acrilige - Developer IT

backface culling error (in world space)

- by acrilige

I write simple software renderer. In my pipeline i have stage of backface culling. But looks like it has some error (see picture). I perform culling right after world transformation (is it correct?). (i can't insert picture in post coz i don't have enough points, so i just upload it (cube model): http://imageshack.us/photo/my-images/705/bcerror.png/) Vector3F view_dir(0.0f, 0.0f, 1.0f); std::vector<Triangle> to_remove; for (Triangle &t : m_triangles) { Vector4F e1 = t.v2 - t.v1; Vector4F e2 = t.v3 - t.v1; Vector3F normal( e1.y * e2.z - e1.z * e2.y, e1.z * e2.x - e1.x * e2.z, e1.x * e2.y - e1.y * e2.x ); normal.Normalize(); float dot = Dot(view_dir, normal); if (dot <= 0) to_remove.push_back(t); } for (Triangle& t : to_remove) m_triangles.erase(std::remove(m_triangles.begin(), m_triangles.end(), t), m_triangles.end()); Camera sits in origin and points in screen (RH). What is the reason? For better explanation i upload picture with cube rotation screenshots: http://imageshack.us/photo/my-images/842/bcmove.png/ UPDATED: The error occurs only when triangle has non-zero offset from origin UPDATED 2: If i process backface culling in clip space (after transforming all vertices with view and projection matrix), and just check z coordinate of triangle normal - it works perfect... Can i perform culing RIGHT BEFORE view/proj transforms? In this case looks like culling will not depends of projection and it's not right?.. UPDATED 3: I found answer and will post it in two hours - again coz of reputation lack.

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relationship between the model and the renderer

- by acrilige

I tried to build a simple graphics engine, and faced with this problems: i have a list of models that i need to draw, and object (renderer) that implements IRenderer interface with method DrawObject(Object* obj). Implementation of renderer depends on using graphics library (opengl/directx). 1st question: model should not know nothing about renderer implementation, but in this case where can i hold (cache) information that depends on renderer implementation? For example, if model have this definition: class Model { public: Model(); Vertex* GetVertices() const; private: Vertex* m_vertices; }; what is the best way to cache, for example, vertex buffer of this model for dx11? Hold it in renderer object? 2nd question: what is the best way for model to say renderer HOW it must be rendered (for example with texture, bump mapping, or may be just in one color). I thought it can be done with flags, like this: model-SetRenderOptions(RENDER_TEXTURE | RENDER_BUMPMAPPING | RENDER_LIGHTING); and in Renderer::DrawModel method check for each flag. But looks like it will become uncomfortable with the options count growth...

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backface culling error

- by acrilige

I write simple software renderer. In my pipeline i have stage of backface culling. But looks like it has some error (see picture). I perform culling right after world transformation. (i can't insert picture in post coz i don't have enough points, so i just upload it (cube model): http://imageshack.us/photo/my-images/705/bcerror.png/) Vector3F view_dir(0.0f, 0.0f, 1.0f); std::vector<Triangle> to_remove; for (Triangle &t : m_triangles) { Vector4F e1 = t.v2 - t.v1; Vector4F e2 = t.v3 - t.v1; Vector3F normal( e1.y * e2.z - e1.z * e2.y, e1.z * e2.x - e1.x * e2.z, e1.x * e2.y - e1.y * e2.x ); normal.Normalize(); float dot = Dot(view_dir, normal); if (dot <= 0) to_remove.push_back(t); } for (Triangle& t : to_remove) m_triangles.erase(std::remove(m_triangles.begin(), m_triangles.end(), t), m_triangles.end()); Camera sits in origin and points in screen (RH). What is the reason?

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