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POimproving the speed of the execution of that piece of code
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2013-11-29T04:01:55.653
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2013-11-29T04:08:06.933
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I have two methods used to render a grid. First one : <pre><code>void Grid::openglRender(){ glPolygonMode( GL_FRONT_AND_BACK, GL_LINE ); glBegin(GL_TRIANGLES); glColor3f(1.0f, 1.0f, 0.0f); Node* A, * B, * C, * D; for(size_t X=0 ; X<sizeX-1 ; X++)for(size_t Z=0 ; Z<sizeZ-1; Z++){ A = &nodes[X*sizeZ+Z]; B = &nodes[(X+1)*sizeZ+Z]; C = &nodes[X*sizeZ+(Z+1)]; D = &nodes[(X+1)*sizeZ+(Z+1)]; glVertex3f(A->x, A->y, A->z); glVertex3f(B->x, B->y, B->z); glVertex3f(C->x, C->y, C->z); glVertex3f(B->x, B->y, B->z); glVertex3f(D->x, D->y, D->z); glVertex3f(C->x, C->y, C->z); } glEnd(); }; </code></pre> Second one : <pre><code>void Grid::openglRender(){ glPolygonMode( GL_FRONT_AND_BACK, GL_LINE ); glBegin(GL_TRIANGLES); glColor3f(1.0f, 1.0f, 0.0f); for(size_t X=0 ; X<sizeX-1 ; X++)for(size_t Z=0 ; Z<sizeZ-1; Z++){ glVertex3f(nodes[X*sizeZ+Z].x, nodes[X*sizeZ+Z].y, nodes[X*sizeZ+Z].z); glVertex3f(nodes[(X+1)*sizeZ+Z].x, nodes[(X+1)*sizeZ+Z].y, nodes[(X+1)*sizeZ+Z].z); glVertex3f(nodes[X*sizeZ+(Z+1)].x, nodes[X*sizeZ+(Z+1)].y, nodes[X*sizeZ+(Z+1)].z); glVertex3f(nodes[(X+1)*sizeZ+Z].x, nodes[(X+1)*sizeZ+Z].y, nodes[(X+1)*sizeZ+Z].z); glVertex3f(nodes[(X+1)*sizeZ+(Z+1)].x, nodes[(X+1)*sizeZ+(Z+1)].y, nodes[(X+1)*sizeZ+(Z+1)].z); glVertex3f(nodes[X*sizeZ+(Z+1)].x, nodes[X*sizeZ+(Z+1)].y, nodes[X*sizeZ+(Z+1)].z); } glEnd(); }; </code></pre> for me the first one looks better in term of number of operations, in <code>glVertex3f</code> I just use the pointer to get a value. In the second method each time I have to multiply and to add something. But at the running time I don't realy feel a difference. So I'm right when I say that the first one is better ? or maybe whatever I chose the compiler know better than I, what to do to get the best... maybe it would be a bit better if I declare <code>X</code> and <code>Z</code> before the <code>for</code> loops to avoid especially the declaration and destruction <code>sizeX</code> times of Z Also I guess, the best would be to create a list (one time, stored ro be reused every frame) with all nodes in the order to be traversed to create the grid instead of using two <code>for</code>
Tags
<c++><linux><opengl><optimization>
Title
improving the speed of the execution of that piece of code
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1. PO
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1. USThe Unholy Metal Machine
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1. USThe Unholy Metal Machine
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1. COChances are good that the call overhead of `glVertex3f (...)` ***far*** exceeds any fancy pants pointer arithmetic hacks you can throw at this problem. There is literally no point in micro-optimizing immediate mode like this, you should switch to indexed vertex arrays and call it time better spent. But if you insist, you can make this nightmare last longer if you throw `glVertex3fv (... )` into the mix for yet another micro-optimization.
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 POimproving the speed of the execution of that piece of code
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 USAndon M. Coleman
2. CO@AndonM.Coleman sounds good, to be honnest I never used vertex array, so I even didn't thought of it when I wrote that code. I read few about them in some book. I will read more about that at the library tomorow
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 POimproving the speed of the execution of that piece of code
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 USThe Unholy Metal Machine

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