# EngineCoder

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1. ## New to OpenGL. Trying to figure it all out.

No, you must multiply the vertex position with that matrix: gl_Position = MVP * a_position;
2. ## What are the basics to making a Game Engine?

I have written game/rendering engines both for fun and professionally. I don't always have a use case for my engine, but when deciding on what features I'll develop, I focus on those that are needed in games like Half-Life or Deus Ex, because some day I want to be part of a team working on something like that. In the mean time, I sometimes do small indie games using my engine so I get to learn game development and not just engine development. Doing real games using your own engine is a good way to test its power. When developing an engine, I do it in the perspective of the engine's user, and try to make everything as seamless as possible for them. First I write API calls into a tech demo, then I implement them, so it's kind of a top-down process for me.

Xcode includes a handy tool called Instruments that can be used to find bottlenecks.
4. ## What's wrong with my tangent calculation?

Most tutorials do it that way, like: http://www.terathon.com/code/tangent.html
5. ## What's wrong with my tangent calculation?

Some of my triangles render as if they're pointing away from the light. I can fix them by rotating their UV map upside down. void Mesh::generateTangents() { for (size_t v = 0; v < m_vertices.size(); ++v) { m_vertices[ v ].tangent = Vec4( 0.0f, 0.0f, 0.0f, 0.0f ); } m_tangents.resize ( m_indices.size() ); m_bitangents.resize( m_indices.size() ); bool degenerateFound = false; for (size_t f = 0; f < m_indices.size(); ++f) { const Vec3& p1 = m_vertices[ m_indices[ f ].a ].position; const Vec3& p2 = m_vertices[ m_indices[ f ].b ].position; const Vec3& p3 = m_vertices[ m_indices[ f ].c ].position; const TexCoord& uv1 = m_vertices[ m_indices[ f ].a ].texCoord; const TexCoord& uv2 = m_vertices[ m_indices[ f ].b ].texCoord; const TexCoord& uv3 = m_vertices[ m_indices[ f ].c ].texCoord; const TexCoord deltaUV1 = uv2 - uv1; const TexCoord deltaUV2 = uv3 - uv1; const float area = (deltaUV1.u * deltaUV2.v - deltaUV1.v * deltaUV2.u); Vec3 tangent; Vec3 bitangent; if (std::fabs( area ) > 0.00001f) { const Vec3 deltaP1 = p2 - p1; const Vec3 deltaP2 = p3 - p1; tangent = (deltaP1 * deltaUV2.v - deltaP2 * deltaUV1.v) / area; bitangent = (deltaP1 * deltaUV2.u - deltaP2 * deltaUV1.u) / area; } else { degenerateFound = true; } Vec4 tangent4( tangent.x, tangent.y, tangent.z, 0.0f ); m_tangents[ f ] = tangent4; m_bitangents[ f ] = bitangent; } if (degenerateFound) { std::cout << std::endl << "Warning: Degenerate UV map in " << name << ". Author needs to separate texture points in mesh's UV map." << std::endl; } m_vbitangents.resize( m_vertices.size() ); // For every vertex, check how many faces touches // it and calculate the average of their tangents. for (size_t vertInd = 0; vertInd < m_vertices.size(); ++vertInd) { Vec4 tangent( 0.0f, 0.0f, 0.0f, 0.0f ); Vec3 bitangent; for (size_t faceInd = 0; faceInd < m_indices.size(); ++faceInd) { if (m_indices[ faceInd ].a == vertInd || m_indices[ faceInd ].b == vertInd || m_indices[ faceInd ].c == vertInd) { tangent += m_tangents [ faceInd ]; bitangent += m_bitangents[ faceInd ]; } } m_vertices[ vertInd ].tangent = tangent; m_vbitangents[ vertInd ] = bitangent; } for (size_t v = 0; v < m_vertices.size(); ++v) { Vec4& tangent = m_vertices[ v ].tangent; const Vec3& normal = m_vertices[ v ].normal; const Vec4 normal4( normal.x, normal.y, normal.z, 0.0 ); // Gram-Schmidt orthonormalization. tangent -= normal4 * normal4.dot( tangent ); tangent.normalize(); // Handedness. TBN must form a right-handed coordinate system, // i.e. cross(n,t) must have the same orientation than b. const Vec3 cp = normal.cross( Vec3( tangent.x, tangent.y, tangent.z ) ); tangent.w = cp.dot( m_vbitangents[v] ) > 0.0f ? 1.0f : -1.0f; } } I'm calculating my bitangents in the vertex shader and multiplying them with the handedness sign. I'm transforming my camera and point light position from world space to object space by multiplying them with inverse model matrix before transforming them to tangent space. If I visualize my TBN vectors, normals are pointing away from the surface and tangents and bitangents are orthogonal. void main() { gl_Position = u_modelViewProjectionMatrix * vec4( a_position, 1.0 ); v_texCoord = a_texCoord; vec3 bitangent = normalize( cross( a_normal, a_tangent.xyz ) ) * a_tangent.w; // .w is the handedness. mat3 toTangentSpace = mat3( a_tangent.x, bitangent.x, a_normal.x, a_tangent.y, bitangent.y, a_normal.y, a_tangent.z, bitangent.z, a_normal.z ); vec3 mDirToLight = normalize( u_lightPosition.xyz - a_position ); // Light position is in object-space. vec3 mDirToCamera = normalize( u_cameraPosition.xyz - a_position ); // Camera position is in object-space. v_dirToLight = toTangentSpace * mDirToLight; v_viewDir = toTangentSpace * mDirToCamera; }
6. ## Camera Intilization in OpenGL ES 2.0

