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copied!<p>One clarification to your way of thinking before we begin. In XNA - you draw a wireframe (outline) triangle, or a filled triangle or a textured triangle. There isn't anything lile "draw now" and "fill later". You can only draw something else on top of what's already in the framebuffer.</p> <p>Also <a href="http://en.wikipedia.org/wiki/Triangle_mesh#Index_array" rel="nofollow">here</a> is some background on what an indexed mesh is. This is the data fed into DrawUserIndexedPrimitives (vertices and triangles composed of indices into the sett of vertices).</p> <p>Given that, here's how the draw call works</p> <pre><code> _effect.Texture = texture; // This sets the texture up so the // shaders associated with this effect can access it // The color in each vertex is modulated with the texture color // and linearly interpolated across vertices _effect.VertexColorEnabled = true; foreach (var pass in _effect.CurrentTechnique.Passes) { pass.Apply(); // This sets up the shaders and their state // TriangleList means that the indices are understood to be // multiples of 3, where the 3 vertices pointed to are comprise // one triangle _device.DrawUserIndexedPrimitives(PrimitiveType.TriangleList, // The vertices. Note that there can be any number of vertices in here. // What's important is the indices array (and the vertexOffset, primitivecount, vertexCount) that determine // how many of the provided vertices will actually matter for this draw call _vertices, // The offset to the first vertex that the index 0 in the index array will refer to // This is used to render a "part" of a bigger set of vertices, perhaps shared across // different objects 0, // The number of vertices to pick starting from vertexOffset. If the index array // tried to index a vertex out of this range then the draw call will fail. _vertices.Count, // The indices (count = multiple of 3) that comprise separate triangle (because we said TriangleList - // the rules are different depending on the primitive type) _indices, // Again, an offset inside the indices array so a part of a larger index array can be used 0, // Number of indices. This HAS to be a multiple of 3 because we said we're rendering // a list of triangles (TrangleList). kvp.Value.Indices.Count / 3); } </code></pre> <p>I hope that is clear. Do let me know if you have any specific questions about each of the parameters and/or concepts and I can edit this post to clarify those points.</p> <p>Hope this helps!</p>

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