![]() ![]() When using instanced rendering, in the vertex shader we can use an input variable that holds the index of the instance that is currently being drawn. ![]() How can we do this when rendering all of them at once? Before a render call is made we need to setup the specific data for each item. Now, before we draw each instance we pass the different transformations and instance related data using uniforms. glDrawElements(GL_TRIANGLES, numVertices, GL_UNSIGNED_INT, 0)Īnd this is how the instanced version can be used: glDrawElementsInstanced(GL_TRIANGLES, numVertices, GL_UNSIGNED_INT, 0, numInstances) īut you may be wondering now how can you set the different transformations for each of those instances. This is a sample of how the glDrawElements is used. This function receives the same arguments as the glDrawElements plus one additional parameter which sets the number of instances to be drawn. In our case, since we are drawing elements we will use the function named glDrawElementsInstanced. In order to acomplish that OpenGL provides a set of functions named glDrawXXXInstanced to render a set of elements at once. ![]() This technique is called instanced rendering. When dealing with lots of similar objects it would be more efficient to render all of them using a single call. Each call to the glDrawElements function imposes an overhead that is repeated again and again for each GameItem instance. As it has been said in previous chapters, calls to OpenGL library should be minimized. We are basically iterating through all the game items inside a loop and performing a call to the function glDrawElements. ![]() The cause behind this is the way we are rendering them. In this case, although they may be simple objects with just a few triangles, performance can suffer. When drawing a 3D scene is frequent to have many models represented by the same mesh but with different transformations. ![]()
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