, { 600.0f,200.0f,0.5f,1.0f,0xffff0000,}, If I was to change the Y coordinate to 250.0f, 200.0f, 250.0f respectivly I would see the second triangle as expected. What's wrong here? My logic and instincts tells me there must be an error somewhere else but I have no idea where to look. It's not a problem with a video card or drivers as I tested this on another machine with the same results. Please help a newbie Thanks Liron

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steg    390
I guess it could be you are drawing the triangle counterclockwise with your first set of vertices and thus they are culled by d3d. When you change the y coordinate to the values of 250.0f,200.0f and 250.0f you are then drawing the triangle clockwise which is correct.

Hope this helps,
Steve

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Liron    122
Great! Thank you very much, that works now. Nowhere in my sources of reading does it say anything about rendering clockwise... Only after searching really deep I found a mentioning and also in the DirectX SDK docs and not anywhere in the books I'm reading, and they're considered good books (for beginners)

Anyway - thank you very much, now I can continue with more understanding

Bye
Liron

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