5 replies to this topic

[amtri]

Hello,

I'm having some basic problems with Direct3D9 and I'm hoping somebody can point me in the right direction. I have succeeded in using Direct3D in the past, but I had separate vertex buffers for each primitive. I would then fill the vertex buffer, then call a DrawPrimitive a single time. It all worked fine.

Now I have the following sequence:

1) Create a vertex buffer
2) Add one triangle to the buffer. At this point, I call

Lock(0,0,&bfr,D3DLOCK_DISCARD)
copy triangle vertex data into bfr, starting at bfr[0]

3) Add second triangle to the buffer. Here I assume I do not need to call Lock again as I have bfr saved. I simply copy the triangle vertex into bfr, starting at bfr[3] ("3" means I have the stride into consideration).

4) Now I'm going to draw. I do

BeginScene
SetFVF
SetStreamSource(0,VB,0,size);
DrawPrimitive(D3DPT_TRIANGLELIST,0,1);

5) Now the second triangle. Since BeginScene and SetFVF have already been called I now call

SetStreamSource(0,VB,0,size); (again)
DrawPrimitive(D3DPT_TRIANGLELIST,3,1);

6) Finally, I do

EndScene
Present

The image I get is completely wrong. So my questions:

(a) Is there a way to debug Direct3D9 so I can actually see what it's trying to do and why it displayed the image it did?
(b) Am I doing something obviously wrong above?
© I will keep the vertex buffer for a while as I rotate the model. This means that the drawing part gets repeated many times, while copying the data to the buffer is done once only. Once I'm done with viewing this I will Release the vertex buffer altogether. In other words, I will write to the "bfr" pointer many times, while Lock has been called only once. Am I using the right options in the functions above?
(d) I tried using the DirectX Control Panel where I choose to use the Debug version of Direct3D. Should I expect to see any output anywhere in Visual Studio - or anywhere else, for that matter?

Thanks.

[mhagain]

I don't see where you're saying that you're calling Unlock.

Aside from that, SetStreamSource is only necessary once here, and if you don't change any states you can draw both triangles in a single call.

[amtri]

mhagain,

You're right: I forgot to mention that I'm calling Unlock right before the call to BeginScene. Sorry about that...

I know I can draw both triangles in a single call - in theory. In practice, I don't really know how the application is going to send graphics calls to me. In reality, I'm drawing around 0.5 million triangles - not one at a time, but in groups. Or triangle strips, or lines, or points, etc. I used 2 triangles in the example for simplicity, but it could really be anything.

Any thoughts on how I can debug this?

Thanks.

[mhagain]

Before BeginScene? That's wrong then. The usage goes like this:

Lock
Copy data in
Unlock
SetStreamSource
DrawPrimitive

[amtri]

mhagain,

Thanks. I've corrected that. But my problem didn't go away. I finally figured it out... in the new code I mistakenly used D3DFVF_XYZRHW rather than D3DFVF_XYZ. That's what happens when you use "cut and paste" to generate new code :-(!!!

I still wish there were a way to debug Direct3D9 so I would see this was happening.

Thanks again!

[mhagain]

Fire up the DirectX control panel (it's available in your Start menu) and switch it to Debug mode. Also, using PIX (Start menu too) and checking the HRESULT from every operation are both highly recommended.