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Adam Jachocki

DirectxTK and basic concept of drawing models

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Hi, I am completely newbie. I've been reading about DirectX for 2, 3 months now and the only thing I am able to do is to draw a simple model on a scene (with lighting).

I started to do things using DirectXTK. But I think I don't understand some basic concepts, so maybe someone would be so kind and will explain them for me.

So I tried to create basic scene with anchor and some models. By anchor I mean just x, y, z axes.

So I did something like that (I am using basic examples from here: https://github.com/Microsoft/DirectXTK/wiki/Getting-Started

    Vector3 originVector(0.f, 0.f, 0.f);
    m_batch->DrawLine(VertexPositionColor(originVector, Colors::Red), VertexPositionColor(Vector3::UnitX, Colors::Red));
    m_batch->DrawLine(VertexPositionColor(originVector, Colors::Yellow), VertexPositionColor(Vector3::UnitY, Colors::Yellow));
    m_batch->DrawLine(VertexPositionColor(originVector, Colors::Green), VertexPositionColor(Vector3::UnitZ, Colors::Green));

Batch is just primitive batch(with VertexPositionColor) that I use to drawing axes.

This code gives me beautiful colorful axes.

But now I wanted to add a model. Simple sphere. So I did (before drawing axes):

m_shape->Draw(m_world, m_view, m_proj, Colors::Red);

(m_world is identity matrix)
And then first problem arouse. My axes now all have red color. Actually they get the color that my sphere has. Why is that?

Next, I wanted to move the sphere somewhere else, so I did:

Matrix m1 = Matrix::CreateTranslation(Vector3(-5.f, -2.f, -5.f));
m_shape->Draw(m1, m_view, m_proj, Colors::Red);

And what happened? My axes moved with the sphere. Now they are not drawn in place that I wanted, but they "come from inside" the sphere. Why is that?

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I haven't used DirectXTK, but maybe you're calling m_shape->Draw() inbetween m_batch->Begin() and m_batch->End(). I could be wrong, but I don't think its meant to be used like that. That's the only reason I can think of for the color changing.

As for the axes translation problem, I think you are changing the world matrix which I guess is effecting the other thing being drawn after it, I'm not sure how the Draw function works. In regular DirectX and OpenGL you would create a shader, and pass the same matrices as you do in m_shape->Draw(), and that would effect the entire draw call. Any changes to the matrices would effect the next draw calls, which I think might be happening with the axes. You might need to call something like SetWorld(identityMatrix) before rendering the axes, I don't know what exactly is suppose to do that, since I don't even know if m_batch has a function like that.

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On 12/1/2017 at 4:31 PM, Adam Jachocki said:

m_shape->Draw(m_world, m_view, m_proj, Colors::Red);

What is the type of shape? Is this part of DirectXTK or is this something you wrote yourself, since i do not see to find a member method with that signature.

If this method does not use the DirectXTK's PrimitiveBatch internally you may not call it between PrimitiveBatch::Begin() and PrimitiveBatch::End() like @Yxjmir pointed out. The PrimitiveBatch (and SpriteBatch) modify the pipeline. This is already the case when calling PrimitiveBatch::Begin(). So you probably override something you do not want in both cases.

Start your .exe with https://github.com/baldurk/renderdoc, take a screenshot and notice the sequence of pipeline calls. Here, you will probably notice some wrong states (buffers, shaders, whatever) of your m_shape->Draw interferring with your line drawing.

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