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Posted 27 November 2012 - 04:01 AM
Posted 27 November 2012 - 04:32 AM
I think that the lacking HDD support (think of Xbox I) on consoles was one of the major reasons to use streaming. The benefit of streaming is not only the reduced memory impact, but although the asynchroniously nature. Time isn't the most critical issue once you start streaming.
I can't imagine they stream them from the DVD
Why not, when using DDS you can access the single mipmap levels easy enough. And you don't need to read every single mipmap-level, dividing your texture mipmaps into two sections (low/hi) is often enough.
(i.e. one texture file with all the MIP levels in it)
Loading and decompression can be done in an async. thread. Uploading the data to the videocard is most likely done by DMA, therefore the time impact could be quite small.
So if they are separate, isn't it going to be pretty slow to load in an image, lock the texture on the card,
Edited by Ashaman73, 27 November 2012 - 04:37 AM.
Posted 27 November 2012 - 05:00 AM
I've seen some systems that stream from DVD to RAM and the HDD at the same time, so that next time it can just stream from the HDD (if one is present). This means that people with cheap (no HDD) Xboxes either have longer loading screens, or lower quality graphics for longer during streaming events.
I was wondering if they will be streaming their textures from the DVD (slow??) or whether they might dump a load of textures (for the current level perhaps) to HDD temporarily (faster) and stream them from there.
The problem is that when reading from DVD, you want to read data in at least 32KiB blocks, and you want to read as many contiguous blocks as possible. The most optimal layout would have all the bottom-few mips of all the textures in your "level" packed tightly together, then all the next mips next to each other, then all the next-largest mips, etc... (assuming that you're streaming in a "level's worth" of textures at a time).
when using DDS you can access the single mipmap levels easy enough
The details for how you'd do this depend on the graphics API. On the consoles, you can manage video memory yourself, so if you know you're not going to create artefacts (because you know that you've set the min-mip-level render-state so that the incoming mips aren't going to be read by the GPU), then you can stream data into the texture's memory allocation without locking.
isn't it going to be pretty slow to load in an image, lock the texture on the card, update it with the incoming higher level MIPs and then unlock it again?
Edited by Hodgman, 27 November 2012 - 05:06 AM.
Posted 27 November 2012 - 06:36 AM
Posted 27 November 2012 - 07:49 AM
Definately. If you're making a PC game, you don't need to put in half the optimisation effort that console devs do! Firstly you'll be loading your data from a HDD (or even SSD) instead of a DVD, and secondly, you don't have some platform gatekeeper that will block the release of your game unless you meet arbitrary quality requirements on loading screens
I'm guessing it's better to just get streaming working in general and then concentrate on the efficiency of loading data.