11/11/2022 0 Comments Is opengl 4.4 or 4.5 better![]() ![]() Next, we come to bindless textures, an exciting new feature available only through the GL_ARB_bindless_texture extension. The seventh edition's cullindirect example demonstrates this feature. This change allows for using a shader or other GPU functionality to generate both a list of draws and the count, without CPU intervention. GL_ARB_indirect_parameters added a feature to allow the draw count to be placed in a buffer as well. This meant that if the draws were generated on the GPU, a roundtrip back to the CPU would be necessary–retrieving the value only to send it straight back to the GPU. (The sixth edition showed an example of this feature rendering an asteroid field.) In the original version of the function call, introduced in OpenGL 4.2, the number of draws in the buffer was passed as a parameter. Multi-Draw Indirect (MDI) FunctionsĪnother feature expanded in recent versions of OpenGL is the set of MDI functions, which allow a large list of parameters for draws to be placed in a buffer object and then sent to the GPU at once. Demonstrations of using persistent mapped buffers for shader parameters, vertex data, and texture data are included with the book's sample code in the pmbstreaming, ompparticles, and pmbfractal examples, respectively. This change allows an application to share a piece of memory between the CPU and GPU, and even deal with synchronization itself, which has implications for multithreading, fine-grained work generation, and efficient read-backs from the GPU to the CPU. OpenGL 4.4 made this use legal and well defined, so long as the application specifies its intention to use the buffer this way when it's allocated. Sometimes this kind of rendering would work, sometimes it would generate an error, and sometimes it wouldn't work but also wouldn't generate an error. However, because the overhead is so great for a driver to attempt to figure out whether any mapped buffer might be used by a particular draw, it wasn't guaranteed that you'd actually see that error, and most drivers didn't do the check at all. In prior versions of OpenGL, it was an error to attempt to render from a buffer while that buffer was mapped. Possibly the most interesting of the new features introduced since OpenGL 4.3 is persistent mapped buffers, which were included with the GL_ARB_buffer_storage extension and are now part of OpenGL 4.4 and 4.5. However, these features represent the cutting edge of graphics technology at this point in 2015, OpenGL is the only way to get them. Because these extensions have become more ubiquitous, I decided to showcase them. This marks a departure from the previous edition, in which I stayed away from extensions in order to ensure the widest possible user base for the code. The book contains examples of the use of all of these features, some of which are available only on very recent hardware with up-to-date drivers that expose specific extensions.
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