Here's my lookat() implementation: void Matrix::makeLookAt( const Vec3& aEye, const Vec3& aCenter, const Vec3& aUp, float* aMatrix ) { assert( aMatrix ); Vec3 forward = aCenter - aEye; forward.normalize(); Vec3 right = forward.cross( aUp ); right.normalize(); const Vec3 up = right.cross( forward ); aMatrix[ 0 ] = right.x; aMatrix[ 4 ] = right.y; aMatrix[ 8 ] = right.z; aMatrix[ 12 ] = 0; aMatrix[ 1 ] = up.x; aMatrix[ 5 ] = up.y; aMatrix[ 9 ] = up.z; aMatrix[13 ] = 0; aMatrix[ 2 ] = -forward.x; aMatrix[ 6 ] = -forward.y; aMatrix[10 ] = -forward.z; aMatrix[14 ] = 0; aMatrix[ 3 ] = aMatrix[ 7 ] = aMatrix[ 11 ] = 0.0f; aMatrix[15 ] = 1.0f; float translate[ 16 ]; Matrix::identity( translate ); translate[ 12 ] = -aEye.x; translate[ 13 ] = -aEye.y; translate[ 14 ] = -aEye.z; multiply( translate, aMatrix, aMatrix ); }
7. ## learning and create engine

For good up-to-date OpenGL practices try this reference: http://www.arcsynthesis.org/gltut/
8. ## Cyberjack (iOS Universal) action/puzzler

http://itunes.apple....73873?ls=1&mt=8 In Cyberjack you can shoot bots, disarm explosives, hack computers and upgrade your character with augs like stealth and shield. I made the game alone in 10 months using mostly open source tools. Any questions or feedback is appreciated!
9. ## Difference between Game Engine and APIs

XNA is not a game engine, it's a framework. DLL files can contain many things, including drivers.
10. ## Rendering wavefront obj files with VBOs

Production code usually uses custom file formats that are in binary and have their layout resembling the actual layout on GPU, because it's faster/easier to load. Ideally you should write exporters to popular modeling tools such as 3ds Max and Blender.
11. ## GLSL Compilation error

How do you create your OpenGL context? You have to specify the version when creating it.
12. ## Efficiently Extruding Shadow Volumes

In C++, there is std::map. Also, you most likely will want to do the extrusion in a vertex shader.
13. ## C++ in the iOS

You can also configure Xcode to compile everything as Objective-C++ so you don't have to rename any files. I did this in my cross-platform engine.
14. ## [Problem] Pointlight Shader Wont Work

Integers are not automatically casted to float in shaders. You must use 1.0 instead of 1 etc.
15. ## Quick tutorials to migrate from DirectX to OpenGL

Quote:Original post by Chetanhl EDIT : regarding SDL i have been asked to use OpenGL only so GLUT & GLEW will be better i think, also i may have to work on 3D apps and SDL is 2D. SDL contains the same functionality as GLUT, and much more. It's used to set up the window, get input etc. Also, it's somewhat wrong to say that it's 2D because you can create and use an OpenGL context with it.