XNA - Drawing Quads (and primitives) in right order

问题

I'm fairly new to 3D-stuff in XNA and unfortunately I have encountered a problem I can't find the solution for. (Don't even know what the problem is).

To cut it short: I am drawing quads in my game using:

        effect.World = Matrix.Identity *
            Matrix.CreateRotationX(Rotation.X) *
            Matrix.CreateRotationY(Rotation.Y) *
            Matrix.CreateRotationZ(Rotation.Z) *
            Matrix.CreateTranslation(Position);

        // Apply camera-matrixes
        effect.View = viewMatrix;
        effect.Projection = projectionMatrix;

        graphics.VertexDeclaration = vertDec;

        // Begin effect drawing
        effect.Begin();
        foreach (EffectPass pass in
            effect.CurrentTechnique.Passes)
        {
            pass.Begin();
            graphics.DrawUserIndexedPrimitives
                <VertexPositionNormalTexture>(
                PrimitiveType.TriangleList,
                quad.Vertices, 0, 4,
                quad.Indexes, 0, 2);
            pass.End();
        }

        effect.End();

My effect also has these properties:

        this.effect.TextureEnabled = true;
        this.effect.Texture = texture;

And it works. My quad is drawn nicely and me is happy. However there is one slight problem. If one quad is behind another quad or regular model the way that determines which is drawn on top is the order that I draw them in.

Lets say I draw Quad A before Quad B, then B will be shown as on top of Quad A even if it is 40 units lesser in the Z-axis. Looks very confusing I must say! ;)

Now I haven't had any problem like this with my regular meshes, it is when primitives are involved things get this messy. The very same problem goes for drawing regular lines:

            graphics.DrawUserIndexedPrimitives<VertexPositionColor>(
                PrimitiveType.LineStrip,
                pointList,
                0,  // vertex buffer offset to add to each element of the index buffer
                6,  // number of vertices in pointList
                new short[] { 0, 1 },  // the index buffer
                0,  // first index element to read
                1   // number of primitives to draw

So what I'm asking really is:

A) Is this normal? Should I build a special engine which decides when to draw what? I can easily work around this in my project by drawing stuff at the right time but I can imagine a game where I could not. A fps for example couldn't draw its billboards all over the place! ;)

B) If this is not normal, what could be the cause and what would be a solution/good way to debug the error.

I would appreciate any help to sort this out! :)

回答1:

It sounds like you've got the depth buffer turned off. Perhaps you are drawing sprites before hand? (Using SpriteBatch will change various render states needed for normal 3D drawing.)

Try adding this line of code before you draw any 3D objects:

GraphicsDevice.RenderState.DepthBufferEnable = true;

回答2:

Thanks for answering this question! Just a follow up for anybody else who wants to know about this answer. In xna 4.0, it has changed a little bit.

Some 3D tile objects were transparent to other 3D objects. This was due to the removal of:

GraphicsDevice.RenderState.DepthBufferEnable = true;

In XNA 4 this was replaced by:

DepthStencilState depthBufferState = new DepthStencilState(); 
depthBufferState.DepthBufferEnable = true;
GraphicsDevice.DepthStencilState = depthBufferState;

Taken from this source: http://www.hexworld.co.uk/blog/?cat=9

来源：https://stackoverflow.com/questions/3093405/xna-drawing-quads-and-primitives-in-right-order

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xna

drawing

primitive